Circuit Description:
The A/C clutch relay is PCM controlled to delay A/C clutch engagement after the A/C is turned ON. This allows the PCM to adjust engine RPM before the A/C clutch engages. The PCM will engage the A/C clutch any time A/C has been requested unless any of the following conditions exist:
| • | High coolant temperature. |
| • | Low A/C system pressure. |
| • | High A/C system pressure. |
| • | Wide open throttle. |
| • | High engine RPM. |
When the heater and A/C control is placed in the A/C mode, a 12 volt signal is sent to the PCM. When the PCM receives this signal the PCM will ground the A/C clutch relay control circuit to energize the A/C relay. This is shown on the scan tool as A/C request YES.
When a request for A/C has been detected by the PCM, the PCM will ground the A/C clutch relay control circuit, the relay contacts will close, and current will flow through the relay to the A/C compressor clutch.
When A/C request has been detected by the PCM, the cooling fan(s) will be turned ON when A/C pressure is above a predetermined pressure.
Diagnostic Aids
Before using this table, be sure no PCM DTC(s) are stored. The PCM will not activate the A/C clutch with a stored DTC.
Test Description
Number(s) below refer to number(s) on the diagnostic Table.
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A/C DTCs will disable the A/C system. Repair A/C DTCs before proceeding.
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If the scan tool displays A/C request as YES, indicates the request circuit is shorted to a voltage or the HVAC control assembly is faulty.
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This isolates the A/C Request Circuit and PCM from the HVAC control assembly.
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If the new fuses opens, determines the A/C request circuit is shorted to ground. If the A/C system operates properly after installing the new fuse, inspect circuit for an intermittent ground.
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Before replacing the HVAC control assembly, refer to Section 1B for further diagnoses.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||
2 | Are any A/C DTCs set? | -- | Go to the applicable DTC Table. | |
3 | Are the A/C fuses OK? | -- | ||
4 |
Does the scan tool indicate A/C request as YES? | -- | ||
5 | Engine idling with A/C ON. Does the scan tool indicate A/C request as YES? | -- | Go to Symptoms | |
6 |
Does the test light illuminate? | -- | ||
7 | Using a fused jumper wire, jumper terminals A and C together at the HVAC control assembly harness connector. Does the scan tool indicate A/C request as YES? | -- | ||
8 | Inspect the A/C request circuit for being open. If the circuit is open, repair as necessary. Was the condition found and corrected? | -- | System OK | |
9 | Disconnect the HVAC control assembly. Does the scan tool indicate A/C request as YES? | -- | ||
10 | Using a test light connected to ground, probe the A/C request circuit at the HVAC control assembly harness connector (PCM side). Does the test light illuminate? | -- | ||
11 | Repair the A/C request circuit for a short to voltage. Refer to Repair Procedures in Electrical Diagnosis (8A Cell 5). Is the action complete? | -- | System OK | -- |
12 | Replace the fuse and inspect circuit for a short to ground and repair as necessary. Is the action complete? | -- | System OK | -- |
13 | Repair the open ignition feed to the HVAC control assembly. Is the action complete? | -- | System OK | -- |
14 | Replace the HVAC control assembly. Is the action complete? | -- | System OK | -- |
15 | Check the PCM connections. If faulty connections are found, repair as necessary. Refer to Repair Procedures in Electrical Diagnosis (8A Cell 5). Was a problem found and corrected? | -- | System OK | |
16 |
Important: Replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming Replace the PCM. Is the action complete? | -- | System OK | -- |
