Bendix Commercial Vehicle Systems TROUBLE SHOOTING COMPRESSOR User Manual

This troubleshooting guide obsoletes and supersedes all previous published

troubleshooting information relative to Bendix® air compressors.

Advanced Troubleshooting Guide

for Air Brake Compressors

The guide consists of an introduction to air brake charging system components, a table showing recommended vehicle maintenance schedules, and a troubleshooting symptom and remedy section with tests to diagnose most charging system problems.

Symptom Page Number

Air

Air brake charging system:

Slow build (9.0) ...................9 - 10

Doesn’t build air (10.0) .................11

Air Dryer:

Doesn’t purge (14.0) ..................12

Safety valve releases air (12.0) ..........12

Compressor:

Constantly cycles (15.0) ...............13

Leaks air (16.0) ......................13

Safety valve releases air (11.0) ..........11

Noisy (18.0) ........................13

Reservoir:

Safety valve releases air (13.0) ..........12

INDEX

Symptom Page Number

Coolant

Compressor leaks coolant (17.0). . . . . . . . . . . . 13

Engine

Oil consumption (6.0) .....................9

Oil

Oil Test Card results (1.0) ..................4

Oil is present:

On the outside of the compressor (2.0) .....5

At the air dryer purge/exhaust

or surrounding area (3.0) ..............5

In the supply reservoir (4.0) ........... 6 - 8

At the valves (5.0) .....................8

At air dryer cartridge (7.0) ...............9

In the ping tank or compressor

discharge aftercooler (8.0) .............9

Test Procedures

(1) Oil Leakage at Head Gasket ............14

(2) System Leakage .....................14

(3) Compressor Discharge and

Air Dryer Inlet Temperature ............14

(4) Governor Malfunction .................14

(5) Governor Control Line .................15

(6) Compressor Unloader .................15

BASIC Test Information ................ 17-19

Maintenance & Usage Guidelines

Maintenance Schedule and Usage Guidelines

(Table A) .................... 3

Note: The technical bulletins referenced in this

document are available at www.Bendix.com.

*This guide is only for vehicles that use desiccant air dryers.

Introduction to the Air Brake Charging System

Powered by the vehicle engine, the air compressor builds the air pressure for the air brake system. The air compressor is typically cooled by the engine coolant system and lubricated by the engine oil supply.

The compressor's unloader mechanism and governor (along with a synchro valve for the Bendix® DuraFlo 596

™

air compressor) control the brake system air pressure between a preset maximum and minimum pressure level by monitoring the pressure in the service (or “supply”) reservoir. When the air pressure becomes greater than that of the preset “cut-out”, the governor controls the unloader mechanism of the compressor to stop the compressor from building air and also causes the air dryer to purge. As the service reservoir air pressure drops to the “cut-in” setting of the governor, the governor returns the compressor back to building air and the air dryer to air drying mode.

As the atmospheric air is compressed, all the water vapor originally in the air is carried along into the air system, as well as a small amount of the lubricating oil as vapor.

The duty cycle is the ratio of time the compressor spends building air to the total engine running time. Air compressors are designed to build air (run “loaded”) up to 25% of the time. Higher duty cycles cause conditions that affect air brake charging system performance which may require additional maintenance. Factors that add to the duty cycle are: air suspension, additional air accessories, use of an undersized compressor, frequent

stops, excessive leakage from ttings, connections,

lines, chambers or valves, etc. The discharge line allows the air, water-vapor and

oil-vapor mixture to cool between the compressor and air dryer. The typical size of a vehicle's discharge line, (see column 2 of Table A on page 3) assumes

a compressor with a normal (≤ 25%) duty cycle and

operating in a temperate climate. See Bendix and/ or other air dryer manufacturer guidelines as needed.

When the temperature of the compressed air that enters the air dryer is within the normal range, the air dryer can remove most of the charging system oil. If the temperature of the compressed air is above the normal range, oil — as oil-vapor — is able to pass through the air dryer and into the air system. Larger diameter discharge lines and/or longer discharge line lengths can help reduce the temperature.

The discharge line must maintain a constant slope

down from the compressor to the air dryer inlet tting to avoid low points where ice may form and block the ow.

If, instead, ice blockages occur at the air dryer inlet,

insulation may be added here, or if the inlet tting is a typical 90 degree tting, it may be changed to a straight or 45 degree tting. For more information on how to

help prevent discharge line freeze-ups, see Bendix Bulletins TCH-008-021 and TCH-008-022 (available on www.bendix.com). Shorter discharge line lengths or insulation may be required in cold climates.

The air dryer contains a lter that collects oil droplets, and a desiccant bed that removes almost all of the remaining water vapor. The compressed air is then passed to — and stored in — the air brake service (supply) reservoir. The oil droplets and the water collected are automatically purged when the governor reaches its “cut-out” setting.

For vehicles with accessories that are sensitive to small amounts of oil, we recommended installation of a Bendix® PuraGuard® oil coalescing lter, designed to further minimize the amount of oil present.

Discharge Line

Compressor

Optional “Ping” Tank

Air Dryer

Governor

(Governor plus Synchro valve for the

Bendix® DuraFlo 596™ Compressor)

The Air Brake Charging System supplies the

compressed air for the braking system as well as other air accessories for the vehicle. The system usually consists of an air compressor, governor, discharge line, air dryer, and service reservoir.

