BENDIX TCH-008-005 User Manual

Technical Bulletin

Bulletin No.: PRO-08-05 Effective Date: 4/1/80 Cancels:PRO-08-05 dated 6/15/78 Page: 1 of 4

Subject: AD-2 AIR DRYER INSTALLATION RECOMMENDATIONS
The thousands of Bendix Air Dryers operating successfully in the field today attest to the

success of this unique filtration device.
A key factor in the successful operation and expected service life of the air dryer is

proper installation. Several factors are to be considered:
Operational Limitations
Because the air dryer is a regenerative type device, sufficient “purge” time must be

allowed. The dryer purge cycle is controlled by the governor and occurs when the
governor is in the “cut-out” position (compressor not compressing air).

The air dryer can be used on any vehicle where normal compressor loaded time is 90
seconds or less and unloaded is 30 seconds or more. On vehicles were the compressor
remains loaded for longer periods of time, increasing the purge volume may provide for
satisfactory operation; however, in such case it is recommended that a Bendix H.V.S.G.
representative or Bendix H.V.S.G. Engineering be contacted for recommendations
before proceeding with the installation.

Installation Recommendations

1. The dryer should be mounted securely outside the engine compartment in an area of
air flow when the vehicle is in motion. Do not mount close to heat producing
components such as exhaust stacks or the exhaust system.

2. The dryer must be mounted vertically with the purge valve exhaust towards the
ground. Connection from the governor unloader port to purge valve should be a
constantly declining line. Avoid routing the line over heat producing areas (exhaust
system, etc.).

3. The air dryer is installed in the compressor discharge line, not less than six feet from
a two cylinder compressor or ten feel from a single cylinder compressor when using
copper tubing. Teflon hose or wire braid hose can be substituted for copper tubing
using a 1½’ to 1’ ratio:

Examples: 1. Six feet of copper tubing can be replaced by nine feet of either

teflon or wire braid hose.

2. Six feet of copper tubing can be replaced by three feet of copper
tubing plus four and one-half feet of either teflon or wire braid
hose.

Maximum efficiency of the air dryer is dependent upon the discharge line cooling the
air before it reaches the air dryer; maximum air temperature at the dryer inlet should
not exceed 150ºF (66ºC).

4. The heating unit in the end cover prevents the purge valve from freezing. The
heater is thermostatically controlled with an operating range between 45ºF (7ºC)
and 85ºF (29ºC). Number 16 wire should be used, connecting to the “on” position
side of the engine control switch. Fuse with an 8 to 10 amp fuse on 12-volt systems
or a 4 to 5 amp fuse on 24 volt systems.

Desiccant Life
Compressor condition: The desiccant in the air dryer can handle the small amount of oil

passed by all compressors and provide satisfactory life; however, excessive amounts of
oil passed by the compressor will shorten desiccant life.

Proper application and installation: As discussed previously, proper application and
installation are extremely important in achieving satisfactory desiccant life.

Desiccant Replacement
The desiccant should be replaced when it is determined that the desiccant is sufficiently

contaminated to affect its ability to remove water and oil vapor. This test can be made
by checking for excessive contaminants in the first reservoir every three months; 25,000
miles or 900 operating hours. Small amounts of water caused by condensation will
occur in areas where more than 30ºF temperature variation occurs, however, the
presence of larger amounts of liquid may be an indication that the desiccant should be
changed.

It is generally recommended that the desiccant be replaced yearly; however, if
experience has shown that shortened or extended life has resulted in a particular
installation, the replacement interval should be reduced or increased accordingly.

To aid in proper maintenance of the air dryer and to assure proper installation, we have
developed the attached troubleshooting chart. This troubleshooting chart will eventually
be included in Service Data Sheet SD-08-2.