For 1990-2009 cars
Engine Controls Components
A/C System
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

### 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

Ensure no PCM DTC(s) are stored before using this table. The PCM will not activate the A/C clutch with a stored DTC.

### Test Description

The numbers below refer to numbers on the diagnostic table.

1. A/C DTCs will disable the A/C system. Repair A/C DTCs before proceeding.

2. The request circuit is shorted to a voltage if the scan tool displays A/C request as YES.

3. A condition exists with the request circuit between the PCM and the HVAC Controller or the HVAC Controller is malfunctioning if the test lamp did not illuminate.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 | Are any A/C DTCs set? | -- | Go to applicable DTC table. | Go to Step 3
3 |

1. Install the scan tool.
2. Idle the engine with the A/C OFF.
3. Monitor A/C request on the ENG 1 data list using a scan tool.

Does the scan tool indicate A/C request as YES?

--

Go to Step 8

Go to Step 4

4 | Turn ON the A/C. Does the scan tool indicate A/C request as YES? | -- | System OK | Go to Step 5
5 |

1. Turn OFF the ignition.
2. Disconnect the PCM connector C1 located on the opposite side of the manufacturer's logo. Refer to Powertrain Control Module Replacement/Programming .
3. Turn ON the ignition leaving the engine OFF.
4. Probe the A/C request circuit at the PCM electrical harness connector using the DMM J 39200 connected to ground. Refer to Probing Electrical Connectors in Wiring Systems.
5. Turn the A/C to the ON position,

Does the DMM display near the specified value when the A/C is enabled?

B+

Go to Step 10

Go to Step 6

6 |

1. Turn OFF the ignition.
2. Remove the HVAC Controller. Refer to Control Assembly Replacement in HVAC Manual.
3. Test the A/C request circuit for continuity between the HVAC Controller and the PCM using the DMM J 39200 . Refer to Testing for Continuity in Wiring Systems.

Does the DMM indicate continuity?

--

Go to Step 7

Go to Step 11

7 | Probe the A/C request circuit at the PCM harness connector using the test lamp J 35616-200 connected to B+. Does the test lamp illuminate? | -- | Go to Step 12 | Go to Step 9
8 | Inspect the A/C request circuit for a short to voltage. Repair the circuit as necessary if a short to voltage is found. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | System OK | Go to Step 9
9 | Important: Before replacing the HVAC Controller, refer to Functional Check in HVAC Manual. Replace the HVAC Controller. Refer to Control Assembly Replacement in HVAC Manual. Is the action complete? | -- | System OK | --
10 |

1. Inspect for poor connections at the PCM. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.
2. If you find a poor connection, repair as necessary. Refer to Repairing Connector Terminals in Wiring Systems.

Did you find and correct the condition?

--

System OK

Go to Step 13

11 | Repair the open A/C request circuit between the HVAC Controller and the PCM. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | --
12 | Repair the grounded A/C request circuit between the HVAC Controller and the PCM. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | --
13 | Important:: Program the replacement PCM. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Is the action complete? | -- | System OK | --