Diagnostic Aids
Compressor clutch engagement cannot be used to determine status of the low pressure switch. The low pressure switch is one of several inputs to the HVAC control module for A/C request authorization. A/C request is one of several inputs to the powertrain control module (PCM) that control A/C compressor clutch engagement.
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.
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The A/C compressor output is disabled if the engine is idling at a low unstable RPM.
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The A/C compressor relay output is disabled if the engine coolant temperature is above 121°C (250°F).
Step | Action | Value | Yes | No |
|---|---|---|---|---|
Schematic Reference: HVAC Schematics Connector End View Reference: HVAC Connector End Views DEFINITION: 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 review the HVAC operation and perform the necessary inspections? | -- | Go to Step 2 | |
Does the engine idle at a steady RPM? | -- | Go to Step 3 | Go to Rough, Unstable, or Incorrect Idle and Stalling for the 4.8L, 5.3L, and 6.0L engines or Rough, Unstable, or Incorrect Idle and Stalling for the 4.3L engine | |
Does the scan tool indicate that the ECT parameter is below 121°C (250°F)? | -- | Go to Step 4 | Go to Engine Overheating | |
4 |
Important: Ambient air temperature must be above 3°C (38°F).
Does the A/C compressor operate? | -- | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 5 |
5 |
Are the pressure values within the specifications for the ambient air temperature, and within 103 kPa (15 psi) of each other? | -- | Go to Step 6 | Go to Leak Testing |
Is the HVAC control assembly inoperative? | -- | Go to Step 8 | Go to Step 7 | |
7 |
Does the scan tool indicate that the A/C Request parameter is YES? | -- | Go to Step 10 | Go to Step 11 |
8 | Test the voltage supply circuits to the HVAC control assembly for a short to ground, a high resistance, or an open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 42 | Go to Step 9 |
9 | Test the ground circuit to the HVAC control assembly for an high resistance or an open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 42 | Go to Step 33 |
10 | Does the scan tool indicate the A/C Compressor Cycling Switch parameter is normal? | -- | Go to Step 17 | Go to Step 12 |
11 |
Does the scan tool indicate that the A/C Request parameter is YES? | -- | Go to Step 34 | Go to Step 13 |
12 |
Does the scan tool indicate the A/C Compressor Cycling Switch parameter is normal? | -- | Go to Step 31 | Go to Step 15 |
13 |
Did you find and correct the condition? | -- | Go to Step 42 | Go to Step 14 |
14 | Measure the voltage from the A/C request signal circuit at the powertrain control module (PCM). Does the voltage measure near the specified value? | B+ | Go to Step 35 | Go to Step 33 |
15 | Test the A/C low pressure switch signal circuit for a high resistance or an open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 42 | Go to Step 16 |
16 | Test the ground circuit of the A/C low pressure switch for a high resistance or an open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 42 | Go to Step 35 |
17 | 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 18 | Go to Step 20 |
18 |
Does the test lamp illuminate? | -- | Go to Step 19 | Go to Step 28 |
19 | Connect a 10-amp fused jumper wire between the switch side voltage circuit of the A/C compressor clutch relay and the A/C compressor clutch supply voltage circuit of the A/C compressor clutch. Does the A/C compressor clutch engage? | -- | Go to Step 30 | Go to Step 23 |
20 |
Does the test lamp illuminate? | -- | Go to Step 21 | Go to Step 27 |
21 |
Does the test lamp turn ON and OFF with each command? | -- | Go to Step 30 | Go to Step 22 |
22 | Does the test lamp remain illuminated with each command? | -- | Go to Step 25 | Go to Step 26 |
23 | Test the A/C compressor clutch supply voltage circuit for a short to ground, a high resistance, or an open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 42 | Go to Step 24 |
24 | Test the ground circuit of the A/C compressor clutch for a high resistance or an open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 42 | Go to Step 32 |
25 | 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 42 | Go to Step 35 |
26 | Test the control circuit of the A/C compressor clutch relay for an open or a short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 42 | Go to Step 35 |
27 | Repair the coil side voltage supply circuit of the A/C compressor clutch relay for an open or short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 42 | -- |
28 | Test the switch side voltage supply circuit of the A/C compressor clutch relay. Refer to Wiring Repairs . Did you complete the repair? | -- | Go to Step 42 | -- |
29 | Repair the compressor clutch supply voltage circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs . Did you complete the repair? | -- | Go to Step 42 | -- |
30 | Inspect for poor connections at the A/C compressor clutch relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 42 | Go to Step 36 |
31 | 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 . Did you find and correct the condition? | -- | Go to Step 42 | Go to Step 37 |
32 | 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 42 | Go to Step 39 |
33 | Inspect for poor connections at the harness connector of the HVAC control assembly. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 42 | Go to Step 40 |
34 | Inspect for poor connections at the harness connector of the A/C high pressure switch. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 42 | Go to Step 38 |
35 | Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 42 | Go to Step 41 |
36 | Replace the A/C compressor clutch relay. Refer to Compressor Relay Replacement . Did you complete the replacement? | -- | Go to Step 42 | -- |
37 | Replace the A/C low pressure switch. Refer to Air Conditioning Cycling Switch Replacement . Did you complete the replacement? | -- | Go to Step 42 | -- |
38 | Replace the A/C high pressure switch. Refer to Air Conditioning (A/C) High Pressure Switch Replacement . Did you complete the replacement? | -- | Go to Step 42 | -- |
39 | Replace the A/C compressor clutch coil. Refer to Air Conditioning Clutch Coil Replacement . Did you complete the replacement? | -- | Go to Step 42 | -- |
40 | Replace the HVAC control assembly. Refer to Heater and Air Conditioning Control Replacement . Did you complete the replacement? | -- | Go to Step 42 | -- |
41 |
Important: Perform the programming procedure for the PCM. Replace the PCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 42 | -- |
42 | Operate the system in order to verify the repair. Did you correct the condition? | -- | System OK | Go to Step 5 |