Service Reservoir

(Supply Reservoir)

Reservoir Drain

Table A: Maintenance Schedule and Usage Guidelines

Regularly scheduled maintenance is the single most important factor in maintaining the air brake charging system.

Column 1

Recom- Recom- Acceptable Typical Discharge mended mended Reservoir Compressors Line Air Dryer Reservoir Oil Contents No. of Spec'd Cartridge Drain at Regular

Vehicle Used for:

Axles Replacement1 Schedule2 Drain Interval

Low Air Use

Compressor with less than 15% duty cycle

e.g. Line haul single trailer

w/o air suspension, air over

hydraulic brakes.

Compressor with up to 25% duty cycle

e.g. Line haul single trailer

with air suspension,

school bus.

High Air Use

Compressor with up to 25% duty cycle

less

550 air compressor

Tu-Flo

air compressor

Bendix

BA-921

e.g. Double/triple trailer, open

highway coach/RV, (most)

pick-up & delivery, yard or

terminal jockey, off-highway,

construction, loggers, concrete

mixer, dump truck, re truck.

Compressor with up to 25% duty cycle

less

Bendix

750 air compressor

Tu-Flo

air compressor

™

Bendix

e.g. City transit bus, refuse,

bulk unloaders, low boys,

urban region coach, central

tire ination.

less

, or DuraFlo 596

BA-922

Column 2 Column 3 Column 4 Column 5

I.D.

1/2 in.

For oil carry-over

control4 suggested

5/8 in. 9 ft.

For oil carry-over

control4 suggested

Length

6 ft.

upgrades:

9 ft.1/2 in.

upgrades:

Every 3

Years

Recommended

Every

Month -

Max of every

90 days

5/8 in. 12 ft.

1/2 in.

12 ft.

Every 2

For oil carry-over

control4 suggested

upgrades:

Years

5/8 in. 15 ft.

Every

Month

5/8 in.

12 ft.

Every

For oil carry-over

control4 suggested

upgrades:

Year

3/4 in. 15 ft.

BASIC test acceptable

range:

3 oil units

per month.

See

appendix

For the Bendix® BASIC™ Test Kit,

order

Bendix

P/N

5013711

BASIC test acceptable

range:

5 oil units

per month.

See

appendix

Bendix

Footnotes:

1 With increased air demand, the air dryer cartridge needs to be replaced more often. 2 Use the drain valves to slowly drain all reservoirs to zero psi. 3 Allow the oil/water mixture to fully settle before measuring oil quantity. 4 To counter above normal temperatures at the air dryer inlet, (and resultant oil-vapor passing

upstream in the air system) replace the discharge line with one of a larger diameter and/

or longer length. This helps reduce the air's temperature. If sufcient cooling occurs, the

oil-vapor condenses and can be removed by the air dryer. Discharge line upgrades are not covered under warranty. Note: To help prevent discharge line freeze-ups, shorter

discharge line lengths or insulation may be required in cold climates. (See Bendix Bulletins TCH-008-021 and TCH-008-022, available on www.bendix.com.)

5 For certain vehicles/applications, where turbo-charged inlet air is used, a smaller size

compressor may be permissible.

Note: Compressor and/or air dryer upgrades are recommended in cases where duty cycle is greater than the normal range (for the examples above).

For Bendix® Tu-Flo® 550 and 750 compressors, unloader service is

recommended every 250,000 miles.

Air Brake Charging System Troubleshooting

How to use this guide:

Find the Symptom(s) that you see, then move to the right to nd the possible causes (“What it may indicate”) and

remedies (“What you should do”).

Review the warranty policy before performing any intrusive compressor maintenance. Unloader or cylinder head gasket replacement and resealing of the bottom cover plate are usually permitted under warranty. Follow all standard safety procedures when performing any maintenance.

GENERAL SAFETY GUIDELINES

WARNING! PLEASE READ AND FOLLOW THESE INSTRUCTIONS

When working on or around a vehicle, the following guidelines should be observed AT ALL TIMES:

▲ Park the vehicle on a level sur face, apply the

parking brakes and always block the wheels. Always wear personal protection equipment.

▲ Stop the engine and remove the ignition key

when working under or around the vehicle.

When working in the engine compartment,

the engine should be shut off and the ignition

key should be removed. Where circumstances

require that the engine be in operation, EXTREME CAUTION should be used to prevent personal

injury resulting from contact with moving,

rotating, leaking, heated or electrically-charged components.

▲ Do not attempt to install, remove, disassemble

or assemble a component until you have read, and thoroughly understand, the recommended procedures. Use only the proper tools and observe all pr ecautions pertainin g to use of those tools.

▲ If the work is being performed on the vehicle’s

air brake system, or any auxiliary pressurized air systems, make certain to drain the air pressure from all reservoirs before beginning ANY work on the vehicle. If the vehicle is equipped with a

Bendix

AD-IS® air dryer system, a Bendix® DRM™ dryer reser voir module, or a Bendix® AD-9si™ air dryer, be sure to drain the purge reservoir.

▲ Following the vehicle manufacturer’s

recommended procedures, deactivate the electrica l system in a manner that safely removes all electrical power from the vehicle.

▲ You should consult the vehicle manufacturer's operating and service manuals, and any related literature,

in conjunction with the Guidelines above.

TO AVOID PERSONAL INJURY OR DEATH:

Look for:

Normal - Charging system is working within normal range.

