Hi everyone - Last July, I bought a 1991 740 and I had the a/c compressor replaced because I live in Florida and a/c is crucial. It worked well throughout the Fall and Spring. A few weeks ago though, it started doing this strange thing where it would run absolutely hot/warm air and then again, the next time I used it, it would be cold again. Then days and days of no a/c to one day get in and have great ice cold air. ?!?!

Now, it switches between being an a/c and a heater several times throughout a drive.
I had the guy who actually replaced the whole thing take a look at it and he swears that it isnt his work or equipment both of which, according to him, are in perfect condition.

So what is it? I am literally home bound these days because of this because on top of it being a florida summer - I have a bun in the oven and its just too too uncomfortable!!

Of course, I plan on taking it in but I wanted to have some advanced knowledge from the smart people in here, so that I am not completely ignorant when I go to the repair shop. Or of course, if I just might have to say a special prayer or kick a tire or something to get it going ;-)

Thanks in advance!!

possible things i can think of off the top of my head:

a/c clutch sporradically engaging: possibly relay or wiring.
vacuum leak
not enough coolant/refill needed/system leaking

aaaaaaand...thats it.

Your A/C is not schizophrenic, it has a multiple personality disorder....
Joking aside, it does sound like the A/C clutch which can be replaced without having to tear down the whole system. Is the compressor making any noises when this happens?
Have you upgraded the system to R134 instead of freon?

hilarious - i think you are right about the MPD - as far as a sound: there is no sound at all. the update i think is what was done in august. when i bought the car the seller mentioned there being some sort of update to be made to the a/c system and we took it to an a/c guy and he claimed he updated it. i have gone bananas trying to locate the receipt for service so i can see what i actually paid for.

ugh - ignornance sucks.

thanks for your reply-

If it's the A/C clutch cutting on and off you should hear a definite click each time the temp changes from cold to hot. It sounds like you have the R134 conversion. Is your A/C tech telling you everything checks out at his shop? Maybe you should take him for a drive in your 740 until the cooling goes off and then he can check it when it isn't working.

Hi everyone - just thought I'd post an update for future generations. ;-)
I still havent had a chance to take it in but a volvo enthusiast friend of my dad's took a look and is convinced that the problem is a faulty "a/c switch panel" - the switch itself is bad but the compressor etc is fine and there are no leaks of any sort.

Apparently, there is a rig to get the a/c going until the new panel comes in, which he ordered at a discount auto part store.

Ok i'll keep this updated if necessary!
thanks to everyone.

Hi sarahfa,
Did the replacement control board fix your problem? If so, would appreciate ordering info/cost...

I have the same model - '91 740 wagon with the same problem. I seem to recall that this problem might be due to a faulty A/C control board, and that it might be repairable by removing, re-soldering various connections on the board, and re-inistalling. Now that I think of it, it was a dealer tech that told me this.

volvobill

volvobill, try to resolder the unit, this can save you a lot of money.
The soldering issue is very common, I was told by the A/C guy that this is thier "bread and butter" with the volvos.
http://www.volvoclub.org.uk/faq/HeatingAir...rolACNotWorking

Another common problem is bad ground connection of the compressor, check that too. (better check this first since it is a simple task).