McQuay ST010 Installation Manual

GENERAL

The Model ST air cooled condensing units are com­plete assemblies, factory tested and shipped with a

Refrigerant 22 holding charge. They have been de­signed to operate in conjunction with remote direct
expansion evaporator(s) and are available for operation
on three phase power supplies (see the published
catalog data for power ratings available). All units have

115 volt control circuits with provision for connection

of a remote mounted 24 volt thermostat. Additional

information on the units is covered on the pages

following.

McQUAY

RESPONSIBILITIES

The Model ST condensing units when applied within

the performance and application limits specified on the

sales and installation data will provide safe and

dependable service.

Details on the Model ST product warranty are included
in the information envelope packed with the unit.

RECEIVING EQUIPMENT

1. CHECK EQUIPMENT before removing it from the
delivery vehicle. The unit nameplate (shown below)

indicates the unit model number, power character­istics, serial number, etc. Be sure to check the
nameplate data against the shipping papers and pay
particular attention to the unit model number (size)
and power characteristics.

2.3.INSPECT the unit while it is still on the delivery
vehicle, make a note of any damage on the delivery
receipt. Be sure to carefully check for hidden
damage. If damage is found, have it checked and
noted by the representative of the transportation
company before accepting or removing the unit
from the vehicle.

NOTE

All equipment furnished by McQuay is
shipped F.O.B. the factory and all claims
for handling and shipping damage are the
responsibility of the consignee.

If an item is missing from the shipment notify your
nearest McQuay Sales office.

RIGGING - The STO08, 010, 013, and 015 should
be lifted by the skid, the ST020, 025, and 030 from
the lifting holes at the base corners. When lifting
use a spreader bar to prevent damage. If the unit is
to be skidded, be sure an adequate number of
rollers are used and be careful when moving the
unit not to drop it. Under no circumstances should
the unit be dragged with or without the skid.

NOTE

Unit mounting legs are shipped in a sepa­rate carton and are located in the compres­sor compartment. Before setting the unit at
its final location, attach the support legs at
each corner with the bolts provided.

5/8”
anchor holes are provided in the legs for
securing the unit to its base.

When requesting information about this
unit please forward the unit model number,
style and serial numbers with your inquiry.

UNIT MODEL NUMBER INTERPRETATION

ST 020 A

PRODUCT
FAMILY

NOMINAL
CAPACITY-TONS

CONDENSING MEDIUM
A = AIR

J

2 s 00

SPECIAL
MODIFICATIONS

UNIT POWER
CHARACTERISTICS

DESIGN MODIFICATION

CLEARANCES

The unit has been designed to permit slab or roof
mounting and care must be taken to provide adequate
clearance for air flow in and out of the unit.

TOP CLEARANCE - The unit has a draw through air
circuit with vertical air discharge from the top of the

unit. It is important that the areas above and below are
clear of any obstructions that could impede or divert
the air flow and cause recirculation back to the air

inlet.

SIDE CLEARANCE - A minimum clearance of 36

inches is required with the exception of the compres-

sor access end of the unit, where 42 inches is

recommended.

VIBRATION ISOLATION

Internal
isolation of the fan motors generally make it unneces-

sary to provide additional vribration isolation for the

unit. However, additional isolation could be required
depending on the installation location and building
construction.

Wherever possible locate the unit away from or over

occupied areas and provide adequate piping isolation.
Be
where it passes through walls, roof or floors.

spring

mounting of the compressor and

careful

not to allow piping to touch the structure

2

TABLE 1

ST008,010,013

ST020,025,030

m]

AND 015

REFRIGERANT PIPING

Piping between the condensing unit and the cooling

coil must be designed and installed to minimize

pressure drop, prevent liquid refrigerant carryover to

the compressor and to assure a continuous return of

compressor oil from the system. Piping sketches and
tables are not intended to provide information on all of
the possible arrangements. For example, when dual

circuit evaporators are used with an unloading com-

UNIT WEIGHT

Unit

Size

ST008

STDlO

ST013
ST015

ST020

ST025

-4

ST630 453

1

180
190
145
150

394
421

Gorn*r

1

2 f

I

210

465 277 270

aide.

I

-

POUNDS

3

I

115

0

4’

110

W&&t

I

Tti

615
645
745
775

1230
1365
1465

pressor, two liquid line solenoid valves may be used to
reduce coil capacity with compressor unloading. Note

especially that dual circuit evaporators should not be

piped with common liquid and suction lines to more

than one compressor. Separate evaporators, evapora­tor circuits and piping must be run for each compres­sor.

