I have a '92 740 wagon that the A/C suddenly quit working on. I ran the AC for a full day one day last week; worked fine... today I turned it on, but get nothing but hot air. The compressor is cycling, although they are short cycles, and it doesn't seem labored when it does switch on. I know my way around a car, but have very little experience messing with AC. It has had the Volvo R134a retrofit (not a 3rd party kit) done, sometime long before I owned it.

Thoughts?

 

I put a gauge on it while it idled; when the compressor is off, it runs at about 40psi, (toward the top of the "full" range), then when the compressor switches on, it drops to about 20 psi (the top of the "low" range)... does this indicate any specific issues? With the engine off, it indicates about 80psi.

 

If you're still running R12 (which I recommend) 20 PSI is too low when the engine is running, the short cycling is another indication. Most probably, you've developed a leak somewhere.

 

Reread the post and saw that it has been "converted". The molecules in R134 are much smaller than R12, so unless you, or whoever, replaced the hoses with the new barrier hoses the refrigerant will seep through the hoses over a period of time. You could just recharge with R12, which your system was originally designed for, and get better cooling, although if the system has been cooling "okay" and then suddenly stopped, you probably do have a leak. Step one is to get, or do, a leak test. This is best done with an electronic leak detector, as dyes are only good for showing leaks that occur where you can see them. Lots of leaks -evaporator core, which is up under the dash, for one - are not easily seen..

 

From everything I've read since I posted, the pressures I got, both running and static, suggest the system has at least some charge... plus the low side line gets cold fast and builds condensation within a few seconds... I would think there should be at least some cool air, if not cold; wondering if maybe the air gate is stuck or something (that would explain the sudden change). New to Volvos though, are they vacuum or electronicly operated? Also not sure how to get to it to check.

 

I had some time today, thought I'd troubleshoot some more, only to find that the compressor isn't switching on now; hooked the gauge up and the gauge barely moves from 0. Tried to charge it, but it won't take a charge without the compressor running, or so it seems. Can I jump the compressor to get it charging?

 

There is a low pressure switch on the receiver/drier can. It should look like a black mushroom. Unplug it and put a jumper in the plug. This will turn on the compressor. If you have 0 pressure in the system I would get a vacuum pump and pump it down to see if you have a major leak here. No use putting in freon if you have a major leak.

 

Thanks, I'll give that a try. I want to see if it works once full again, before I start shelling out money to have it repaired (unless it's something I can fix myself). If it doesn't work once it's full again, or doesn't take a charge, then I know it's more than just a leak and will likely be more pricey that I can afford right now. A couple of $11 cans of 134a isn't a huge deal.

 

I hooked up the refrigerant and jumped the compressor; the gauge said it took a charge immediately... although I'm skeptical because it didn't take the whole can before it said it was full. I plugged the switch back in and the compressor came back on on it's own and continued to run, not doing the quick-cycling that it did a couple of weeks ago when this all started... however, still no cold air from the vents.

 

Do you have a set of AC gages. If so what pressures are you running at idle. What is low and high pressure. The orifice vale may also be plugged and may need to be changed. If you have to do this then you'll need to clean the system and replace the receiver/dryer and the orifice valve. By the way what system do you have , is it the climate control (auto) or the plain old manual AC system.