Ok,
I have an 86 and when I sit at a light the a/c blows warm. I noticed the compressor cuts off and this is due to the high side reaching 400 (glad the high side cut of switch works). The condensor doesn't appear dirty form the front. What can be causing the high temperature and subsiquently the to high pressure? I don't have a seperate a/c fan.

 

You have an air flow problem. get an electric fan and put it in the front of the condensor. I am getting ready to replace mine - I got real close to it and it has thousands of little rocks stuck in the fins.

 

May be the fan switch. It's on the high pressure line next to the high pressure switch. It will open at 230 psi which signals the ECM to ground the fan. It closes about 170 psi and the ECM will remove the ground. A quick test is to disconnect it - fan should run. Then check it with your gage set to make sure the fan is coming on at 230 psi.

 

Thanks.
Now about the fan , you know my car is only equiped with one radiator fan. NO SEPERATE CONDENSOR FAN. So you are saying the radiator fan is controled by two sources? One is the radiator temp switch and the other is from the high side of the a/c system? This would clear up the problem if this be the case.

 

Through '89, the main fan is controlled by the a/c fan switch for a/c or the coolant temp sensor for non a/c.
There is no condensor fan. The main fan is more than adequate and under control of the a/c fan switch, will maintain a high pressure of about 200 to 220psi with the added benefit of lower coolant temps.

There was an aux fan option - more window dressing and a moneymaker for GM - that should rarely if ever come on if the cooling system is right. It isn't tied into the a/c system and not having it is no big deal.

 

Ahhh,

Well the problem seems to be that the only time the radiator fan comes on is when the engine is at 223 degrees or is this a coincidence? When operating temp goes down the fan shuts off.

 

When under control of the engine coolant temp sensor, the fan will turn on at 226 degrees and then run for about 60 seconds, cycling on when the coolant reaches 226 degrees again. It was designed this way to reduce the electrical load on the alternator. When under control of the a/c fan switch, it should turn on at 230 psi and then shut off at about 170 psi. R12, at these pressures, averages about 150 degrees, considerably cooler than the coolant temps. Since the refrigerent will reach these pressures within a short time after the compressor kicks in, the fan needs to come on sooner and will, if it's much above 70 degrees, stay on much longer.

Absent the fan, the pressures are going to soar (as you've seen) and if the high pressure switch doesn't open the circuit, the engine can easily overheat, leading to even higher pressures until the whole thing blows apart. In the old days, a pressure relief switch was screwed into the rear head of the compressor that would let all the gas out when pressures got extreme. Since the late '70's, early '80's, you're at the mercy of the switch.

In any event, your fan is coming on as commanded by the engine coolant temp switch. That usually means the relay and ECM are ok. Find the switch and disconnect it and if the fan comes on, you just need a new switch. If it doesn't, something is still completing the circuit to the ECM, so you will need to check the power side of the switch for a short to ground. If the wire is ok, then the ECM is bad. Power side of the switch should be dark green and it terminates at ECM Pin D11.

 

Thank you,

So if i understand it correctly, my fan is on the engine coolant circuit
and not on the a/c circuit? It needs to come on sooner before the compressor hits 400psi. at an idle. which trips the high side safety switch.

 

Right, one circuit doesn't disable the other. It's just when the a/c is on, the a/c fan switch circuit should open when the pressure gets to about 230 psi, signalling the ECM to ground the fan Relay. If it doesn't open, then the ECM should ground the Relay when Coolant Temp Sensor indicates 226 degrees. You're real close to that on your temp gage, so that circuit is working. You need to find out why the a/c fan circuit isn't.

 

Thank you again for helping me out!!!

 

Suncr, one more question.

Is the a/c fan switch located next to the high side switch on my 86. I found the high and low side switches. BTW my parts jobber doesn't list a part number for an a/c fan switch. Do you know where I can get one?

Help?

 

Yes it's located next to the high pressure switch. Unplug one at a time, the one that turns the fan on is the switch you want. If it doesn't turn the fan on, the wire is shorted to ground somewhere or the ECM is shot.

The switch came up a month or so ago and the member had a bear of a time finding it. Try searching the a/c threads, I thought the person eventually had success. I believe I tried looking for it at the ac delco site - www.acdelco.com - but I can't remember if I found it! You can also look at the Last Detail or call them - www.tld-corvette.com - or contact the pros at www.ackits.com - they always seem to come up with just about any a/c part.

 

Thank you Suncr!!!

 

OK, Searched the recommended sites and A/C threads and can't find reference to the a/c fan cycling switch.

Any other sugestions. It is definately the culpert.

 

Great news!!
Went to an auto air shop here in Hollywood Fl. and the technician found the specs on the fan switch and found a simular switch which activates 10 psi sooner. Big deal! He also did an analysis on my refridgerant and found 90% 134A mixed with R 12. He is not an enthusiast on converting R12 systems. Says it only leads to other problems. Evac, vacuum and recharge and the system is great. Switch works like a charm!!! Thanks to all.

 

Neato!

 

Evac, vacuum and recharge and the system is great. Switch works like a charm!!!

Did they recharge with r12 or 134a?