30
A-12
Symptom:
What it may indicate:
What you should do:
15.0 Compressor
constantly cycles
(compressor
remains unloaded
for a very short
time.)
(a) Air brake charging system
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
reduced by build-up of water, etc. Drain
and perform routine maintenance per Table
A, columns 3 & 4, on page A-3.
Go to Test 6 on page A-15.
Verify the operation of air dryer. Follow
vehicle OE maintenance recommendations
and component Service Data information.
Go to Test 2 on page A-14.
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
OE maintenance recommendations.
Go to Test 4 on page A-15.
Go to Test 2 on page A-14.
Go to Test 5 on page A-15.
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 the delivery lines to reservoir for
restrictions and repair as needed.
Verify the relief pressure is at the vehicle or
component manufacturer's specifications.
Replace if defective.
See Maintenance Schedule and Usage
Guidelines
(Table A, column 3, on page
A-3).
Verify operation of air dryer. Follow vehicle
OE maintenance recommendations and
component Service Data information.
Go to Test 5 on page A-15.
Go to Test 4 on page A-15.
13.0 Reservoir
safety valve
releases air
(a) Reservoir safety valve
malfunction.
(b) Governor malfunction.
(c) Compressor unloader mechanism
malfunction.
Verify the relief pressure is at vehicle or
component manufacturer's specifications
( t y p i c a l l y 1 5 0 p s i ) . R e p l a c e i f
defective.
Go to Test 4 on page A-15.
Go to Test 6 on page A-15.
Technician removes
governor.
Air dryer
safety valve
