22
Symptom: What it may indicate: What you should do:
15.0 Compressor
constantly cycles
(compressor
remains unloaded
for a very short
time.)
(a) A i r b r ak e c h a r gi n g s y s te m
maintenance not performed.
(b) Compressor unloader mechanism
malfunction.
(c) Air dryer purge valve or delivery
check valve malfunction.
(d) Air brake system leakage.
Available reservoir capacity may be re-
duced by build up of water etc. Drain and
perform routine maintenance per Table A,
columns 3 & 4, on page 13.
Go to Test 6 on page 25.
Verify operation of air dryer. Follow vehicle
O.E. maintenance recommendations and
component Service Data information.
Go to Test 2 on page 24.
14.0 Air dryer
doesn’t purge.
(Never hear
exhaust from air
dryer.)
(a) Air dryer malfunction.
(b) Governor malfunction.
(c) Air brake system leakage.
(d) Improper governor control line
installation to the reservoir.
Verify operation of air dryer. Follow vehicle
O.E. maintenance recommendations.
Go to Test 4 on page 25.
Go to Test 2 on page 24.
Go to Test 5 on page 25.
12.0 Air dryer
safety valve
releases air.
(a) Restriction between air dryer and
reservoir.
(b) Air dryer safety valve
malfunction.
(c) Air dryer maintenance not
performed.
(d) Air dryer malfunction.
(e) Improper governor control line
installation to the reservoir.
(f) Governor malfunction.
Inspect delivery lines to reservoir for restric-
tions and repair as needed.
Verify relief pressure is at vehicle or
component manufacturer specifications.
Replace if defective.
See Maintenance Schedule and Usage
Guidelines (Table A, column 3, on page
13).
Verify operation of air dryer. Follow vehicle
O.E. maintenance recommendations and
component Service Data information.
Go to Test 5 on page 25.
Go to Test 4 on page 25.
13.0 Reservoir
safety valve
releases air
(a) Reservoir safety valve
malfunction.
(b) Governor malfunction.
(c) Compressor unloader mechanism
malfunction.
Verify relief pressure is at vehicle or
component manufacturer's specifications
(typically 150 psi). Replace if defective.
Go to Test 4 on page 25.
Go to Test 6 on page 25.
Technician removes
governor.
Air dryer
safety valve
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