Bendix Commercial Vehicle Systems AD-2 AIR DRYERS 7/04 - Manual (Page 15)

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AD-2 ™ AIR DRYER TROUBLESHOOTING CHART
SYMPTOM CAUSE REMEDY
1. Dryer is constantly A. Excessive system leakage. A. Test for excessive leakage and repair.
“cycling” or purging. Allowable leakage:
Pre-121 vehicles, single vehicle - 2 psi/minute.
Tractor trailer - 3 psi/minute.
121 vehicles, single vehicle - 1 psi/minute per
service reservoir.
Tractor trailer - 3 psi/minute per service
reservoir.
B. Excessive leakage in fittings, hoses B. Using soap solution, test for leakage at fittings,
and tubing connected to compressor, drain valve (if any) and safety valve in first
air dryer and first reservoir. reservoir. Repair or replace as necessary.
C. Defective check valve between air dryer C. Test check valve. Leakage should not exceed
and first reservoir. (In standard AD-2 ™ 1" soap bubble in five seconds. It may be
air dryer, check valve to outlet port.) necessary to remove check valve to test.
Repair or replace as necessary.
D. Defective governor. D. Test governor for proper cut-in or cut-out
pressures and excessive leakage in both
positions.
E. Leaking purge valve in air dryer end E. Remove end cover. Apply 120 psi at control
cover (control side). port. Soap both sides around purge valve to test
for control piston leakage.
(Permissible leakage - 1" bubble in 5 seconds.)+`
F. Compressor unloader mechanism F. Remove air strainer or fitting from compressor
leaking excessively. inlet cavity. With compressor unloaded, check
for unloader piston leakage.
Slight leakage permissible.
2. Water in vehicle A. Desiccant requires replacement. A. Replace desiccant cartridge.
reservoirs.
B. Improper discharge line length or B. Minimum of six-foot metal tubing for
improper line material. two-cylinder compressor; ten-foot for
one-cylinder compressor. Flex hose
can be substituted at ratio of 1-1/2' flex hose for
each 1' of metal.
C. Air system charged from outside air C. If system must have outside air fill provision,
source (outside air not passing outside air should pass through air dryer.
through air dryer). (Unused inlet on air dryer can be used.) Use of
this should be minimized.
D. Air dryer not purging (see Symptom D. See cause and remedy for Symptom #5.)
#5).
E. Purge (air exhaust) time insufficient E. Check causes and remedies for Symptom #1.
due to excessive system leakage
(see causes for Symptom #1).
F. Air dryer/vehicle application requires F. When compressor is loaded (compressing)
additional purge volume. longer than 90 seconds during normal
operation, additional purge volume may be
needed. (Before proceeding, contact Bendix
representation for consultation.)
G. Air dryer not compatible with vehicle G. Air dryer requires minimum purge time of 30
air system requirement - (Improper air seconds. If compressor stays loaded longer
dryer/vehicle application). than 90 seconds and additional purge volume is
added, longer purge time is required. Air dryer
efficiency will decrease as compressor
loaded time increases beyond 120 seconds,
during normal operation of the vehicle. (This
limitation assumes a compressor of
approximately 12 CFM and engine operation at
1600-1900 RPM.) The air dryer will
accommodate occasional longer loaded times,
such as initial system build-up.
3. Safety valve on air dryer A. Desiccant cartridge plugged or A. Check compressor for excessive oil passing
“popping off” or saturated. and/or correct compressor installation. Repair
exhausting air. or replace as necessary.
Rebuild or replace cartridge.
B. Defective check valve between air B. Test to determine if air is passing through
dryer outlet port and first reservoir. (in check valve. Repair or replace.
standard AD-2 ™ air dryer, check valve
in outlet port.)
C. Defective fittings, hose or tubing C. Check to determine if air is reaching first
between air dryer and first reservoir. reservoir. Inspect for kinked tubing or hose.
Check for undrilled or restricted hose or tubing
fittings.