TABLE 2

SUCTION AND LIQUID LINE SIZES FOR EACH COMPRESSOR

MAXIMUM EQUIVALENT FEET OF COPPER TUBING

-

NOTES

Equivalent line lengths shown in above table are suitable for unit operating
condenser entering air temperature of 95F. When design conditions vary the table values should be rechecked.

0

Compressors used in the ST008 and 020 have no capacity reduction.

@

The compressors used in the

@

When refrigerant required to charge a circuit exceeds the pump down capacity of that circuit the use of a separate refrigerant storage
receiver will be required. The pump down capacity is based on the condenser 80% full at

@

Wherever vertical rise occurs in the piping, the minimum tonnage for oil entrainment should be checked and where necessary double
suction risers should be utilized. See Table 4, page 4.

@

Total equivalent feet for a given piping layout must include the equivalent length of straight pipe for fittings, valves and specialties added
to the total run of straight pipe.

ST010,

013, 015,025 and 030 have a single 50% capacity reduction step.

-

conditions

between 40 and 45F saturated suction temperature and

8OF.

3

TABLE 3

EQUIVALENT FEET OF STRAIGHT TUBING FOR COPPER

16 20

10 14
25 32
08 09

22

ws

_.qQtq":?&qt

14

0.9
23
07

TABLE 4

Minimum Tonnage (R-22)

To Carry Oil Up Suction Riser

NOTE. When compressor minimum tonnage is less than shown in the

above table for a given line size, double suction risers will be
required.

To preclude potential problems that could be traced to

piping,

standard accepted piping practices as de-

scribed below and in the ASHRAE handbooks are

recommended.

Piping recommendations include:

The use of type K or L clean copper tubing. All
joints should be thoroughly cleaned and brazed
with high temperature solder.

Piping sizes should be based on temperature/
pressure limitations as recommended in the follow­ing paragraphs. Under no circumstances should
pipe size be based upon the coil or condensing unit
piping connection size.

Suction line piping pressure drop should not exceed
the pressure equivalent of

2’F

per 100 feet of

equivalent pipe length. After the suction line size

has been determined, the vertical suction risers

should be checked to verify that oil will be carried

up the riser and back to the compressor. The

suction

line(s)

should be pitched in the direction of
refrigerant flow and adequately supported. Lines
should be free draining and fully insulated between
the evaporator(s) and the compressor. Table 2,
page 3 shows piping information for units operating
at suction temperatures between 40 and 45 and a
condenser entering air temperature of 95. If operat­ing conditions are expected to vary substantially
from these operating levels, the pipe sizing should
be rechecked.

Vertical suction risers should be checked using
Table 4, page 4 to determine the minimum tonnage
required to carry oil up suction risers of various
sizes.

I

26 33

17

41

13

I 29

2.3

5.6

1.7

I

38

FlTTlNGS AND

I

4.0

2.6
63

2.1

I

43

VALVES

5.0 6.0

3.3
82

2.6 3.2

55

I

I

69

5. The liquid line should be sized for a pressure drop
not to exceed the pressure equivalent of
saturated temperature. The liquid

line(s)

on all units
must include a liquid solenoid valve wired into the
circuit as shown on the applicable unit wiring
diagrams. The valve must be connected as follows:

1.

On model ST008, 010, 013, and 015 the solenoid

must be wired between terminals “P and N.”

2. Models ST020, 025, and 030 will require two sole

noid

valves, one in each liquid line. Make wiring
connections between terminals “P and N” for
circuit number 1 and “PI and N1" for circuit

number 2.

The unit control circuit for all compressors has been
designed to include a one time pump down cycle.
The use of a liquid line solenoid is required for

proper unit operation. In addition, a filter/drier
should be located between the liquid line service
valve and the solenoid valve and a combination

moisture indicator/sight glass should be located in
the liquid line ahead of the expansion valve.

6. Suggested piping arrangements are shown on page

5.

All

multiple compressor units require a separate

refrigerant circuit for each compressor.

7. If Dual Suction Risers are Used:
A.

The combined cross sectional areas of the two
risers must be capable of maintaining adequate
refrigerant velocity for oil return at full unit
tonnage.

B.

The extra risers should be of a smaller diameter
than the main riser. The extra riser must
include its own trap at the bottom and should
enter the main suction header at twelve o’clock.

