Chart C-10 A/C Clutch Control Circuit Diagnosis

Chart C-10 - Part 1 Of 2.:

Chart C-10 - Part 2 Of 2.:

A/C Relay Circuit.:

CIRCUIT DESCRIPTION
The A/C clutch relay is Powertrain Control Module (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 CKT 459 to energize the A/C relay. This is shown on the Tech 1 (or equivalent) Scanner 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 429 psi or lower than 0 psi, the A/C clutch will not engage.

The A/C refrigerant pressure sensor uses PCM DTCs 66 and 67. If the A/C refrigerant pressure sensor signal wire becomes open, shorted to ground or shorted to voltage, DTC 66 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 clutch relay drive 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" unless vehicle speed is too high.

CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. Checks the PCMs ability to control the A/C clutch relay.
2. Before replacing C68 A/C control components, refer to Heating and Air Conditioning.
3. Checks for grounded CKT 459 to PCM.

DIAGNOSTIC AIDS
Before using Chart C-1O, be sure no PCM A/C DTC(s) are stored. The PCM will not activate the A/C clutch with a stored A/C DTC.