Check - Charging system needs further investigation.

▲ Never exceed manufacturer’s recommended

pressures.

▲ Never connect or disconnect a hose or line

containing pressure; it may whip. Never remove a component or plug unless you are cer tain all system pressure has been depleted.

▲ Use only genuine Bendix

parts, components and kits. Replacement

hardware, tubing, hose,  ttings, etc. must be of

equivalent size, type and strength as original

equipment and be designed speci cally for such

applications and systems.

▲ Components with stripped threads or damaged

parts should be replaced rather than repaired. Do not attempt repairs requiring machining or

welding unless speci cally stated and approved

by the vehicle and component manufacturer.

▲ Prior to returning the vehicle to service, make

certain all components and systems are restored to their proper operating condition.

▲ For vehicles with Automatic Traction Control

(ATC), the ATC function must be disabled (ATC indicator lamp should be ON) prior to pe rforming any vehicle maintenance where one or more wheels on a drive axle are lifted off the ground and moving.

▲ The power MUST be temporarily disconnected

from the radar sensor whenever any tests USING A DYNAMOMETER are conducted on a Bendix

Wingman® Advanced™-equipped vehicle.

brand replacement

Symptom: What it may indicate: What you should do:

1.0 Oil Test Card results

Not a valid test.





Bendix® BASIC™ Test use this cup to

Discontinue using this test. Do not use this card test to diagnose compressor "oil passing" issues. They are subjective and error prone. Use only the Bendix Air System Inspection Cup (BASIC) test and the methods described in this guide for advanced troubleshooting.

The Bendix BASIC test should be the

denitive method for judging excessive

oil fouling/oil passing. (See Appendix, on page 17 for a flowchart and expanded explanation of the checklist used when conducting the BASIC test.)

measure

"oil units"

Symptom: What it may indicate: What you should do:

2.0 Oil on the outside of the compressor

2.1 Oil leaking at compressor / engine connections:

2.2 Oil leaking from compressor:

Engine and/or other accessories leaking onto compressor.

(a)Leak at the front or rear (fuel

pump, etc.) mounting ange.

(b) Leak at air inlet tting.

(d) Loose/broken oil line ttings.

(a) Excessive leak at head gasket.

(b) Leak at bottom cover plate.

(d) Leak through crankcase.

Find the source and repair. Return the vehicle to service.

Repair or replace as necessary. If the

mounting bolt torques are low, replace the gasket.

Replace the tting gasket. Inspect inlet hose

and replace as necessary.

Replace gasket or tting as necessary to

ensure good seal.

Inspect and repair as necessary.

Go to Test 1 on page 14.

Reseal bottom cover plate using RTV

silicone sealant.

Replace compressor.

(a)



3.0 Oil at air dryer purge/exhaust or surrounding Area

If unable to tell source of leak.

Head gasket (a)

and rear ange



gasket (c)

(c)

Air brake charging system functioning normally.

locations.

Clean compressor and check periodically.

Air dryers remove water and oil from the air

brake charging system.

Check that regular maintenance is being

performed. Return the vehicle to service. An optional kit (Bendix piece number 5011327 for the Bendix® AD-IS® or AD-IP® air dryers, or 5003838 for the Bendix® AD-9® air dryer) is available to redirect the air dryer exhaust.

Symptom: What it may indicate: What you should do:

4.0 Oil in supply or service reservoir (air dryer installed)

(If a maintained Bendix® PuraGuard® system lter or Bendix® PuraGuard®

oil coalescing lter

is installed, call 1-800-AIR-BRAKE (1-800-247-2725) option 2 and speak to a Tech

Team member.)

See Table A, on page 3, for maintenance schedule information.

Maintenance

(a) If air brake charging system

maintenance has not been performed.

That is, reservoir(s) have not been

drained per the schedule in Table A on page 3, Column 4, and/or the air dryer maintenance has not been performed as in Column 3.

(b) If the vehicle maintenance has

been performed as recommended in Table A on page 3, some oil in the reservoirs is normal.

(a)

Drain all air tanks (reservoirs) into the Bendix® BASIC™ test cup. (Bendix kit P/N 5013711).

Duty cycle too high

Drain all air tanks and check the vehicle

at next service interval using the Bendix® BASIC test. See Table A on page 3, column 3 and 4, for recommended service schedule.

Drain all air tanks into Bendix BASIC test

cup (Bendix Air System Inspection Cup).

If less than one unit of reservoir contents

is found, the vehicle can be returned to service. Note: If more than one oil unit

of water (or a cloudy emulsion mixture) is present, change the vehicle's air dryer, check for air system leakage (Test 2, on page 14), stop the inspection and check again at the next service interval.

See the BASIC test kit for full details.

If less than one "oil unit" of water (or water/

cloudy emulsion mixture) is present, use the BASIC cup chart on the label of the cup to determine if the amount of oil found is within the acceptable level.

 If within the normal range, return the

vehicle to service. For vehicles with accessories that are sensitive to small amounts of oil, consider a Bendix® PuraGuard® oil coalescing lter.

 If outside the normal range go to

Symptom 4.0(c).

Also see Table A on page 3, Column

3 for recommended air dryer cartridge replacement schedule.

(d) Compressor may be undersized

for the application.

