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Test Description

WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

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

  1. 2:  The A/C compressor output is disabled if the engine is idling at a low unstable RPM.
  2. 3:  The A/C compressor relay output is disabled if ECT is above 121°C (250°F). The Engine Coolant indicator will illuminate at this temperature.
  3. 4:  This step ensures that the HVAC control module is receiving an input from the A/C switch.
  4. 5:  These actions will enable the A/C compressor to operate.
  5. 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.
  6. 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).
  7. 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.
  8. 12:  The A/C compressor relay output from the PCM is disabled if the A/C high side system pressure is interpreted to be higher than 2 958 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 Diagnostic System Check - HVAC Systems - Manual? - Go to Step 2  Go to Diagnostic System Check - HVAC Systems - Manual 
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, Rough, Unstable, or Incorrect Idle and Stalling in Engine Controls - 4.3L, Rough, Unstable, or Incorrect Idle and Stalling in Engine Controls - 6.6L (LB7), or Rough, Unstable, or Incorrect Idle and Stalling in Engine Controls - 8.1L
3 
  1. Start the engine.
  2. Observe the Coolant Temperature indicator.
Is the engine coolant temperature (ECT) 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 
IMPORTANT: For A/C compressor operation, the ambient air temperature (AAT) must be above 5°C (40°F).
  1. Start the engine.
  2. Place the blower motor switch in the maximum speed position.
  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 the J 43600  ACR 2000 Air Conditioning Service Center.
  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 AAT.
Are the low and the high side pressure values within the allowable limits for the recorded AAT? 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 
8 
  1. Turn the ignition OFF.
  2. Turn ON the ignition, with the engine OFF.
  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-amp 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 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 Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 35  Go to Step 23 
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?		 2 958 kPa (429 psi) Go to Step 26  Go to Step 13 
13
  1. Turn OFF the ignition.
  2. If the A/C system was operating, then wait for approximately 2 minutes.
  3. Install J 43600  .
  4. Turn ON the ignition, with the engine OFF.
  5. With a scan tool, observe the A/C Pressure Sensor parameter.
  6. Compare the A/C Pressure Sensor parameter on the scan tool to the A/C high side pressure on J 43600  .
Are the high side pressure values within 103 kPa (15 psi) of each other?		 - Go to Air Conditioning (A/C) System Performance Test (without PHT)Air Conditioning (A/C) System Performance Test (with PHT) in Heating, Ventilation and Air Conditioning Go to Step 24 
14
  1. Start the engine.
  2. With a scan tool, command the A/C Permission to Granted and Withheld.
Does the relay turn ON and OFF with each command?		 - Go to Step 15  Go to Step 19 
15
  1. Turn OFF the ignition.
  2. Test the battery positive voltage circuit of the A/C compressor clutch relay for a high resistance or for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 35  Go to Step 16 
16
  1. Turn OFF the ignition.
  2. Connect a 10-amp fused jumper between the battery positive circuit of the A/C compressor relay and the A/C compressor supply voltage circuit.
  3. Disconnect the A/C compressor connector.
  4. Turn ON the ignition, with engine OFF.
  5. Connect a test lamp between the A/C compressor supply voltage circuit and the ground circuit of the A/C compressor.
Does the test light illuminate?		 - Go to Step 25  Go to Step 17 
17 Test the supply voltage circuit of the A/C compressor clutch for a high resistance or for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 35  Go to Step 18 
18 Test the ground circuit of the A/C compressor clutch for a high resistance or for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 35  Go to Step 22 
19
  1. Turn OFF the ignition.
  2. Disconnect the A/C compressor clutch relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the ignition 3 voltage circuit of the A/C compressor clutch relay with a test lamp that is connected to ground.
Does the test lamp illuminate?		 - Go to Step 20  Go to Step 28 
20
  1. Start the engine.
  2. Connect a test lamp between the control circuit and the ignition 3 voltage circuit of the A/C compressor clutch relay.
  3. With a scan tool, command the A/C Permission to Granted.
Does the test lamp illuminate?		 - Go to Step 22  Go to Step 21 
21
  1. Turn OFF the ignition.
  2. Test the A/C compressor clutch control circuit of the A/C compressor clutch relay for a high resistance or for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 35  Go to Step 27 
22
  1. Turn OFF the ignition.
  2. Inspect for poor connections at the A/C compressor clutch relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 35  Go to Step 29 
23 Inspect for poor connections at the harness connector of the A/C low pressure switch. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 35  Go to Step 30 
24 Inspect for poor connections at the harness connector of the A/C refrigerant pressure sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 35  Go to Step 31 
25 Inspect for poor connections at the harness connector of the A/C compressor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 35  Go to Step 32 
26 Inspect for poor connections at the harness connector of the HVAC control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 35  Go to Step 33 
27 Inspect for poor connections at the harness connector of the powertrain control module (PCM) or engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 35  Go to Step 34 
28 Repair the ignition 3 voltage circuit of the A/C compressor clutch relay. Refer to Wiring Repairs in Wiring Systems.
Did you complete the repair?		 - Go to Step 35  -
29 Replace the A/C compressor clutch relay.
Did you complete the replacement?		 - Go to Step 35  -
30 Replace the A/C low pressure switch. Refer to Air Conditioning (A/C) Low Pressure Switch Replacement in Heating, Ventilation and Air Conditioning.
Did you complete the replacement?		 - Go to Step 35  -
31 Replace the A/C refrigerant pressure sensor. Refer to Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement in Heating, Ventilation and Air Conditioning.
Did you complete the replacement?		 - Go to Step 35  -
32 Replace the A/C compressor clutch. Refer to Compressor Clutch Plate/Hub Assembly Replacement in Heating, Ventilation and Air Conditioning.
Did you complete the replacement?		 - Go to Step 35  -
33 Replace the HVAC control module. Refer to HVAC Control Module Replacement .
Did you complete the replacement?		 - Go to Step 35  -
34
IMPORTANT: Program the PCM/ECM.
Replace the PCM/ECM. Refer to the appropriate procedure:Did you complete the replacement?		 - Go to Step 35  -
35 Operate the system in order to verify the repair.
Did you correct the condition?		 - System OK Go to Step 5 
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