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Test Description

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

  1. 2:  The air conditioning (A/C) compressor relay output is disabled if the engine coolant temperature is above 128°C (262°F).
  2. 3:  Place the mode switch in any position except OFF and place the air temperature control switch in a cold setting. Use the bi-level mode for consistent testing of the A/C system operation.
  3. 6:  The HVAC control module is inoperative if the module does not respond to any operator control requests.
  4. 21:  The compressor is disabled when the evaporator temperature goes below 3°C (38°F).
  5. 29:  DTC B3933 A/C evaporator temperature sensor circuit may also set to diagnose this circuit.
  6. 31:  Check the connection by removing and securely reinstalling before replacement of the HVAC control is considered.
HVAC Compressor Clutch Does Not Engage

Step Action Yes No
Schematic Reference: HVAC Schematics 
Connector End View Reference: HVAC Connector End Views 
DEFINITION: The air conditioning (A/C) compressor clutch will not engage if an A/C request has been made and a powertrain DTC has not been set.
1 Did you perform the Diagnostic System Check - Vehicle? Go to Step 2  Go to Diagnostic System Check - Vehicle
2 
  1. Install a scan tool.
  2. Start the engine.
  3. Observe the Engine Coolant Temperature (ECT) parameter in the Engine Control Data, data list.
Does the scan tool indicate that the ECT parameter is above 128°C (262°F)?		 Go to Engine Overheating Go to Step 3 
3 
IMPORTANT: For A/C compressor operation, the evaporator air temperature must be above 3°C (38°F).
  1. Start the engine.
  2. Place the blower motor switch in the maximum speed position.
  3. Place the mode switch in the Vent position.
  4. Place the A/C request switch in the ON position.
  5. Place the air temperature switch in the coldest position.
Does the A/C compressor clutch operate?		 Go to Testing for Intermittent Conditions and Poor Connections Go to Step 4 
4
  1. Park the vehicle inside or out of direct sunlight.
  2. Open the window in order to ventilate the interior of the vehicle.
  3. If the A/C system was operating, then wait for approximately 2 minutes.
  4. Turn OFF the ignition.
  5. Install the J 43600  ACR 2000 Air Conditioning Service Center. See Special Tools .
  6. Record the ambient air 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. Refer to Air Conditioning (A/C) System Performance Test .
Are the low and high side pressure values within the allowable limits for the recorded ambient air temperature and within 103 kPa (15 psi) of each other?		 Go to Step 5  Go to Leak Testing
5
  1. Turn ON the ignition, with the engine OFF.
  2. With a scan tool, observe the A/C High Side Pressure Sensor parameter in the powertrain control module (PCM) or engine control module (ECM) data list.
  3. Compare the scan tool A/C High Side Pressure parameter to the high side pressure values on the J 43600  . See Special Tools .
Are the high side pressure values within 103 kPa (15 psi) of each other?		 Go to Step 6  Go to Step 22 
6  Is the HVAC control module inoperative? Go to Step 15  Go to Step 7 
7
  1. Start the engine.
  2. With a scan tool, observe the A/C Request Signal parameter in the PCM/ECM data list.
  3. Place the air temperature switch in the coldest position.
  4. Place the A/C request switch in the ON position.
Does the scan tool indicate that the A/C Request Signal parameter is Yes?		 Go to Step 9  Go to Step 8 
8
  1. Turn OFF the ignition.
  2. Test the A/C request signal circuit for the following conditions:
    • A short to voltage
    • A high resistance
    • An open
Refer to Circuit Testing and Wiring Repairs .Did you find and correct the condition?		 Go to Step 39  Go to Step 9 
9 With a scan tool, command the A/C compressor clutch relay ON and OFF.
Does the A/C compressor clutch relay turn ON and OFF with each command?		 Go to Step 13  Go to Step 10 
10
  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 coil side of the voltage supply circuit with a test lamp that is connected to a good ground.
Does the test lamp illuminate?		 Go to Step 11  Go to Step 25 
11
  1. Connect a test lamp between the control circuit and the coil side of the voltage supply circuit.
  2. With a scan tool, command the A/C compressor clutch relay ON and OFF in scan tool special functions.
Does the test lamp turn ON and OFF with each command?		 Go to Step 27  Go to Step 12 
12 Does the test lamp remain illuminated with each command? Go to Step 19  Go to Step 17 
13
  1. Turn OFF the ignition.
  2. Disconnect the A/C compressor clutch relay.
  3. Probe the switch side of the voltage supply circuit with a test lamp that is connected to a good ground.
Does the test lamp illuminate?		 Go to Step 14  Go to Step 24 
14
  1. Connect a 10-amp fused jumper between the switch side voltage circuit of the clutch relay and the supply voltage circuit of the clutch.
  2. Turn ON the ignition, with the engine OFF.
Does the A/C compressor clutch engage?		 Go to Step 27  Go to Step 20 
15 Test the ignition 1 voltage circuit of the HVAC control module for the following conditions:
  • A short to voltage
  • A high resistance
  • An open