The duty cycle is the ratio of time the compressor spends building air to total engine running time. Air compressors are designed to build air (to "run loaded") up to 25% of the time. Higher duty cycles cause conditions that affect air brake charging system performance which may require additional maintenance. Factors that add to the duty cycle are: air suspension, additional air accessories, use of an undersized compressor, frequent stops, excessive leakage

from ttings, connections, lines, chambers or valves, etc.

Go to

Test 2 on page 14.

See Table A Column 1, on page 3 for

recommended compressor sizes.

If the compressor is "too small" for the

vehicle's role (for example, where a vehicle's use has changed or service conditions exceed the original vehicle or engine OE spec's) then upgrade the compressor. Note: The costs incurred (e.g. installing a larger capacity compressor, etc.) are not covered under original compressor warranty.

If the compressor is correct for the

vehicle, go to Symptom 4.0 (e).

Symptom: What it may indicate: What you should do:

4.0 Oil in supply or service reservoir* (air dryer installed)

(continued)

(g)

Testing the temperature

at the discharge tting.

(g)

Kinked discharge line shown.

Temperature

(e) Air compressor discharge and/

or air dryer inlet temperature too high.

(f) Insufcient coolant ow.

(f)(e)

Inspecting the coolant hoses.

(g) Restricted discharge line.

Check temperature as outlined in Test 3 on

page 14. If temperatures are normal go to

4.0(h).

Inspect coolant line. Replace as necessary

(I.D. is 1/2").

Inspect the coolant lines for kinks and

restrictions and ttings for restrictions.

Replace as necessary.

Verify coolant lines go from engine block to

compressor and back to the water pump. Repair as necessary.

If discharge line is restricted or more than

1/16" carbon build up is found, replace the discharge line. See Table A, column 2, on page 3 for recommended size. Replace as necessary.

The discharge line must maintain a

constant slope down from the compressor

to the air dryer inlet tting to avoid low points where ice may form and block the ow.

If, instead, ice blockages occur at the air dryer inlet, insulation may be added here,

or if the inlet tting is a typical 90 degree tting, it may be changed to a straight or 45 degree tting. For more information on

how to help prevent discharge line freezeups, see Bendix Bulletins TCH-008-021 and TCH-008-022. Shorter discharge line lengths or insulation may be required in cold climates.

(h)

Other

(h) Restricted air inlet (not enough air

to compressor).

Check compressor air inlet line for

restrictions, brittleness, soft or sagging hose conditions etc. Repair as necessary. Inlet line size is 3/4 ID. Maximum restriction requirement for compressors is 25 inches of water.

Check the engine air lter and service if

Partly collapsed inlet line shown.

*If a maintained Bendix® PuraGuard® system lter or Bendix® PuraGuard® oil coalescing lter is installed, call 1-800-AIR-BRAKE (1-800-247-2725) option 2 and speak to a Tech Team member.

necessary (if possible, check the air lter

usage indicator).

Symptom: What it may indicate: What you should do:

4.0 Oil in supply or service reservoir* (air dryer installed

Other (cont.)

(i) Poorly ltered inlet air (poor air

quality to compressor).

(continued)

(j) Governor malfunction or setting.

(k) Compressor malfunction.

Crankcase Flooding Consider installing a compressor bottom drain kit

(where available) in cases of chronic oil passing where all other operating conditions have been investigated. Bendix® compressors are designed to have a 'dry' sump and the presence of excess oil in the crankcase can lead to oil carryover.

Check for leaking, damaged or defective

compressor air inlet components (e.g.

induction line, ttings, gaskets, lter bodies,

etc.). Repair inlet components as needed.

Note: Dirt ingestion will damage compressor and is not covered under warranty.

Inspect the engine air cleaner.

Go to Test 4 on page 15.

If you found excessive oil present in the

service reservoir in step 4.0 (b) above and

you did not nd any issues in steps 4.0 (c)

through 4.0 (j) above, the compressor may be passing oil.

Replace compressor. If still under warranty,

follow normal warranty process. Note: After

replacing a compressor, residual oil may take a considerable period of time to be

ushed from the air brake system.

*If a maintained Bendix® PuraGuard® system lter or Bendix® PuraGuard® oil coalescing lter is installed, call 1-800-AIR-BRAKE (1-800-247-2725) option 2 and speak to a Tech Team member.

5.0 Oil present at valves (e.g. at

Air brake system valves are required to tolerate a light coating of oil.

A small amount of oil does not affect SAE

J2024** compliant valves.

exhaust, or seen during servicing).

Check that regular maintenance is being

performed and that the amount of oil in the air tanks (reservoirs) is within the acceptable range shown on the Bendix® BASIC test cup (see also column 5 of Table A on page 3). Return the vehicle to service.

For oil-sensitive systems, see page 2.

** SAE J2024 outlines tests all air brake system

pneumatic components need to be able to pass, including minimum levels of tolerance to contamination.

Genuine Bendix valves are all SAE J2024 compliant.

Symptom: What it may indicate: What you should do:

6.0 Excessive oil consumption in engine.

7.0 Oil present at air dryer cartridge during maintenance.

8.0 Oil in ping tank or compressor discharge aftercooler.

9.0 Air brake charging system seems slow to build pressure.

A problem with engine or other engine accessory.

The engine service manual has more information.

Air brake charging system is functioning normally.

Oil shown leaking from an air dryer cartridge.

Air brake charging system is functioning normally.

