System Diagnosis - Hummer H1 Service Manual

11-8 Heating/Ventilation/Air Conditioning (HVAC)

SYSTEM DIAGNOSIS

System diagnosis should begin with the system performance
checks described in this section. The checks will help verify
that a problem actually exists as opposed to an incorrect setting
by the vehicle operator.
In addition to the performance checks, problem verification
will also involve pressure testing, leak testing, individual com-
ponent testing, air flow and temperature testing, and refrigerant
recovery, evacuation, or recharge. The tools and equipment re-
quired for this purpose are described in each procedure.
Step
1 Actuate the water valve lever by hand, does it
move freely, and does spring pressure re-open the
valve when you release it.?
2 Loosen the clamp securing the water valve to the
body. Does the valve move freely now?
3 Using a hand vacuum pump J–35555, apply
18"Hg to the water valve vacuum motor. Does the
valve close and hold vacuum for at least 1 minute.
4 Release the vacuum on the water valve, does the
valve return to the open position?
5 Attach J–35555 to the vacuum supply line for the
water valve. Start and idle the engine. Rotate the
temperature control dial to the cold position. Is
sufficient vacuum present?
6 With J–35555 still attached to water valve vac-
uum supply line, rotate temperature control dial to
the hot position. Does atmosphere vent in?
7 Check for kinks, breaks and blockages in the vac-
uum harness between the water valve and the
HVAC control head. Are any found?
8 With J–35555 still attached to water valve vac-
uum supply line, disconnect HVAC control head 2
hose blk/wht connector. Does atmosphere vent
in?
9 Disconnect 2 hose blk/wht connector at HVAC
control head. Install J–35555 onto blk hose. Start
and Idle engine. Is sufficient vacuum present?
10 Locate vacuum connection on rear of vacuum
pump. Install J–35555 onto connection and start
and idle engine. Is sufficient vacuum present?
Water Valve Does Not Operate
Action
_______________________
The diagnosis charts outline common heater and A/C prob-
lems. The potential causes are listed in order of probability
(most-to-least probable). However, the charts are guides only
and will not outline all of the possible system faults that might
occur. System testing is still required for verification.
The primary diagnostic method of checking A/C system per-
formance is the pressure test. The test is performed with mani-
fold gauge set J–39183-C. The gauges
discharge pressures to be checked while the system is operat-
ing. The pressure test diagnosis charts describe common faults
that cause incorrect system pressures.
Value(s)
go to step 3
Problem is cor-
18"Hg go to step 4
go to step 5
18"Hg go to step 6
0" Hg System is working
Repair or replace
vacuum harness as
0"Hg Replace the con-
18"Hg Replace the con-
18"Hg Locate and repair
blockage/breakage
in vacuum harness
between vacuum
pump and HVAC
control head
allow suction and
Yes No
go to step 2
Replace the water
rected valve
Replace water
valve
Replace the water
valve
go to step7
go to step 8
correctly
go to step 9
necessary
Remove blockage
trol head in white vacuum
line to water
valve
go to step 10
trol head
Replace vacuum
pump
®