Electrical; System Performance Checks - Hummer H1 Service Manual

11-2 Heating/Ventilation/Air Conditioning (HVAC)

SYSTEM PERFORMANCE CHECKS

Before performing any air conditioning repair, perform the fol-
lowing:
1. Check drivebelt for wear, damage, or loss of tension.
Replace drivebelt as necessary.
1. Check compressor for secure mounting and proper
alignment. Tighten loose hardware and align as necessary.
2. Visually inspect compressor, hoses and other accessible
parts of system for damage or leaks. Look for patches of
dirt, dust, and oil build-up. Refrigerant leaks usually
involve compressor oil loss. This is especially applicable
to clutch end of compressor.
3. Verify operation of climate control system by performing
following:
a. With the mode (air flow) control knob set to OFF, run
engine to operating temperature (180°-240°F (82°-
116°C)).
b. Rotate temperature control knob clockwise until it
stops at the warmest setting.
c. Rotate mode control knob counterclockwise until it
stops at the face setting.
d. Turn fan control knob to any setting above LO and
note direction and temperature of air flow.
e. Verify that heated air is coming from instrument
panel vents.
f. Rotate mode control knob clockwise to the next
setting, floor vents, and verify that heated air comes
from appropriate vents.
g. Continue checking the air flow positions, floor/defrost
blend, and defrost.
NOTE: Any time the air flow control knob is placed in defrost
or a defrost blend position (with an ambient temperature above
40°F), the compressor clutch engages to dehumidify the in-
coming air.
h. Rotate the temperature control knob counterclockwise
to its coldest extreme. Verify that cold air comes from
the defrost vents. If the outside air temperature is
40°F or warmer, the refrigeration system will be
responsible for cooling the air. If it is cooler than
40°F, the compressor will not cycle and the incoming
air will simply be the outside air directed into the
passenger compartment.
i. Rotate the mode control knob counterclockwise until
it stops at the Max A/C panel setting and verify that
compressor clutch engages and air becomes colder.
Turn the mode dial to the A/C setting. Verify that the
air recirculation door closes, and the system brings in
outside air.
j. Check that blower motor delivers air at four different
speeds. If not, perform electrical troubleshooting.
Repair or replace blower motor, switch, relay, or
blower motor resistor block.
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k. Check water control valve operation. Heater Shutoff
Valve should open completely when temperature
control knob is rotated clockwise.
Heating System Tests
In most cases, a low heat condition means an insufficient quan-
tity of heated engine coolant is flowing through the heater core.
Check as follows:
1. Check engine coolant level. If level is low, add coolant and
inspect for leaks. If coolant level is correct, continue with
tests.
2. Check pressure cap on surge tank for improper sealing
with tester J–24460-01 or equivalent. If cap is OK,
continue with tests. Replace cap if it fails to seal and
recheck heater operation.
3. Set heater controls to highest heat setting.
4. Operate engine until coolant is at normal operating
temperature (180-220° F or 82-113° C).
5. Check temperature of coolant flowing through heater core
inlet and outlet hoses.
• If both hoses feel hot and are about the same tempera-
ture, water control valve is OK and core is not restricted.
Continue with test.
• If both hoses are only warm (or even cool), engine is ei-
ther not at operating temperature, or a water pump or
thermostat problem has occurred.
• If inlet hose is cool, or only slightly warm, water control
valve or vacuum solenoid problem has occurred. Test as
described in this section.
6. If heat output is still unsatisfactory but all else checks
correctly, problem is with heat door in main unit, or in
outlet ducts.
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