C.

The trap serving the extra riser must be as short
as fittings permit. A “U” fitting or the combina­tion of a

90’

standard

ell

and a

90’

street

recommended.

D.

The suction line leaving the coil should also
include a trap if the expansion valve control bulb
is to be on the horizontal section leaving the coil
outlet. See the piping sketches on page 5.

4

4.1

10.0

ell

I

2’F

is

LEAK TESTING

All model ST condensing units are evacuated leak

tested and provided with a holding charge of R-22 at

the factory. Check the unit when it arrives at the job
site for damage or leaks in the refrigerant circuit. If the
refrigerant charge has been lost, locate and repair the
leak at the same time the connecting system is
checked. When you are ready to leak test, charge
enough R-22 into the system to raise the pressure to
about 30 psig; then add dry nitrogen and bring the

pressure up to a maximum of 150 psig. The system can
now be checked for leaks. Before attempting to repair

any leaks that may have been found, be sure to relieve

the test pressure from the system.

IMPORTANT CAUTION

Always use a pressure regulating valve on
the nitrogen drum and be sure to

nect the drum from the system after the
maximum of 150 psig test pressure is
reached. Under no circumstances should
you exceed the maximum leak test pressure
of 150 psig. DO NOT USE OXYGEN TO

BUILD UP PRESSURE, A SERIOUS EX­PLOSION COULD RESULT.

discon-

EVACUATION

After all leaks have been repaired the system can be
evacuated, proceed as follows:

Connect a good quality manometer or gauge
(capable of measuring one millimeter of vacuum)
into the system and locate it as far away as possible

from the vacuum pump.
The triple evacuation method is recommended.

Evacuate the system to 29” vacuum, then add enough
R-22 to break the vacuum and bring the system up to
10 psig pressure. Repeat this evacuation ‘two more
times and on the third evacuation break the vacuum by
feeding R-22 into the system through the gauge port
on the condenser liquid shut off valve. With the
refrigerant cylinder up ended, it should be possible to
install close to 75% of the required charge into the
system in this manner without starting the com-
pressor. Do not start the compressor until the
following checks have been made.

PRELIMINARY CHECKS BEFORE
STARTING COMPRESSOR(S)

1.

With the unit disconnect switch off, check to be
sure that the starter contacts meet evenly and that

all operating starter parts move freely. Check that
the time delay fuses
are of the proper size.

2.

Open all refrigerant
charge, and liquid).

3.

With the thermostat
room thermostat below the design temperature.
Check that the air handling unit fans are rotating in
the proper direction.

in the unit disconnect switch

service valves (suction, dis-

in the “off” position, set the

Close the disconnect switch which energizes the

4.
crankcase heaters. These heaters must be ener-

gized 8 hours before attempting to start the
compressor(s).

Check that line voltage is within

5.
compressor nameplate voltage rating.

+ 10 percent of the

CHARGING

With the cylinder still up ended, charge as much

1.

refrigerant as possible into the system. When the

system will no longer accept refrigerant in this

manner, disconnect the drum from the liquid valve
and reconnect it to the gauge port on the suction
service valve.

Check the compressor oil level. If the oil level is

2.

over the top of the glass, be prepared when the
compressor starts to shut it down if sounds of liquid
pumping are evident.

Recheck that the suction, liquid and discharge line

3.

shut off valves are open. Close the unit disconnect
switch and set the room thermostat to call for
cooling.

With the compressor operating, continue to allow

4.

refrigerant to enter until the estimated charge has
been weighed in and/or the sight glass clears. At
this point, check the liquid line temperature leaving
the condenser, it should indicate 10 to 12 degrees
of subcooling.

Another method of checking the refrigerant charge
after the initial 75% has been added to the unit
would be to block the condenser coil until the head

pressure is built up to about 300 psig. Continue to
add refrigerant until the sight glass clears and 10 to

12 degrees subcooling is obtained.

Regardless of the method used to charge the unit,
refer to the charging and operating curves applica­ble to the unit involved and check operating
pressures against the curve values.

After about one hour of operation, check the compres­sor amperage being drawn. It should not exceed the

Full Load Amperes listed on the unit nameplate.

Also check that the combination sight glass/moisture
indicator is showing a dry condition. If moisture is
indicated, a refrigerant drier will have to be added into
the system.

