Symptom Chart-Refrigerant Circuit

Test Results
Compressor will not shift on.

Cause
There is either an electrical fault in the clutch circuit or very little or no refrigerant in the A/C system.

Correction
1. Check for blown fuse.
2. Check for loose electrical connector, broken wire or bad ground.
3. Check for defective combination air conditioning/fan switch.
4. Check for defective deice thermostat.
5. Check for defective diode.
6. Check for defective clutch.
7. Check for defective three-way pressure switch.
8. Switch on ignition and A/C system, then check plug of vacuum line through bulkhead in engine compartment. If no current is present, the problem is in the wiring harness to the passenger compartment or in the combination air conditioning/fan switch.
9. If current was present in step 8, check operation of deice thermostat, replacing as necessary. If deice thermostat is operating properly, check operation of diode.
10. If diode is operating properly, check operation of clutch by feeding in 12 volts directly from battery. Clutch should engage.
11. If clutch is working properly, start engine, turn on A/C, supply clutch with current from outside source, bypass three-way pressure switch and check for bubbles in sight glass. If no bubbles appear immediately after compressor cuts in, refrigerant system is empty. If bubbles are present more than 10 seconds after compressor cuts in, three-way pressure switch is defective. When performing step 11, do not run compressor for more than 30 seconds.
12. Replace defective parts as necessary, locate and repair leaks, evacuate and refill A/C system.
13. Perform operational test.