I just read guycummins post on his A/C problem. I was having similar problems this weekend on my 85. I turned the A/C on and the compressor didn't engage. There was no power going to the connector. I didn't try to jump it because I didn't know which of the 2 connections was power to switch the compressor on. It could be low pressure, but I want to make sure the circuit is good.

In addition, I noticed the primary fan didn't come on with the A/C selection on the controls. In fact, the fan doesn't come on at all like it should. When the car hits 200 degrees, I hear what must be the auxillary fan kick in, but the one facing the engine doesn't move. I thought that was to come on first and be on as soon as you turn the A/C on? I jumped the connection at the relay and I was able to get the fan to work, so I am wondering if its the relay. There is power to the relay from the ignition circuit with the ignition in the on position. I remember there being another test for the cooling fan to determine if a switch is bad, but I can't remember what it is.

Anyone have any suggestions?

 

Look for your Receiver Dryer near the firewall( it is a canister looking item) there should be a switch installed on it. Remove the conector and jump the 2 wires together. That is the low preasure switch and it will cycle the fans and a/c compressor. If the a/c does not blow cold after you jump the switch then you have another problem if it does blow cold then you might have a bad switch.

 

OK, cool...I assume I do this with the engine running or the at least the ignition in the "ON" position.

 

Engine running... only with the engine runing and the a/c on

 

OK, I'll it when I get home tonight.

 

OK, with the engine running and the A/C turned on, I pulled the connector and jumped the 2 wires together as instructed above. The compressor kicked on. The air blowing seemed cool, but it wasn't that hot out last night and I didn't run it long enough for fear of damaging the compressor to get a really good idea. The car is probably low on freon after sitting in storage for awhile.

Anyway, like I said the compressor worked but the primary fan remained off. When I bypass the fan relay the fan works. Any other ideas?

 

When you jumped he switch out and the compressor came on didn't the fan come on with it? It should have, if it didn't you have to figure out why the fan doesn't come on with the compressor. If the fan was on and the compressor is working you prob just need to recharge the system. This also means you have a leak, don't let anyone say that the a/c system will normally loose a little freon over years time cause its BS. The a/c system is a sealed system.

 

I figured after 20 years the system would have a leak, after all its a GM product, and though experience, their A/C systems suck. I was planning on converting the system over to R134 anyway, but I want to diagnose and cure any problems with the current system now so its less of a hassle when the conversion takes place.

And no, when I jumped the wire at the pressure switch the compressor came on but the fan remained off. I'm wondering if the fan relay is bad whether it still affects the ability of the ECM to turn the fan on when it received the signal that the A/C was turned on.

I've feed power to the fan using the relay diagnostic and the fan comes on. I haven't grounded the ALCL to see if it turns on though (I can't remember which terminals to ground for that test, I think its A & B, and most diagrams I have seen are useless in that aspect). The car never gets above 210, at least according to the gauge, and the auxilliary fan works and keeps the engine cool, even in traffic.

In my 87 Firebird, I remembered an additional test for the cooling fan. You had to ground the sensor wire on the engine and if the fan turned on it was the sensor, if that didnt work, you did the relay test.

 

If the fan does not come on the a/c will never get cold. Stop diag on the a/c freon for now. Concentrate on the fans, this is where I have to bow down cause I don't know how to help you diag the fan problem.

 

So far the problem points to the fan relay so I'm going to replace it and see what happens. If that doesn't work, then I'm going back to the drawing board.

 

Sounds like it's low on gas. To check the Relay, ground the diagnostic link. If the fan comes on, the relay and ECM are probably ok. Compressor circuit needs to see 50 psi on the low side to close the low pressure switch. The circuit will remain closed until the pressure drops to 25 psi at which point the contacts open and the a/c clutch disengages. Jumpering the harness with a paperclip keeps the circuit closed, so compressor remains engaged. If there is any gas in it, you'll may see some ice form on the lines with a low charge and the harness jumpered. Fan switch - high side line - is normally closed, but opens at 220 psi signalling the ECM to ground the fan Relay. Disconnect the switch and the fan should come on. It will reclose at 170 to 190 psi and the ECM removes ground from the Relay. All in all, it probably doesn't have enough pressure to make it work; ie, it needs a recharge.

 

Thanks! Seems like a simple test and solution. What terminals on the diagnostic link do I ground?

 

A to B or the two upper right hand terminals looking forward.

 

Thanks....I tried it, fan still doesn't come on. Redid all the tests per the diagostic chart and according to the Haynes manual and all tests point to the relay as the problem. Now I just have to find one. All the parts stores around here don't have any. I have one more place to check and if I strike out there, it looks like Ecklers or Corvette Central.

 

I'm pretty sure NAPA carries them. If you haven't done so, you might want to jumper the fan directly to power and ground to make sure the motor isn't shot.

 

I actually did that and the fan works. Also, I noticed there are 2 senders in the heads. The sender on the passenger head contains the green wire which I believe is the temperature sender for the fan, correct. However, there is another sender, this one in the driver's side head with what looks like a blue wire. I can't find it in the manual, what is this sender for?

And I tried 2 NAPA stores in my area and both don't have it.