Air Conditioning (A/C) Request Circuit Check. Buick Roadmaster 1996

For 1990-2009 cars

### 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. For the system schematic, refer to

#### A/C Controls - C60

Engine Controls Components
Powertrain Control Module (PCM)
A/C Controls - C67 and C68
Transmission Controls
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
or

#### A/C Controls - C67 and C68

Engine Controls Components
Powertrain Control Module (PCM)
Engine Cooling Fan Control - w/o VO8
A/C Controls - C60
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
.

### 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.

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

2. If the scan tool displays A/C request as YES, indicates the request circuit is shorted to a voltage.

3. If the test light did not illuminate, indicates a problem with the request circuit between the A/C pressure switch and the control head or the control head is malfunctioning. Refer to Repair Procedures in Electrical Diagnosis (8A Cell 67).

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | 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. Engine idling with A/C OFF.
3. Using a scan tool on the ENG 1 data list, monitor A/C request.

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

--

Go to Step 9

Go to Step 4

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

5

1. Disconnect the A/C pressure cycling switch.
2. Using a DVM J 39200, probe the A/C request circuit (HVAC side of the of the A/C pressure cycling switch electrical connector.)

Does the DVM display near the specified voltage?

B+

Go to Step 6

Go to Repair Procedures in Electrical Diagnosis (8A Cell 67).

6 | Using a fused jumper wire, jumper terminals A and B together at the A/C pressure cycling switch harness connector. Does the scan tool indicate A/C request as YES? | -- | Go to Step 13 | Go to Step 7

7

1. Turn the ignition OFF.
2. Disconnect the PCM connector C2.
3. Check the continuity of A/C request circuit between the PCM and the A/C pressure cycling switch.

Is the A/C request circuit open?

--

Go to Step 15

Go to Step 8

8 | Is the A/C request circuit shorted to ground? | -- | Go to Step 16 | Go to Step 12
9 | Disconnect the A/C pressure cycling switch. Does the scan tool indicate A/C request as YES? | -- | Go to Step 10 | Go toRepair Procedures in Electrical Diagnosis (8A Cell 67).
10 | Using a test light connected to ground, probe the A/C request circuit at the A/C pressure cycling switch harness connector (PCM side). Does the test light illuminate? | -- | Go to Step 11 | Go to Step 17
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 completed? | -- | System OK | --
12 | Check 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 | Go to Step 17

13

1. Check connections of the A/C pressure cycling switch harness connector.
2. 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

Go to Step 14

14 | Replace the A/C pressure cycling switch. Is the action completed? | -- | System OK | --
15 | Repair the open A/C request circuit between the switch and the PCM. Refer to Repair Procedures in Electrical Diagnosis (8A Cell 5). Is the action completed? | -- | System OK | --
16 | Repair the grounded A/C request circuit between the switch and the PCM. Refer to Repair Procedures in Electrical Diagnosis (8A Cell 5). Is the action completed? | -- | System OK | --
17 | Important:: Replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Is the action complete? | -- | System OK | --