(a) Air brake charging system

functioning normally.

(b) Air brake system leakage.

See engine service manual.

Air dryers remove water and oil from

the air brake charging system. A small amount of oil is normal. Check that regular maintenance is being performed and that the amount of oil in the air tanks (reservoirs) is within the acceptable range shown by the BASIC Test (see also column 5 of Table A on page 3). Replace the air dryer cartridge as needed and return the vehicle to service.

Follow vehicle OE maintenance

recommendation for these components.

Using dash gauges, verify that the

compressor builds air system pressure from 85-100 psi in 40 seconds or less with engine at full governed rpm. Return the vehicle to service.

Go to Test 2 on page 14.

for the application.

(d) Compressor unloader mechanism

malfunction.

(e) Damaged compressor head

gasket.

See Table A Column 1, on page 3 for some

typical compressor applications. If the compressor is "too small" for the vehicle's role, for example, where a vehicle's use has changed, then upgrade the compressor.

Note: The costs incurred (e.g. installing a larger capacity compressor, etc.) are not covered under original compressor warranty.

Go to Test 6 on page 15.

An air leak at the head gasket may

indicate a downstream restriction such as a freeze-up or carbon blockage and/or could indicate a defective or missing safety valve. Find blockage (go to 9.0(f) for details) and then replace the compressor. Do not reuse the safety valve without testing. See Symptom 12.0(a).

Symptom: What it may indicate: What you should do:

9.0 Air brake charging system seems slow to build pressure.

(continued)

Dash gauges.

(f) Restricted discharge line.

(f)

Kinked discharge line shown.

If discharge line is restricted:  By more than 1/16" carbon build up,

replace the discharge line (see Table A, column 2, on page 3 for recommended size) and go to Test 3 on page 14.

 By other restrictions (e.g. kinks). Replace

the discharge line. See Table A, column 2, on page 3 for recommended size. Retest for air build. Return vehicle to service or, if problem persists, go to

9.0(a).

The discharge line must maintain a

constant slope down from the compressor

to the air dryer inlet tting to avoid low points where ice may form and block the ow.

If, instead, ice blockages occur at the air dryer inlet, insulation may be added here,

or if the inlet tting is a typical 90 degree tting, it may be changed to a straight or 45 degree tting. For more information on

how to help prevent discharge line freezeups, see Bendix® Bulletins TCH-008-021 and TCH-008-022. Shorter discharge line lengths or insulation may be required in cold climates.

(g)

Partly collapsed inlet line shown.

(g) Restricted air inlet (not enough air

to compressor).

(h) Poorly ltered inlet air (poor air

quality to compressor).

(i) Compressor malfunction.

Check compressor air inlet line for

restrictions, brittleness, soft or sagging hose conditions etc. Repair as necessary. Refer to vehicle manufacturer’s guidelines for inlet line size.

Check the engine air lter and service if

necessary (if possible, check the air lter

usage indicator).

Check for leaking, damaged or defective

compressor air inlet components (e.g. induction line, fittings, gaskets, filter bodies, etc.). Repair inlet components as needed. Note: Dirt ingestion will damage

compressor and is not covered under warranty.

Replace the compressor only after making

certain that none of the preceding conditions,

9.0 (a) through 9.0 (h), exist.

Symptom: What it may indicate: What you should do:

10.0 Air charging system doesn’t build air.

* Note: For the Bendix® DuraFlo 596™ air compressor, not only the governor, but also the SV-1™ synchro valve used would need to be tested. See Bendix Bulletin TCH-001-048.

11.0 Compressor safety valve releases air

(compressor builds too much air).



(a) Governor malfunction*.

(b) Restricted discharge line.

exhaust port frozen open.

(d) Compressor malfunction.

(a) Restricted discharge line.

Damaged discharge line shown.

Go to Test 4 on page 15.

See 9.0(f).

Replace air dryer heater.

Replace the compressor only after making

certain the preceding conditions do not exist.

If discharge line is restricted:  By more than 1/16" carbon build up,

replace the discharge line (see Table A, Column 2, on page 3 for recommended size) and go to Test 3 on page 14.

 By other restrictions (e.g. kinks).

Replace the discharge line. See Table A, Column 2, on page 3 for recommended size.

The discharge line must maintain a

constant slope down from the compressor

to the air dryer inlet tting to avoid low points where ice may form and block the ow.

If, instead, ice blockages occur at the air dryer inlet, insulation may be added here,

or if the inlet tting is a typical 90 degree tting, it may be changed to a straight or 45 degree tting. For more information on

how to help prevent discharge line freezeups, see Bendix Bulletins TCH-008-021 and TCH-008-022. Shorter discharge line lengths or insulation may be required in cold climates.

(b) Downstream air brake system

check valves or lines may be blocked or damaged.

(d) Compressor safety valve

malfunction.

(e) Compressor unloader mechanism

malfunction.

(f) Governor malfunction.

Inspect air lines and verify check valves are

operating properly.

Ensure discharge line is installed into the

inlet of the air dryer and delivery is routed to the service reservoir.

Verify relief pressure is 250 psi. Replace if

defective.

Go to Test 6 on page 15.

Go to Test 4 on page 15.

Symptom: What it may indicate: What you should do:

12.0 Air dryer safety valve releases air.

Air dryer safety valve





Technician removes governor.

13.0 Reservoir safety valve releases air

(a) Restriction between air dryer and

reservoir.

