If the temperature outside is say 50 will the ac even kick on when turned on? Also is there a A/C relay? I'm trying to get my ac working before summer since the car is black, System is charged, i reshimmed the compressor but it is still not kicking on. any suggestions?

 

Bad high pressure switch, bad low pressure switch and/or A/C relay. There is one behind the glove box and I think one under the fuse box near where the fuel pump relay goes? I know my 94-850NA with MCC has one behind the glove box. I have only seen it on a schematic for my model car. I had some trouble with my A/C but found the problem before I got into having to pull the GB. Hope this helps!

 

how can you test the switches? and also what was your issue?

 

Yes, Rickford, please post more details. My also black '97 850 N/A wagon has also a non-working A/C. I have the MCC, and when I push the A/C rocker switch, the little blue light turns on, I can also hear the compressor kick-in, but then it keeps kicking on-off repeatedly and of course not cold inside the car. The fan works great at all speeds.

Thanks

 

From memory there is indeed a relay behind the glove box for the A/C (one relay is blower speed 4, the other is the A/C. There is also a low pressure switch on one the lines near the firewall which must be closed for the compressor to run. The radiator fan relay is also tied into the system, when you turn the A/C on it should also turn on the radiator fan.

The compressor kicking on and off repeatedly is an indication you are low on charge, a compressor not coming on at all is a likely indication that 1) you are very low on charge 2) the relay behind the glove box is bad 3) the pressure switch is bad.

And don't worry, the glove box is easy to pull!

 

the charge is good i checked it the other day, i definitly dont want to throw money on a pressure switch unless i know its bad anyway to check it?

 

Sure, strip back a little insulation on both wires on the pressure switch, use a clip lead to bypass the switch. If the compressor clicks on the switch is bad, if not the trouble is elsewhere.

 

Okay, mhutchens mentioned where the low pressure switch is and how to check it. Jump the two wires together and see if the compressor starts. However this did not work for me. From the beginning......

My compressor was cycling on and off every 5 seconds or so and I knew it was low on Freon, it would just barely cool. I had difficulty connecting the hose to the low pressure valve near the front passenger side of the engine and some additional freon escaped before I got it to click on. After that the compressor would not work at all. At that point I wasn't sure if I screwed up something else or if the little bit that escaped took it so low that the low pressure switch kick in (or out) and shut the system down. I inquired (as you have done) about the location of the switch and tried to jump it and still the compressor wouldn't start. After seeing how complex the system was with the relays that exist etc. and seeing that the light on the compressor switch still lit up, I decided to just jump the compressor clutch direct to the + side of the batt to see if it clicked in, and it did. (By the way the pressure reading on the gauge was 20psi with nothing running.) So I connected the freon, started the car, jumped the compressor clutch to the battery to start the compressor and filled the system to 40psi. (I cycled the compressor on and off a few times, mostly on of course, to make sure I wasn't over loading anything) and the A/C was ICE COLD (38 at the center vent). I reconnected the compressor clutch wire to its proper connection and it all worked perfectly. It's been two weeks and everything is fine!

I don't know why jumping the low pressure switch didn't work? It should have!!! Maybe I didn't have a good connection between the two wires? I used a paper clip and shoved it in the two holes of the connector that go on the switch. Maybe you have to actually strip and jump the wires as mhutchins mentioned??? Anyway, the first thing I would try is to disconnect the compressor clutch by separating the connector that is clipped directly to the side of the compressor, not the other one, and jumping the compressor side of that wire directly to the + side of the battery. You don't have to have the engine running. Just touch the jumper to the battery for a split second and listen for a very noticeable "CLICK" from the compressor, if you hear it hook a gauge up to the low pressure connection and read the pressure with the engine running and the compressor on. At 70 degrees OUTSIDE temp. it should read between 35 and 40 psi. if it does it's full. I guess that's a little more than two cents worth...hope it helps!!!

BTW this is a 94 850 NA Sed w/175k miles. Never had a recharge and the previous owner refused to run the A/C. After 17 years I think the seals just got a little stiff. I used freon with leak stop in it and everything seems to be fine, no pressure drop in two weeks.

 

after a full can of charge the compressor actually stays one and finally got cool inside the cabin, now after i turn the AC off the compressor cycles on and off for a while is that normal? i have to do one more charge it was at the bottom, haven't touched the AC since i bought the car till now and thats been 2 years

 

If you run the defroster it will use the A/C to pull the moisture out of the air. Even with the A/C off it still will run it on its own.

 

Boxpin, will the compressor run on defrost even on MCC? I know it would on a ECC? Don't remember if 91shelby has an MCC or an ECC? Just curious, I'll have to try it when I get home today!

 

I have a car with and without...I will test today.

 

All Volvo's since '82 will turn on the compressor when on defrost.

 

if your a/c compressor was NOT running when you charged it ,its not charged .find your low pressure switch and put a paper clip in it to jump it ,the compressor should now start , NOW charge your system ! now .... if you have it properly charged and you put the LPS back on and the compressor dosn't start ..... bad low pressure switch . now you got to dump the system change the switch and recharge or just leave the paper clip in , if you just plugged your gauge on and saw 35lbs with out the compressor running you have a LOW charge . i'm a A/C tech

 

Agreed. Low charge.