Hummer H2. Manual — part 1944

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Air Recirculation Malfunction

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Leak Testing in Heating, Ventilation and Air Conditioning

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Noise Diagnosis - Blower Motor in Heating, Ventilation and Air Conditioning

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Noise Diagnosis - Air Conditioning (A/C) System in Heating, Ventilation and Air Conditioning

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Noise Diagnosis - HVAC Module in Heating, Ventilation and Air Conditioning

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Odor Diagnosis in Heating, Ventilation and Air Conditioning

HVAC COMPRESSOR CLUTCH DOES NOT ENGAGE

Diagnostic Aids

A/C compressor clutch will not engage under the following conditions:

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The A/C high side line pressure is over 2957 kPa (429 psi).

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The A/C low side line pressure is under 138-172 kPa (20-25 psi).

To accurately determine what pressure the A/C low pressure switch opens and closes at, use Kent Moore GE-
47742 which will allow the technician to measure the switch point pressure at the switch.

Using a scan tool, monitor the "low pressure switch" status while monitoring the "low side" pressure at the
switch to determine the switch points of the low pressure switch.

The low pressure switch "connector seal" must be removed before plugging it into the switch for testing. The
"plunger effect" of plugging the connector with seal into the switch induces a pressure on the back side of the
switch, this pressure will skew the opening/closing characteristics of the switch 5-10 psi until the pressure
bleeds off. The time required for the connection induced pressure to bleed off can take 20 minutes or longer.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

2: The A/C compressor output is disabled if the engine is idling at a low unstable RPM.

3: The A/C compressor relay output is disabled if engine coolant temperature is above 121° C (250° F).
The engine coolant indicator will illuminate at this temperature.

4: This step ensures that the HVAC control module is receiving an input from the A/C switch.

5: These actions will enable the A/C compressor to operate.

6: This test ensures that there is sufficient refrigerant in the A/C system. The specific values come from
the A/C System Performance Test in Heating, Ventilation and Air Conditioning.

8: The A/C Low Pressure Switch parameter is out of range when the HVAC control module interprets the
signal being below 138-172 kPa (20-25 psi).

9: This action will simulate a closed switch condition. If the Pressure Cycle Switch parameter reads Low
Pressure than there is a circuit condition or a condition with the HVAC control module.

12: The A/C compressor relay output from the powertrain control module (PCM) is disabled if the A/C

2004 Hummer H2

2004 HVAC HVAC Systems - Automatic - Hummer H2

high side system pressure is interpreted to be higher than 2958 kPa (429 psi).

HVAC Compressor Clutch Does Not Engage

Step

Action

Values

Yes

No

Schematic Reference:HVAC Schematics
Connector End View Reference:HVAC Connector End Views
DEFINITION: The A/C compressor clutch will not engage when an A/C request has been made and a
Powertrain DTC has not been set.

1

Did you perform the HVAC Diagnostic
System Check?

-

Go to Step 2

Go to Diagnostic

System Check -

HVAC Systems -

Automatic

2

1. Start the engine.

2. Set the parking brake.

3. Place the vehicle in drive and

allow the engine to idle.

4. Observe the engine RPM.

Does the engine idle at a steady RPM?

-

Go to Step 3

Go to Rough,

Unstable, or

Incorrect Idle and

Stalling in Engine

Controls - 4.8L, 5.3L,

and 6.0L

3

1. Start the engine.

2. Observe the engine coolant

temperature indicator.

Is the engine coolant temperature
indicator illuminated?

-

Go to Diagnostic

System Check -

Engine Cooling in

Engine Cooling

Go to Step 4

4

1. Install a scan tool.

2. Turn ON the ignition, with the

engine OFF.

3. With a scan tool, observe the A/C

Switch parameter in the Heating
and Air Conditioning data list.

4. Activate the A/C request switch.

Does the scan tool indicate that the A/C
Switch parameter changes states?

-

Go to Step 5

Go to Step 26

5

1. Start the engine.

2. Place the blower motor switch in

the maximum speed position.

IMPORTANT:

For A/C compressor operation, the
ambient air temperature must be
above 5° C (40° F).

-

2004 Hummer H2

2004 HVAC HVAC Systems - Automatic - Hummer H2

3. Place the A/C request switch in

the ON position.

4. Place the left air temperature

switch in the coldest position.

Does the A/C compressor clutch
engage?

Go to Testing for

Intermittent

Conditions and Poor

Connections in Wiring

Systems

Go to Step 6

6

1. Park the vehicle inside or out of

direct sunlight.

2. Open the window in order to

ventilate the interior of the
vehicle.

3. Turn OFF the ignition.

4. If the A/C system was operating,

then wait for approximately 2
minutes.

5. Install J 43600 .

6. Record the ambient temperature at

the vehicle.

7. Record readings of the low and

high side STATIC pressures.

8. Compare the low and the high side

pressure values with the allowable
limits for the recorded ambient air
temperature.

Are the low and the high side pressure
values within the allowable limits for the
recorded ambient air temperature. Are
the pressure values within 103 kPa (15
psi) of each other?

Above

16° C

(60° F)

345 kPa

(50 psi)

Above

24° C

(75° F)

483 kPa

(70 psi)

Above

33° C

(90° F)

690 kPa

(100 psi)

Go to Step 7

Go to Leak Testing

in Heating,

Ventilation and Air

Conditioning

7

1. Start the engine.

2. With a scan tool, observe the A/C

Permission parameter in the
Heating and Air Conditioning data
list.

Does the A/C Permission parameter
display Granted?

-

Go to Step 14

Go to Step 8

1. Turn the ignition OFF.

2. Turn ON the ignition, with the

engine OFF.

2004 Hummer H2

2004 HVAC HVAC Systems - Automatic - Hummer H2

8

3. With a scan tool, observe the

Pressure Cycle Switch parameter
in the Heating and Air
Conditioning data list.

Does the Pressure Cycle Switch
parameter display Normal?

-

Go to Step 12

Go to Step 9

9

1. Turn OFF the ignition.

2. Disconnect the A/C low pressure

switch.

3. Turn ON the ignition, with the

engine OFF.

4. Connect a 3-ampere fused jumper

between the signal circuit and the
ground circuit of the A/C low
pressure switch.

5. Observe the Pressure Cycle

Switch parameter in the Heating
and Air Conditioning data list.

Does the Pressure Cycle Switch
parameter display Normal?

-

Go to Step 23

Go to Step 10

10

Test the signal circuit of the A/C low
pressure switch for a high resistance or
for an open. Refer to Circuit Testing
and to Wiring Repairs in Wiring
Systems.
Did you find and correct the condition?

-

Go to Step 35

Go to Step 11

11

Test the ground circuit of the A/C low
pressure switch for a high resistance or
for an open. Refer to Circuit Testing
and to Wiring Repairs in Wiring
Systems.
Did you find and correct the condition?

-

Go to Step 35

Go to Step 26

12

With a scan tool, observe the A/C
Pressure Sensor parameter in the
Powertrain Engine Data list.
Is the parameter less than the specified
value?

2958 kPa

(429 psi)

Go to Step 26

Go to Step 13

1. Turn OFF the ignition.

2. If the A/C system was operating,

then wait for approximately 2
minutes.

3. Install J 43600 .

2004 Hummer H2

2004 HVAC HVAC Systems - Automatic - Hummer H2