(b) Air dryer safety valve malfunction.

performed.

(d) Air dryer malfunction.

(e) Improper governor control line

installation to the reservoir.

(f) Governor malfunction.

(a) Reservoir safety valve malfunction.

(b) Governor malfunction.

Inspect delivery lines to reservoir for

restrictions and repair as needed.

Verify relief pressure is at vehicle or

component manufacturer specications.

Replace if defective.

See Maintenance Schedule and Usage

Guidelines (Table A Column 3, on page 3).

Verify operation of air dryer. Follow vehicle

O.E. maintenance recommendations and component Service Data information.

Go to Test 5 on page 15.

Go to Test 4 on page 15.

Verify relief pressure is at vehicle or

component manufacturer's specications

(typically 150 psi). Replace if defective.

Go to Test 4 on page 15.

14.0 Air dryer doesn’t purge.

(Never hear exhaust from air dryer.)

15.0 Compressor constantly cycles

(compressor remains unloaded for a very short time.)

malfunction.

(a) Air dryer malfunction.

(b) Governor malfunction.

(d) Improper governor control line

installation to the reservoir.

(a) Air brake charging system

maintenance not performed.

(b) Compressor unloader mechanism

malfunction.

check valve malfunction.

Go to Test 6 on page 15.

Verify operation of air dryer. Follow vehicle

OE maintenance recommendations.

Go to Test 4 on page 15.

Go to Test 2 on page 14.

Go to Test 5 on page 15.

Available reservoir capacity may be

reduced by build up of water etc. Drain and perform routine maintenance per Table A, columns 3 & 4, on page 3.

Go to Test 6 on page 15.

Verify operation of air dryer. Follow vehicle

OE maintenance recommendations and component Service Data information.

(d) Air brake system leakage.

Go to Test 2 on page 14.

Symptom: What it may indicate: What you should do:

16.0 Compressor leaks air

Testing for leaks with soap solution.

17.0 Compressor leaks coolant

(a) Compressor leaks air at

connections or ports.

(b) Compressor unloader mechanism

malfunction.

gasket.

Head

gasket

location



(a) Improperly installed plugs or

coolant line ttings.

(b) Damaged compressor head

gasket.

Check for leaking, damaged or defective

compressor ttings, gaskets, etc. Repair

or replace as necessary.

Go to Test 6 on page 15.

An air leak at the head gasket may indicate

a downstream restriction such as a freezeup or carbon blockage and/or could indicate a defective or missing safety valve. Find blockage (go to 9.0(f) for details) and then replace the compressor. Do not re-use the safety valve without testing. See Symptom

12.0(a).

Inspect for loose or over-torqued ttings.

Reseal and tighten loose ttings and plugs as necessary. If over-torqued ttings and

plugs have cracked ports in the head, replace the compressor.

An air leak at the head gasket may indicate

a downstream restriction such as a freezeup or carbon blockage and/or could indicate a defective, or missing, safety valve. Find blockage (go to 9.0(f) for details) and then replace the compressor. Do not re-use the safety valve without testing. See Symptom

12.0(a).

18.0 Noisy compressor

(multi-cylinder compressors only)

This guide attempts to cover most compressor system problems. Here are some rare sources of problems not covered in this guide:

• Turbocharger leakage. Lubricating oil from leaking turbocharger seals can enter the air compressor intake and give misleading symptoms.

(a) Damaged compressor.

Other Miscellaneous Areas to Consider

• Where a compressor does not have a safety valve installed, if a partial or complete discharge line blockage has occurred, damage can occur to the connecting rod bearings. Damage of this kind may not be detected and could lead to compressor problems at a later date.

If casting porosity is detected, replace the

compressor.

Replace the compressor.

Tests

Test 1: Excessive Oil Leakage at the Head Gasket

Exterior leaks at the head gasket are not a sign that oil is being passed into the air charging system. Oil weepage at the head gasket does not prevent the compressor from building air.

Observe the amount of weepage from the head gasket. If the oil is only around the cylinder head area, it is acceptable (return the vehicle to service), but, if the oil weepage extends down to the nameplate area of the compressor, the gasket can be replaced.

Test 2: Air Brake System and Accessory Leakage

LOOK

FOR

WEEPAGE

Inspect for air leaks when working on a vehicle and repair them promptly. Park the vehicle on level ground and chock wheels. Build system pressure to governor cut-out and allow the pressure to stabilize for one minute.

If you see any noticeable decrease of the dash air gauge readings (i.e. more than 4 psi, plus two psi for each additional trailer) during either two minute test,

repair the leaks and repeat this test to conrm that

they have been repaired.

Step 1: Observe the dash gauges for two additional minutes without the service brakes applied. Step 2: Apply the service brakes and allow the pressure to stabilize. Continue holding for two

Air leaks can also be found in the charging system, parking brakes, and/or other components - inspect

and repair as necessary. minutes (you may use a block of wood to hold the pedal in position.) Observe the dash gauges.

Test 3: Air Compressor Discharge Temperature and Air Dryer Inlet Temperature*

(* Note that only vehicles that have passed Test 2 would be candidates for this test.)

Caution: The temperatures used in this test are not normal vehicle conditions. Above normal temperatures can cause oil (as vapor) to pass through the air dryer into the air brake system.

