GM Service Manual Online
For 1990-2009 cars only

Object Number: 101348  Size: LF
OBD II Symbol Description Notice
Engine Controls Components
Cell 20: A/C Compressor Controls
Handling ESD Sensitive Parts Notice

Circuit Description:

This diagnostic is only for the C60 A/C system (manual control). For further diagnosis of the CJ2 system, refer to HVAC.

The A/C clutch relay is PCM controlled in order to delay the A/C clutch engagement after the system turns on the A/C. This allows the PCM to adjust the engine RPM before the A/C clutch engages. The PCM engages the A/C clutch any time the system requests the A/C 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, the system sends a 12 volt signal to the PCM. When the PCM receives this signal the PCM grounds the A/C clutch relay control circuit in order to energize the A/C relay. The scan tool shows this as A/C request YES.

When the PCM has detected a request for the A/C, the PCM grounds the A/C clutch relay control circuit, the relay contacts close, and current flows through the relay to the A/C compressor clutch.

When the PCM has detected a request for the A/C, the PCM turns on the cooling fan(s) when the 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

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 problem exists with the request circuit between the PCM and the HVAC Programmer or the HVAC Programmer is malfunctioning if the test lamp did not illuminate. Refer to Body and Accessories/Wiring Systems or HVAC for further diagnosis.

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 ignition with the A/C ON.

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 located on the opposite side of the manufacturer's logo. Refer to Powertrain Control Module/Throttle Actuator Control Module Replacement .
  3. Turn ON the ignition leaving the engine OFF.
  4. Probe the A/C request circuit at the PCM electrical harness connector using a DMM J 39200 connected to ground.
  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. Disconnect the HVAC Programmer.
  3. Check the A/C request circuit for continuity between the HVAC Programmer and the PCM using a DMM J 39200 .

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 a 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 Body and Accessories/Wiring Systems.

Did you find a problem and correct it?

--

System OK

Go to Step 9

9

Important: Before replacing the HVAC Programmer, refer to HVAC for further diagnosis.

Replace the HVAC Programmer.

Is the action complete?

--

System OK

--

10

Check the PCM connections. Repair faulty connections as necessary. Refer to Body and Accessories/Wiring Systems.

Did you find a problem and correct it?

--

System OK

Go to Step 13

11

Repair the open A/C request circuit between the HVAC Programmer and the PCM. Refer to Body and Accessories/Wiring Systems.

Is the action complete?

--

System OK

--

12

Repair the grounded A/C request circuit between the HVAC Programmer and the PCM. Refer to Body and Accessories/Wiring Systems.

Is the action complete?

--

System OK

--

13

Important:: Program the replacement PCM. Refer to Powertrain Control Module/Throttle Actuator Control Module Replacement .

Replace the PCM.

Is the action complete?

--

System OK

--