TM 5-3805-262-20
3-24. ACCESSORIES TROUBLESHOOTING (CONT)
MALFUNCTION
TEST OR INSPECTION
CORRECTIVE ACTION
8. DEFROSTER MOTOR DOES NOT OPERATE (Cont).
Step 4.
Step 5.
Step 6.
Disconnect battery ground cable (page 5-148).
Disconnect wire connected between cab relay BAT. terminal and cab 30
ampere circuit breaker long, silver terminal.
Reconnect battery ground cable.
Connect multimeter between long, silver terminal of cab 30 ampere
c i r c u i t b r e a k e r a n d c h a s s i s .
Multimeter shall indicate 24 volts.
a. If multimeter indicates zero, replace cab 30 ampere circuit
breaker (page 5-26).
b. If multimeter indicates 24 volts, a short circuit to ground
e x i s t s i n c a b e l e c t r i c a l c i r c u i t . I s o l a t e d e f e c t i v e c i r c u i t by
r e c o n n e c t i n g w i r e f r o m c a b r e l a y B A T . t e r m i n a l t o l o n g , s i l v er
terminal of cab circuit breaker. Then , at cab switch panel, dis-
connect and tape wires connected to each of the three circuit
breakers one at a time and check if remaining circuit(s) operate
when associated switch is operated. If circuit is okay, problem
is in circuit associated with breaker from which wire was dis-
connected.
Press 6 ampere circuit breaker on cab switch panel.
Check if defroster motor operates.
a. If defroster motor operates, problem was momentary short in
c i r c u i t .
b . I f c i r c u i t b r e a k e r b l o w s , a short to ground exists in circuit.
Go to step 6 below.
c. If defroster motor does not
operate, go to step 7 below.
Turn ignition key switch to off
p o s i t i o n.
Remove HEAT CONTROL knob from
cab switch panel by pulling
s t r a i g h t u p o f f c o n t r o l s h a f t.
Remove four screws securing cab
switch panel.
3-171
