I've checked out the AC today. There is enough gas in the system and with the compressor clutch pulled in with a 12v patch lead I get nice cold air. However, the heater controls (set to cold) will not turn the damn thing on. Push the button and nothing happens including no light in the push button. However... If you turn the heater to full demist, slid the lower knob fall right, the compressor kicks in and the AC works (on full hot).

I've put a meter over the contacts on the pressure switch and see about 5v. Also, if I force the compressor on the fans don't seem to kick in reacting to ac system pressure. The pressure in the system rises higher than it should. The fans DO kick in eventually but I suspect that is due to radiator temperature and once that happens the ac system pressure reduces.

The problem is obviously electrical but with out a wiring diagram I'm not too sure where to start. Does anyone have a digitized wiring diagram or a good idea???

Regards
IanF
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At 08:04 AM 3/24/01, Ian Firmin wrote:
>I've checked out the AC today. There is enough gas in the system and with the compressor clutch pulled in with a 12v patch lead I get nice cold air. However, the heater controls (set to cold) will not turn the damn thing on. Push the button and nothing happens including no light in the push button. However... If you turn the heater to full demist, slid the lower knob fall right, the compressor kicks in and the AC works (on full hot).

Check the red/white wire at the back of the A/C switch panel for 12 vdc. If there, press the button and check for 12 vdc to the green/blue wire. If not there, the button switch is bad. If there, check for 12 vdc on the same wire at the input to the HVAC control unit. If there is 12 vdc there, the problem is internal to the control unit.


>I've put a meter over the contacts on the pressure switch and see about 5v.

Not certain of what you are testing, but it is bad anyway. If you are measuring 5 vdc drop across the switch with the compressor on, then the switch has too much resistance. If you are measuring 5 vdc delivered to the switch, then there is high resistance in the control unit or the anti-freeze switch at the base of the windshield under the plastic shield
under the bonnet.

>Also, if I force the compressor on the fans don't seem to kick in reacting >to ac system pressure. The pressure in the system rises higher than it should. The fans DO kick in eventually but I suspect that is due to radiator temperature and once that happens the ac system pressure reduces.

Sounds like a bad pressure switch. On the earlier cars, the fan switch on the receiver/dryer is a temp switch, and can be changed with no loss of freon. Unfortunately, on the '88 it is a pressure switch, and changing the switch will lose freon.


>The problem is obviously electrical but with out a wiring diagram I'm not too sure where to start. Does anyone have a digitized wiring diagram or a good idea???

Good luck. Let us know if we can help further.

Wally Plumley
928 Specialists