Component Diagnostic Charts/Tests

Fig. 012 Chart C-10 A/C Clutch Control (1 of 2):

Fig. 014 Chart C-10 A/C Clutch Control (2 of 2):

Fig. 015 - Wiring Diagram for Chart C-10A A/C Clutch Control. VIN P:

CHART C-10, A/C CLUTCH CONTROL

Ignition voltage is supplied to the A/C control relay through the A/C and pressure cycling switch on CKT 59.
A circuit 59 splice applies voltage to the ECM Terminal B8 through a 30 ohm resistor wire limiting the current to the ECM.
When voltage is applied to Terminal B8, the ECM will delay about 1/2 second then ground Terminal A3 and close the relay. The delay is to allow time for the ECM to increase the idle air rate and provide a momentary air/fuel enrichment to offset the compressor "turn on" load.
The ECM also monitors engine coolant temperature and will turn off the A/C if engine temperature is above 120°C.
1. Confirms that fault is system electrical and not due to loss of refrigerant.
2. This and following steps check for ECM control of relay and if relay is causing problem.




3. There is a "Low Vacuum" switch connected to ECM Terminal B8. If power brake vacuum is too low, the switch will close to ground and turn "OFF" A/C. This test is to remove this switch as a possible cause for no A/C should the switch fail to open with engine running.
4. This check requires the use of a high impedance voltmeter. The 30 ohm resistance wire limits the current to approximately .1 Amp to prevent damage to the low vacuum switch when it is closed. This is not enough current to light a test lamp.
5. Solenoids are turned "ON" or "OFF" by the ECM internal electronic switches called Solenoids are turned "ON" or "OFF" by the ECM internal electronic switches called "drivers". Each driver is part of a group of four called "Quad-Drivers". Failure of one can damage any other driver within the set.
Solenoid coil resistance must measure more than 20 ohms. Less resistance will cause early failure of the ECM "DRIVER". Using an ohmmeter, check the solenoid coil resistance of the following before installing a replacement ECM.
- Canister Purge Solenoid
- A/C control relay. Pins opposite harness connector Terminals "B and C".
- EGR solenoid