TABLE 5

APPROXIMATE OPERATING CHARGE

FOR COMPRESSOR CIRCUIT

NOTE: Approximate charge includes evaporator coil, condensing

unit, liquid line drier and approximately 25 ft. of
liquid line per circuit. Refrigerant charging should be
performed as described under “Charging” on Page 6.

-

R-22, LBS

suction

and

6

TYPICAL SCHEMATIC WIRING FOR MODELS

ST 025 AND

030

FUSE ~

115V.

BUSSMAN

FUSE PRIMARY CON

TRANSFORMER BUSS

4AMP

TYPE

NEC CLASS 2

MDX

COB WkllNG

-

X2 SYS

ONLY.

ON~OFF

FUSE

2.5A

SEE NOTES, PAGE 13

schematic diagram
shown on page 16

BEHIND TERM

HOUSING

BLOCK

TYPE S

UNIT LAYOUT

REFERENCE DRAWING

Xl COMPRESSOR

598C686-SUB

6

OPTIONAL

EQUIPMENT

ACCESSORY ITEMS

LOW AMBIENT FAN SPEED CONTROL - By
adding an accessory fan speed control to the last
operating fan motor on all model ST008 through 015
units, the minimum operating ambient temperature as
shown on Table 6, page 7 can be reduced to

O’F for all

unit operating capacities. This control is a standard

accessory available from McQuay for field installation.
TIME DELAY RELAY - On two compressor units

(models ST020 through

030),

it may be desirable to
prevent simultaneous starting of both compressors on
a call for cooling. An accessory time delay relay is
available for field installation in the unit operating
control circuit. This relay will add a short time delay
and only allow one compressor to start at a time.

SUCTION LINE ACCUMULATOR - Some systems,
depending on line length, solenoid valve leakage, etc.,
may require the use of a suction line accumulator to
prevent damage to the compressor from liquid

carry-

CONTROL CIRCUIT OPERATION

Refer to the schematic diagram shown on page 16. A
single line voltage fused disconnect switch must be

field supplied in the wiring supplying power to the unit.

With the disconnect switch closed, power is supplied
to the primary of the control transformer located on

over when the compressor first starts. A standard
accessory accumulator with a liquid capacity of 31
pounds is available for field installation in the suction
line of each compressor circuit.

PRESSURE GAUGES - Are available in kit form for
field installation.

HOT GAS BYPASS - This accessory option is
available for field installation on units where the
minimum capacity step does not reduce sufficiently to
meet the minimum load requirement. The use of hot
gas bypass is recommended on systems where eva­porator air flow is varied or where the load at standard
air flow reduces sufficiently to cause a low suction

pressure condition. The kit contains all parts required
to adapt model ST units to hot gas bypass. It must be

used on systems with side outlet distributors on the

coil or on systems where it is permissible to introduce

hot gas between the expansion valve and evaporator

unit.

line 47, a secondary control voltage of 115 volts is

generated by the transformer.

A second transformer (115 to 24V) is located on line

74. On a call for cooling by either or both of the room

thermostats “1TC” or

relays

“1CR”

and “2CR”

2TC,”

on lines 78 and 80 are energized through the indoor

unit fan coil unit interlock contacts

(5MA).

15

Assume thermostat contacts

cooling, relay coil “ICR” contacts on lines 56 and 59

will be closed. Closing the

energize the compressor starter holding coil
through the high pressure cutout
switch
pressure cutout
gized, the contacts on lines I, 3 and 5 and auxiliary
contacts
sor number 1 and auxiliary contacts 1MA line 54 pro­vide an interlock circuit parallel to the
on line 56. A second set of
close and energize liquid line solenoid valve “1 LS”.
In addition, the closing of relay “1CR” contacts on line
56 also provides voltage to the
(line 53).

After
actuated contacts
necessary to load the compressor.

When either the first or second stage of the thermostat
calls for cooling the compressor starter auxiliary
contacts
the condenser fan motor

Contactors
through outdoor ambient thermostats
as the outdoor temperature changes. See table 7 on
page 8 for details on the action of the head pressure
control.

To insure that the indoor fan starter is energized,
before the condensing unit can be started, indoor fan
starter auxiliary contacts must be installed in the open
section of the control circuit between terminals Yl-Sl
and
identified on the schedmtic diagram as
5MA2.”