This test is run with the engine at normal operating temperature, with engine at max. rpm. If available, a dynamometer may be used.

1. Allow the compressor to build the air system pressure to governor cut-in.

2. Pump the brakes to bring the dash gauge pressure to 90 psi.

3. Allow the compressor to build pressure from 95 to 105 psi gauge pressure and maintain this pressure range by cycling the brakes for

ve (5) minutes.

Discharge Line

4. Then, while maintaining max rpm and pressure

range, measure and record the surface temperature of the ttings:

 at the compressor discharge port. (T1).  at the air dryer inlet tting. (T2).

Use a touch probe thermocouple for measuring

the temperature.

5. See table below.

6. Retest before returning the vehicle to service.

T1 T2

Compressor Air Dryer

Discharge Inlet Fitting Fitting

under under Temperatures are within 360°F 200°F normal range for this test, check other symptoms. Go to 4.0 (h).

under over This could indicate a discharge 360°F 200°F line problem (e.g. restriction). Call 1-800-AIR-BRAKE (1-800-247-2725) option 2 and speak with our Tech Team.

over __ Compressor is running hot. 360°F Check coolant 4(f) and/or discharge line 4(g).

Action

Tests (continued)

Test 4: Governor Malfunction

1. Inspect control lines to and from the governor for restrictions (e.g. collapsed or kinked). Repair as necessary.

2. Using a calibrated external gauge in the supply reservoir, service reservoir, or reservoir port of the Bendix® D-2® governor, verify cut-in and cut-out pressures are within vehicle OEM

specication.

Test 5: Governor Control Line

1. Ensure that the governor control line from the reservoir is located at or near the top of the reservoir. (This line, if located near the bottom of the reservoir, can become blocked or restricted by the reservoir contents e.g. water or ice.)

Test 6: Compressor Unloader Leakage

Bendix® Compressors: Park vehicle, chock wheels, and follow all standard safety procedures. Remove

the governor and install a tting to the unloader

port. Add a section of air hose (min 1 foot long

for a 1/2" diameter line) and a gauge to the tting

followed by a shut-off valve and an air source (shop air or small air tank). Open the shut off and charge the unloader port by allowing air pressure to enter

3. If the governor is malfunctioning, replace it.

2. Perform proper reservoir drain intervals and air dryer cartridge maintenance per Maintenance Schedule and Usage Guidelines (Table A on page 3).

3. Return the vehicle to service.

the hose and unload the compressor. Shut off the air supply and observe the gauge. A steady reading indicates no leakage at the unloader port, but a falling reading shows that the unloader mechanism is leaking and needs to be serviced. See Bendix Technical Bulletin TCH-001-060 for more information on unloader pistons

NOTES

Appendix: Information about the Bendix® BASIC™ Test Kit (Bendix P/N 5013711)

Bendix® Air System Inspection Cup

(BASIC) Test Information

Oil

Units

Cup

Replace the Compressor. If under warranty, follow standard procedures.

If, after a compressor was already replaced, the vehicle fails the BASIC test again, do not replace the compressor**** - use the Advanced Troubleshooting Guide to investigate the cause(s).

* If the number of days since the air tanks were drained is unknown

- use the 30 day line.

** Note: Typical air dryer cartridge replacement schedule is every 3 yrs/ 300K miles for low air use vehicles and every year/100K miles for high air use vehicles.

*** To get an accurate reading for the amount of oil collected during a 30 day period, ask the customer not to drain the air tanks before returning. (Note that 30-90 days is the recommended air tank drain schedule for vehicles equipped with a Bendix air dryer that are properly maintained.) If, in cold weather conditions, the 30 day air tank drain schedule is longer than the customer's usual draining interval, the customer must determine, based on its experience with the vehicle, whether to participate now, or wait for warmer weather. See the cold weather tips in Bendix® Bulletins TCH-008-021 and TCH-008-022.

****Note: After replacing a compressor, residual oil may take

a considerable period of time to be ushed from the air brake

system.

Appendix continued: Information about the BASIC Test Kit (Bendix P/N 5013711)

Filling in the Checklist for the Bendix® Air System Inspection Cup (BASIC) Test

Note: Follow all standard safety precautions. For vehicles using a desiccant air dryer.

The Service Writer lls out these elds with information gained from the customer

Number of Days Since Air Tanks Were Last Drained: ________ Date: ___________Vehicle #: ____________

Engine SN __________________________ Vehicle Used for: _______________Typical Load:________ (lbs.)

No. of Axles: ____ (tractor) ____ (trailer) No. of Lift Axles: ____ Technician’s Name: ____________________

Customer’s Complaint Have you conrmed complaint? (Please check all that apply)

Checklist for Technician

“Relay valve  leaks oil /  malfunctions” ........ no  yes*

The Service Writer also checks off any complaints that the customer makes to help the Technician in investigating.

“Dash valve  leaks oil /  malfunctions” ........ no  yes*

 “Air dryer leaks oil”......................... no  yes*

 “Governor malfunction” ..................... no  yes*

 “Oil in gladhands” ......................... no  yes*

how much oil did you nd? ________________________________

 “Oil on ground or vehicle exterior” ............ no  yes*

amount described: ______________________________________

 “Short air dryer cartridge life” replaces every: ______________  miles,  kms, or  months  “Oil in air tanks” amount described:_______________________

We will measure amount currently found when we get to step B of the test.

