Chart C-10A A/C Clutch Control

Chart C-10A - A/C Clutch Control Circuit Diagnosis:

A/C Clutch Control Circuit:

CIRCUIT DESCRIPTION
The A/C clutch control relay is Electronic Control Module (ECM) controlled to delay A/C clutch engagement about 0.4 second after A/C is turned "ON." This allows the Idle Air Control (IAC) to adjust engine rpm, before the A/C clutch engages. The ECM also causes the relay to disengage the A/C clutch during wide open throttle (wide open throttle) when high power steering pressure is present, or if engine is overheating. The A/C clutch control relay is energized when the ECM provides a ground path for CKT 459. The low pressure switch will open if A/C pressure is less than 276 kPa (40 psi). The high pressure switch will open if A/C pressure exceeds about 3034 kPa (440 psi). The A/C pressure fan switch opens when A/C pressure exceeds about 1380 kPa (200 psi).

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.

1. The ECM will only energize the A/C relay when the engine is running. This test will determine if the relay or CKT 459, is faulty.

2. In order for the clutch to properly be engaged, the low pressure switch must be closed to provide 12 volts to the relay, and the high pressure switch must be closed, so the A/C request (12 volts) will be present at the ECM.

3. Determines if the signal is reaching the ECM on CKT 366 from the A/C control panel. Signal should only be present when the A/C mode or defrost mode has been selected.

4. A short to ground in any part of the A/C request circuit, CKT 67 to the relay, CKT 59 to the A/C clutch or the A/C clutch, could be the cause of the blown fuse.

5. If the ECM is seeing a high power steering pressure signal, the A/C clutch will be disengaged by the ECM.

6. With the engine idling and A/C "ON," the ECM should be grounding CKT 459, which should cause the test light to be "ON."


DIAGNOSTIC AIDS
If complaint was insufficient cooling, the problem may be caused by a inoperative cooling fan, or A/C pressure fan switch. The engine cooling fan should turn "ON" when A/C pressure exceeds a value to open the switch, which causes the ECM to energize the cooling fan relay. See Chart C-12A, for cooling fan diagnosis. Chart C-12A Cooling Fan Check
If fan operates correctly, see "System Diagnosis" in Heating and Air Conditioning.