The unit control circuit incorporates a one time

down control. For example, when the second step on

(SWS1),

1CR

Y2-S2

overload contacts

(1

LP). With holding coil

“1MA”

contacts have closed the suction pressure

1MA or

on line 54 close. This starts compres-

“1CC”

2MA

on lines 70 and 72 will energize

“4M”

and

on lines 78 and 80. These contacts are

“1TC”

are calling for

1CR

contacts on line 56 will

“1M”

(1HP),

the system

(1OL

and the low

“1M”

ener-

“1CR”

contacts

1CR

contacts on line 59

“1OL”

overload module

on line 53 can open when

contactors 3M,

“5M”

can also be cycled

4M and 5M.

“1TA

and

“5MA1”

pump-

2TA”

and

the two-stage thermostat is satisfied and opens con­tacts 2TC on line 80, cooling relay 2CR is de-energized
opening relay contacts on lines 64 and 67. The circuit
on line 65 is maintained by the 2MA starter auxiliary
contacts on line 62. The liquid line solenoid valve on
line 67 is de-energized when the 2CR relay contacts
ahead of it are opened. De-energizing the solenoid
valve cuts off the flow of refrigerant to the number 2
expansion valve. The compressor continues to run be­cause the circuit to compressor starter holding coil 2M
is maintained by the 2MA auxiliary contacts on line 62.

The compressor continues to run and pump refrigerant
from the system until the setting of low pressure
cutout “2LP” on line 65 is reached and the contacts of
this control are opened. When this occurs the com­pressor starter holding coil 2M is de-energized, open­ing the starter contacts on lines 7, 9 and 11 and
auxiliary contacts 2MA on line 62. Suction pressure

switch “2LP” is automatic reset and when it does
reset, the compressor will not restart because both
relay contacts 2CR (Line 64) and starter auxiliary
contacts 2MA (Line
sor cannot be restarted until the 2TC thermostat again
calls for cooling and relay coil 2CR is energized again
closing 2CR contacts on lines 64 and 67. A similar
sequence will occur when thermostat contacts
open.

Also built into the compressor control circuit is a timed
off provision to prevent the compressor from restarting
after it has cycled off. A period of 3 to 5 minutes must
elapse before the compressor can restart. This function

is built into all model ST condensing units. On all units
except models ST010 and 020, this time delay is built
into the solid state control, on the ST010 and 020 it
is provided by separate time delay relays

“2TD.”

62)

are both open. The compres-

“1TD”

1TC

and

MAINTENANCE AND SERVICE

CRANKCASE HEATERS - The unit power supply
must be kept on at all times during the operating
season to keep the compressor crankcase heaters
energized. If the power is disconnected the com­pressor(s) could be damaged.

-

COMPRESSOR LUBRICATION
sealed compressors used in the model ST unit assem-

bly will not require additional lubrication once the
unit has been checked out and placed in operation.
In the event a large quantity of oil is lost as the
result of refrigerant leak, the system may require the

addition of oil.

CONDENSER FAN MOTORS
used on model ST008, 010, 013, 015 and 020 are
supplied with
ings. These motor bearings should be checked an­nually and lubricated with 20 weight non-detergent
oil.

The model ST025 and 030 units utilize permanently
lubricated ball bearing type motors.

CONDENSER COIL - The condenser coil should be
inspected and cleaned on a regular basis. Accumu­lation of leaves, paper and surface dirt should be
brushed from the finned surface. Annually the finned

prelubricated

sealed sleeve type bear-

The hermetically

-

The fan motors

surface should be cleaned using a fin cleaner. A dirty

condenser coil can increase unit power consumption
by as much as twenty percent.

INDOOR FAN AND EVAPORATOR COIL

indoor air handling system must be inspected and
serviced on a regular basis. Filters should be clean,

“V” belt tension adjusted and the evaporator coil

surface clean. In addition, the drain pan should be
clear of algea and the condensate should drain freely.

-

SEASONAL SHUTDOWN
need be made for end of season shutdown.

SEASONAL STARTUP

The crankcase heater circuit must be energized at
least eight hours before attempting to start the
compressor.

The air handling
serviced.

The unit condenser coil should be clean and free
of any debris that mav have accumulated during the
shutdown period.

Check and tighten all electrical connections.

Refer to section
Starting,” (page 6).

17

unit(s)

No special provisions

-

should be inspected and

“Preliminary Checks

-

The

before

TROUBLE SHOOTING GUIDE

Possible

Cause

FUSE

BLOWN

COMPRESSOR

STARTER

OVERLOAD

RELAY

TRIPPED

LOW

PRESSURE

CUTOUT
TRIPPED

T

HIGH

PRESSURE

CUTOUT
TRIPPED

Possible
Reasons

Motor or Winding

Grounded.