Refer to Circuit Testing and Wiring Repairs .
Did you find and correct the condition?		 Go to Step 39  Go to Step 16 
16 Test the ground circuit of the HVAC control module for an open. Refer to Circuit Testing and Wiring Repairs .
Did you find and correct the condition?		 Go to Step 39  Go to Step 31 
17 Test the control circuit of the A/C compressor clutch relay for an open. Refer to Circuit Testing and Wiring Repairs .
Did you find and correct the condition?		 Go to Step 39  Go to Step 32 
18 Test the A/C request signal circuit for the following conditions:
  • A short to voltage
  • A high resistance
  • An open

Refer to Circuit Testing and Wiring Repairs .
Did you find and correct the condition?		 Go to Step 39  Go to Step 21 
19 Test the control circuit of the A/C compressor clutch relay for a short to ground. Refer to Circuit Testing and Wiring Repairs .
Did you find and correct the condition?		 Go to Step 39  Go to Step 32 
20 Test the supply voltage circuit at the A/C compressor clutch relay for the following conditions:
  • A short to voltage
  • A high resistance
  • An open

Refer to Circuit Testing and Wiring Repairs .
Did you find and correct the condition?		 Go to Step 39  Go to Step 23 
21 
  1. With a scan tool, check the Evaporator Temperature Sensor data in the HVAC scan tool data list.
  2. Disconnect the Evaporator Temperature Sensor.
  3. Measure the evaporator sensor resistance.
Is the resistance measured within the minimum/maximum resistance range for the temperature value indicated?		 Go to Step 22  Go to Step 29 
22 Test the ground circuit of the A/C refrigerant pressure sensor for a high resistance or for an open. Refer to Circuit Testing and Wiring Repairs .
Did you find and correct the condition?		 Go to Step 39  Go to Step 26 
23 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 .
Did you find and correct the condition?		 Go to Step 39  Go to Step 28 
24 Repair the switch side voltage supply circuit of the relay. Refer to Wiring Repairs .
Did you complete the repair?		 Go to Step 39  -
25 Repair the coil side of the voltage supply circuit of the relay. Refer to Wiring Repairs .
Did you complete the repair?		 Go to Step 39  -
26 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 .
Did you find and correct the condition?		 Go to Step 39  Go to Step 33 
27 Inspect for poor connections at the relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .
Did you find and correct the condition?		 Go to Step 39  Go to Step 35 
28 Inspect for poor connections at the harness connector of the A/C compressor clutch. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .
Did you find and correct the condition?		 Go to Step 39  Go to Step 36 
29  Test the evaporator temperature sensor circuits for the following conditions:
  • A short to voltage
  • A high resistance
  • An open

Refer to Circuit Testing and Wiring Repairs .
Did you find and correct the condition?		 Go to Step 39  Go to Step 30 
30 Inspect for poor connections at the harness connector of the evaporator temperature sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .
Did you find and correct the condition?		 Go to Step 39  Go to Step 34 
31  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 .
Did you find and correct the condition?		 Go to Step 39  Go to Step 37 
32 Inspect for poor connections at the harness connector of the PCM/ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .
Did you find and correct the condition?		 Go to Step 39  Go to Step 38 
33 Replace the A/C refrigerant pressure sensor. Refer to Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement .
Did you complete the replacement?		 Go to Step 39  -
34 Replace the evaporator temperature sensor. Refer to Evaporator Temperature Sensor Replacement .
Did you complete the replacement?		 Go to Step 39  -
35 Replace the relay.
Did you complete the replacement?		 Go to Step 39  -
36 Replace the A/C compressor. Refer to Compressor Replacement .
Did you complete the replacement?		 Go to Step 39  -
37 Replace the HVAC control module. Refer to Control Module References for replacement, setup and programming.
Did you complete the replacement?		 Go to Step 39  -
38 Replace the PCM/ECM. Refer to Control Module References for replacement, setup and programming.
Did you complete the replacement?		 Go to Step 39  -
39 Operate the system in order to verify the repair.
Did you correct the condition?		 System OK Go to Step 4 
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