Powertrain Control Module Controlled Air Conditioning (A/C) Circuit Diagnosis. Cadillac Concours 1996

For 1990-2009 cars

### A/C System

A/C operation is requested by the ACM using a serial data (Class 2) message to the PCM. The PCM will ground the A/C relay allowing current to flow through the A/C Compressor clutch coil. The PCM will disable or inhibit A/C compressor clutch operation during the following conditions:

• | High power steering load indicated

• | Engine not running

• | Engine at wide open throttle

• | Outside temperature below approximately 4°C (40°F)

• | Certain PCM DTCs set

The PCM will also engage the A/C compressor clutch during cranking in colder weather to prevent A/C slugging.

### Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

1. Since many DTCs disable A/C clutch operation, any DTCs must be repaired and cleared before using this table.

2. An A/C Relay status of OFF indicates that the PCM is not allowing A/C clutch operation (DTCs set or low outside temp. etc.) or the ACM is not requesting A/C operation from the PCM. Check for HVAC DTC's which may inhibit the ACM from requesting A/C clutch operation.

   To verify PCM control of the A/C clutch, use the output test for the A/C relay and command the A/C clutch ON and OFF with the engine Running . Watch for the A/C clutch to engage and disengage.

3. Refer to the HVAC section for diagnosis of intermittent operation. Check for proper system pressures and for HVAC DTC's that may be stored indicating a previous fault condition.

4. A lighted test light indicates the PCM can control the A/C relay ON. No A/C clutch operation could be caused by a blown fuse, a defective relay, A/C system pressure faults which open one of the A/C pressure switches or a defective A/C compressor clutch coil or ground. Refer to the HVAC section for diagnosis of these components.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to Powertrain OBD System Check

2

1. Start and idle the engine.
2. Select MAX cold - Auto.
3. Observe the scan tool status for A/C Relay.

Does the display indicate the A/C relay is requested ON?

--

Go to Step 3

A/C operation inhibited. Refer to Test Descriptions

3 | Observe the operation of the A/C clutch. Is the A/C clutch engaged? | -- | Go to Step 4 | Go to Step 5

4

1. Turn the A/C controls to OFF.
2. With the scan tool status for the A/C Relay indicating OFF, observe the operation of the compressor clutch.

Does the compressor clutch operate while requested OFF?

--

Go to Step 9

PCM control OK. Refer to Test Descriptions

5

1. Remove the A/C Compressor Clutch relay.
2. Using a test light connected to BATTERY VOLTAGE, probe the A/C Compressor Clutch relay terminal D1 with the engine running and A/C requested ON.

Is the test light illuminated?

--

PCM control OK. Refer to Test Descriptions

Go to Step 6

6 | Using a test light connected to a good GROUND, probe the A/C Compressor Clutch relay terminal D1. Is the test light illuminated? | -- | Go to Step 10 | Go to Step 7

7

1. Turn the engine OFF.
2. Disconnect PCM connector C1.
3. Using the DMM J 39200, measure the resistance between PCM connector C1 terminal 25 and the A/C Compressor Clutch Control relay terminal D1.

Is the resistance the same or less than the value specified?

5 ohms

Go to Step 11

Go to Step 8

8 | Repair the open in the A/C Compressor Clutch Control circuit. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --

9

Check for the following conditions and repair as necessary:

• | A shorted to ground A/C Relay Control circuit.

• | An A/C clutch relay with stuck closed switch contacts.

• | A short to voltage in circuit 59 to the A/C compressor clutch.

Was any of the above conditions located and repaired?

--

Go to Powertrain Control Module Diagnosis for Verify Repair

Go to Step 11

10 | Repair the short to voltage on the A/C compressor clutch relay control circuit. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --

11

1. Check terminal contact at PCM connector C1 terminal 25 and at the A/C Compressor Control Relay terminal D1.
2. Repair terminal contact if needed.

Was a repair made to the terminal contact at either connector?

--

Go to Powertrain Control Module Diagnosis for Verify Repair

Go to Step 12

12 | Replace the PCM. Refer to PCM Replacement/Programming . Is the replacement complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --