1993 940 A/C questions
 

I'm hoping someone can help me with this. I've read the most recent A/C posts and not quite the problem I'm having. My A/C was dead so I got one of the cheap diy cans with a gauge and jumped the compressor and got enough in there to at least get it cycling. Then I got some gauges from Autozone and hooked up a bigger bottle and proceeded to fill it up but I forgot to look at the sight glass just to make sure it was going in. At this point I've got the lowside pressure up to 28 - 30 psi and the vent temp is 52 degrees. But that's it, it won't take anymore. The can is releasing and the valves are all open. Shouldn't it take more? My dryer is showing real cold, wet condensation. It's about 72 degrees outside and about 40% humidity. The charts I've seen show higher pressure than what I'm getting. The only thing I didn't do is hook up the hose to the high pressure side. My search shows that some people think the 940's don't have a high side port, while others say it's on the back of the compressor{top side). I do see a cap there that looks like a port cover but as soon as I started to unscrew it I heard gas escaping so I tightened it back up. Any idea what's going on? Thanks

if your system was out of freon, it should be evacuated and leak tested before it can be charged. if it was completely out for a long time, odds are the receiver/dryer is contaminated and needs to be replaced. I leave AC servicing to pros who have the right equipment.

I don't have my chart handy but at 72* I'm thinking you should have maybe 40-45 psi on the low port. A trick I use it to take a pot of hot water and while you are charging put the can of freon in it. It will flow into the R/D quicker. Also put a box fan in front of the condenser and jury rig the throttle to get 1200-1500 rpm. Now about the vent temp. 52* is not bad so far which shows the system is operating. But it may not get colder until you drive it and get more air going through the condenser. Another question is the auxiliary fan working when you turn on the AC. Now let the system sit for 24 hours and take another reading. If the pressure goes down you have a leak so go down to your auto parts store and get a can of freon with dye in it. Also get a cheap Black lite and see if you can find the leak. If you find it then you'll need to start replacing parts and flushing the system. Good luck and keep us posted

I understand what you're saying and normally I would do that but this is sort of a learning project for me and I've always wanted to learn about A/C systems. And luckily, parts are readily and cheaply available if I screw something up.

UPDATE: I drove around for a while and checked the readings again. The fan comes on and it's a steady 30 lbs, which I understand is pretty good but I'd like to get "ice cold" A/C that everyone talks about. One thing I did notice is when I disconnected the gauge hose from the low port the Schrader valve was slightly bubbling. So that's an obvious leak and probably why it lost it's charge in the first place. But once the gauge hose is connected that shouldn't restrict the amount of 134 going in? I'll watch it and recheck in a couple of days and if it's loss it's charge I'll replace the Schrader valve. Any DIY tutorials on that? And then I'll dbl check with dye and a blacklight.
Also, I've watched a few Youtube videos on Volvo A/C and no one seems concerned with hooking up the high side gauge. I'm guessing because it's on the compressor. Do most A/C shops ignore that on Volvos? And why do you think my high side port started releasing gas when I started to unscrew the cap? The Schrader valve under that has to be shot too don't you think? Thanks

OK lets get on the same page here. What did you mean with regards to the 30 lbs while driving around. The coldest duct temp. that you should normally see will be around 45*. That would be considered "ice cold" by car AC standards. To get colder risks the evaporator to get frozen. Now about the hose connection (low pressure) on the receiver/drier , it is normal to see bubbles upon removal of the connector. Just wipe it with a rag and check it with a little soapy water to see if it continues to leak. Most backyard mechanics don't use the high pressure port but for a total system check it should be used. Auto AC on cars is fairly straight forward except on climate control systems. You just need to respect the system and take safety precautions. Some freons are flammable and they all can freeze/contaminate your eyes . You also need to watch the pressures. There are plenty of articles on the web about AC systems so just read and you will learn. In the 25+ years and 350K miles we have on our Volvo I have replaced EVERY component on my AC system except the evaporator. I would have still liked to keep R12 but the enviro types stopped that here in NY. Replacing it with 134 works OK but is inefficient for a system designed for R12.

Sorry, after I drove around I checked the pressure and at idle it was 30 psi on the low gauge at idle. I'll double check the bubbling on the low side. My totally inexperienced hunch is that I may not be able to pressurize the system above 30 psi and get my vent temp down to 40 something because of the leak under the high port cap. If it's releasing gas when I start to unscrew it then it's got to be worse then just bubbling and I don't believe the cap secures tight enough to stop a leak. Is that feasible? A major leak would prevent the system from charging at all but I small leak would allow to charge up to a certain pressure and no more. What do you think?

OK lets do a reset here. Is the system 134R freon. Are you plugged into the low pressure port on the receiver/drier . Do not put anymore freon in to the system. Wait 3-4 days and then check the pressure with the engine off. What is the pressure.
If you have a major leak you won't be able to get any freon into the system and you should be able to hear it leaking. If you have a minor leak you will lose pressure(freon) over the course of a few days. Let us know after a few days what you have and we will go from there.

FYI keep this chart handy R-134a System Pressure Chart | AC Pro

All cars sold in the US beginning with 1993 MY are R134, by law, just like all cars starting in 1996 are OBD2, by law.

Yes, I'm setup for R134. I'll check it in a couple of days and see if I lost anything. Thanks