Hummer H1 Service Manual page 849

12-76 Electrical System
Step
7 Using a DVOM set to measure voltage, place the
positive lead on a battery power source. Place the
ground lead in cavity 6F(CKT440). Using the
scan tool, command the compressor clutch on.
Does meter display battery voltage?
8 Using a DVOM set to measure resistance. Check
resistance between cavity 4F(CKT348) and the
brown wire(CKT348)at the compressor clutch
connector. Is resistance below specification?
9 Ignition on, using a DVOM set to measure volt-
age, backprobe pin D5 in C28 at the
PCM(CKT440) with the negative lead. Place the
positive lead on a battery voltage source. Using
the scan tool, command the compressor clutch on.
Does the meter display battery voltage?
10 Ignition on, locate engine data list, and "A/C
Request". Turn mode dial on HVAC control head
to MAX A/C. Does scan tool display indicate A/C
request?
11 Ignition on, mode dial set to MAX A/C. Using a
DVOM set to measure voltage, backprobe the tan
wire(CKT198) at the temperature cutout switch
on the HVAC unit with the positive probe. Place
the negative lead on a known good ground. Is
voltage present?
12 Ignition on, mode dial set to MAX A/C. Using a
DVOM set to measure voltage, backprobe the yel-
low wire(CKT347) at the temperature cutout
switch on the HVAC unit with the positive probe.
Place the negative lead on a known good ground.
Is voltage present?
13 Using a DVOM set to measure voltage, ignition
on, mode dial set to MAX A/C, backprobe for
voltage on pin H (CKT347) in the 8 wire connec-
tor at the rear of the HVAC control head. Is volt-
age present?
4-1-00
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HVAC Compressor Inoperative (Continued)
Action Value(s) Yes
12v Go to step 8.
<.2 Ω
Replace com-
pressor relay.
12v Repair open, or
bad connection
in CKT440
between PCM
and A/C clutch
relay.
Replace PCM.
12v Go to step 14.
12v Replace the
temperature cut-
out switch.
12v Repair open,
bad connection
or short in
CKT347
between HVAC
control head and
temperature cut-
out switch.
®
No
Go to step 9.
Repair open or
bad connection
in CKT348
between clutch
relay and com-
pressor clutch.
Replace the
PCM.
Go to step 11.
Go to step 1.
Go to step 13.
Replace control
head.