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