Fuse or Wire

Too Small

Compressor seized

Compressor

Drawing

Excessive

Current

Low Indoor

Refrigerant

Expansion Valve

not Opening

Refrigerant Charge

inoperative

Non-Condensables

in the Condenser

Overcharge

Refrigerant

Airflow

Restricted

Flow

Loss of

Evaporator

Fan

of

Checking

Procedure

Test for grounds, loose
wire connections, starter
contact adjustment

Check Table 9,

Megger motor

Check wiring for size
and/or loose connections

Check whether phase

unbalance exceeds 3%

Reset compressor lockout

Run compressor, check
starting, noises, and
for amperge drawn

Operate condensing unit,
check evaporator coil for
slow even frosting

Check liquid line strainer,

liquid line, suction line
for temperature change.
frost or ice will generally

indicate restriction.

Remove bulb, hold in

hand. Feel distributor
to see if valve opened

Check liquid line
temperature and
sight glass

Verify voltage at motor,

remove belt, spin

motor by hand.

Check air temperature

rise across condenser,

purge condenser,

observe effect on

condensing pressure

Purge refrigerant, check
for reduction in head
pressure

Page 10

Possible
Remedy

Replace wire, tighen con­nections of if
is grounded, replace it.

Replace as required

Replace compressor
if required

Replace wire if necessary,

tighten

Consult with

power company

Replace compressor

Clean or replace filters,

clean evaporator coil,
increase fan speed, correct
indoor fan rotation

Remove restriction

Adjust or replace
power element.

Leaktest system, repair
leak, evacuate when
necessary, recharge

Replace or repair motor

Evacuate system

Remove refrigerant until
operating pressures are

normal.

compressor

connections.

CONTROL

CIRCUIT

OPEN

MOTOR

TEMPERATURE

SENSOR OPEN

Air Cooled Condenser

Fan(s) Inoperative

Thermostat

Contacts

Open

Protective

Control

Defective
Defective

Starter

Coil

Motor

Temperature

too High

Verify voltage at motor,
check bearings.

Adjust to lowest setting,
check for voltage across
compressor starter
operating coil

Check switch operation

Check voltage at coil. If
burned will generally have
burned odor and dark
appearance

Check motor for failure,
check voltage, check

running current, check
refrigerant charge
Megger Motor

18

Replace motor or repair
defective bearing

If thermostat is defective,

replace

If defective, replace

If defective replace coil

Correct operating

conditions or if motor

is defective, replace.

TROUBLE SHOOTING GUIDE

NOISY

COM

PRESSOR

Low Refrigerant

Charge

Low

Air

Deliverv

Compressor

Not

Pumping

Compressor

Running

Unloaded

I

_iquid

refrigerani

flooding back

to compressor

Defective

Compressor

Head

Valves

System Leak

Coil and or Filter Dirty

Fan Speed too Low

Evaporator

Fan

Problem

Head Valves

Broken or

Head Gaskets

Blown

Unloading solenoid

Valve Stuck in

Unloaded Position

Faulty Expansion

Valve or Improper

Suoerheat Settinq

Liquid Refrigerant

Returning to Compressor

Expansion Valve and
Liquid Line Problems

Excess Oil in Svstem

Normal Wear

Check operating pressures Leak test, repair
and liquid line recharge
temperatures

Inspect filters and coil

Check fan speed and duct.Adjust fan speed, if

resistance against design

specifications

Start and stop fan,

observe rotation of

blades.

Check temperatures by

hand. Discharge and

suction lines warm cylinder Replace compressor

hot. Check suction and

discharge pressure

Check unloading solenoid Replace coil or valve

valve for defect

Check super heat

Try to pump system
down. Check how fast
discharge and suction
pressures equalize

Clean or replace filters,
clean coil

restriction is in duct may
require laraer motor

If fan rotation is wrong
correct by fan inter­changing motor
connections

Readjust or replace valve

If compressor will not

pump or pressures equalize
too fast, replace
compressor.

OIL

PRESSURE

PR0BLEMS -

Liquid

Refrigerant

Returning to

Compressor

Oil Trapping

Expansion Valve Not
Set Properly, Leaking
Liquid Solenoid Valve

Piping Problem

Check valves Adjust or replace

as necessary

Check piping arrangement

and size. Check for

Check for possible traps.

Modify as necessary

valve(s)

19