A/C Request Circuit Check

Diagnostic Chart:

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 - C6O or A/C Controls - C67 and C68.

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.

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

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

5. 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 (SA Cell 67).