Part 1 of 2

Chart C-10 Part 1 Of 2:

A/C Circuit:

Circuit Description:
The A/C compressor clutch control 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 compressor clutch engages.

The PCM will engage the A/C clutch anytime A/C has been requested unless any of the following conditions exist:

^ High coolant temperature.
^ Wide open throttle.
^ High engine RPM.
^ High A/C system pressure.
^ Low system pressure.
^ Any A/C DTC set.

The PCM determines A/C has been requested by receiving a voltage signal from the A/C control head. When the A/C control switch closes, the A/C request input has 12 volts applied to it. This is shown on the Tech 1 as A/C request "YES." A 3-wire A/C refrigerant pressure sensor is used to monitor A/C system pressure. If the A/C refrigerant pressure is greater than 430 psi or lower than 0 psi, the A/C clutch will not engage.

A faulty A/C refrigerant pressure sensor will set a DTC 66 or 67. If the A/C refrigerant pressure sensor signal wire becomes open or shorted to ground, DTC 66 will set. If the signal circuit is shorted to voltage, a DTC 70 will set. If the A/C clutch engages and no pressure change is detected, a DTC 67 will set.

When a request for A/C has been detected by the PCM, the PCM will ground the A/C compressor clutch control relay drive circuit, the relay contacts will close, and current will flow through the relay to the A/C compressor clutch.

Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.

1. Checks the PCM's ability to control the A/C clutch control relay.

2. Checks for grounded CKT 459 to PCM.

Diagnostic Aids:
Before using CHART C-10, be sure no DTC(s) are stored. The PCM will not energize the A/C compressor clutch with a stored DTC.