 “Excessive engine oil loss” amount described: ______________

Is the engine leaking oil? .................... no  yes*

Is the compressor leaking oil? ................. no  yes*

 Other complaint:

_____________________________________

 No customer complaint.

BASIC test starts here:

STEP A - Select one:

 This is a low air use vehicle: Line haul (single trailer) with 5 or less axles, or  This is a high air use vehicle: Garbage truck, transit bus, bulk unloader, or line

haul with 6 or more axles.

Then go to Step B.



The Technician checks boxes for any of the complaints that

can be conrmed.

*Note: A conrmed complaint

above does NOT mean that the compressor must be replaced. The full BASIC test below will investigate the facts.

The Technician selects the air

use category for the vehicle.

This decides which of the two

acceptance lines on the cup will be

used for the test below.

STEP B - Measure the Charging System Contents

1. Park and chock vehicle on level ground. Drain the air system by pumping the service brakes.

2. Completely drain ALL the air tanks into a single BASIC cup.

3. If there is less than one unit of contents total, end the test now and

return the vehicle to service. Vehicle passes.

4. If more than one oil unit of water (or a cloudy emulsion mixture) is found:

(a) Change the vehicle’s air dryer cartridge

- see Footnote 1, (b) Conduct the 4 minute leakage test (Step D),

Oil

Units

Otherwise, go to Step C.

Footnotes:

1 Typical air dryer cartridge replacement schedule is every 3 yrs/ 300K miles for low air use vehicles and every year/100K miles for high air use

vehicles.

2 To get an accurate reading for the amount of oil collected during a 30 day period, ask the customer not to drain the air tanks before returning. (Note

that 30-90 days is the recommended air tank drain schedule for vehicles equipped with a Bendix air dryer that are properly maintained.) If, in cold weather conditions, the 30 day air tank drain schedule is longer than the customer's usual draining interval, the customer must determine, based on its experience with the vehicle, whether to participate now, or wait for warmer weather. See the cold weather tips in Bendix® Bulletins TCH-008-021 and TCH-008-022.

STOP + CK.

Note for returning vehicles that are being retested after a water/cloudy emulsion mixture was found last time and the air dryer cartridge replaced: If more than one oil unit of water or a cloudy emulsion mixture is found again, stop the BASIC test and consult the air dryer's Service Data sheet troubleshooting section.

For an accurate test, the contents of all the air tanks on the vehicle should be used.

Appendix continued: Information about the BASIC Test Kit (Bendix P/N 5013711)

Filling in the Checklist for the Bendix® Air System Inspection Cup (BASIC) Test

Note: Follow all standard safety precautions. For vehicles using a desiccant air dryer.

STEP C - How to Use the BASIC Test

The Technician uses the chart (label) on the BASIC test cup to help decide the action to take, based on the amount of oil found. Use the lower acceptance line for low air use vehicles, and upper line for high air use vehicles (from Step A).

1. Record days since air tanks were last drained.

_________ days _________ units

If number of days is:

30-60 days (high air

30-90 days (low air use)

Otherwise . . .

(if the number of days is unknown, or outside the



use) or



limits above)

if oil level is at or below

the acceptance line for

number of days if oil level is above

acceptance line for number

if oil level is at or below

30-day acceptance line 

if oil level is above 30-day

acceptance line 

BASIC Test Example

An oil level of 4 units in a sixty-day period is within the acceptance area (at or below the line) for both low and high air use vehicles. Return the vehicle to service.

The Technician looks for the point where the number of days since the air tanks were drained meets the oil level. If it is at or below the (low or high use) acceptance line, the vehicle has passed the test. If

Sixty days since last air

tank draining

the point is above the line, we go to the leakage test.

STEP D - Air Brake System Leakage Test

Park the vehicle on level ground and chock wheels. Build system pressure to governor cut-out and allow the pressure to stabilize for one minute.

1: Observe the dash gauges for two additional minutes without the service brakes applied.

2: Apply service brakes for two minutes (allow pressure to stabilize) and observe the

dash gauges.

If you see any noticeable decrease of the dash air gauge readings repair leaks. Repeat

this test to conrm that air leaks have been repaired and return vehicle to service. Please

repeat BASIC test at next service interval. Note: Air leaks can also be found in the charging system, parking brakes, and/or other components - inspect and repair as necessary.

2. Record amount of oil found:



of days 

Acceptance

Lines

Decision point

Air leakage is the number one cause of compressors having to pump excessive amounts of air, in turn run too hot and pass oil vapor along into the system. Here the Technician conducts a four-minute test to see if leakage is a problem with the vehicle being tested.

3. Action to take



System OK. Return to service.

Go to Step D

System OK. Return to service.

Stop inspection. Test again after 30 days. See Footnote 2.

Oil

Level

STOP TEST

STOP

+ CK.

If no air leakage was detected, and if you are conducting this

test after completing Step C, go to Step E.

STEP E - If No Air Leakage Was Detected In Step D

Replace the compressor.

Note: If the compressor is within warranty period, please follow standard warranty procedures. Attach the completed checklist to warranty claim.

The Technician only reaches Step E if the amount of oil found, for the amount of time since the air tanks were last drained exceeds the acceptance level, AND the vehicle passes the four-minute leakage test (no noticeable leakage was detected).

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Bendix Commercial Vehicle Systems TROUBLE SHOOTING COMPRESSOR User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual