AC blowoff

cyberwolf · Post by **cyberwolf** » 31 Mar 2016, 09:46

I recently purchased a '98 S90 and the previous owner mentioned that the AC wasn't working properly. He mentioned that he had charged it and it worked for awhile but he then noticed a hissing noise and it quit. He then apparently added a can of freon and it was working, but only really cold at idle. It has worked fine for me since then, but again, only cold at idle. When I accelerate the air got warmer and stopped blowing. A few days ago we had our first really hot day and I was sitting at idle for 5 minutes or so with the AC on. Suddenly there was a bunch of white vapor coming out from under the hood and now the AC is not blowing cold at all.

Does this sound like it was overcharged or is there something deeper I should be looking for? I'm thinking I need to pull a vacuum and then recharge, but my AC experience is limited. One issue I'm having with troubleshooting is the lack of an obvious high side port, but I just read a little on how to connect to that, so that will be the next step I guess.

93Regina · Post by **93Regina** » 31 Mar 2016, 12:05

cyberwolf wrote:'98 S90.

On 1993-245, Volvo had a blow-off valve on back-side of A/C compressor, so when a specific pressure was reached, it would open.

So, does yours have a blow-off valve?

cyberwolf · Post by **cyberwolf** » 31 Mar 2016, 19:10

I do not see a blow off valve at all, so I'm somewhat at a loss as to where it came out.

93Regina · Post by **93Regina** » 31 Mar 2016, 19:59

cyberwolf wrote:blow off valve at all

In this FAQ, Adding High Pressure Cutoff Switch to pre-1992 Cars, they note that "In addition, if you have to replace a compressor, try to get a new one with a blowout valve."

2005 VADIS does not show this blowout valve

Smoke - Might see this thread: '98 S70: 16 y.o. A/C system presents first problem

I have all the tools/skills to fix A/C, but I don't get excited about fixing mine; in fact, on my 940, all I got to do is install a pulley/belt, but I'm not motivated, for about two years now.

cyberwolf · Post by **cyberwolf** » 31 Mar 2016, 20:42

Yeah, AC doesn't thrill me either. My symptoms of the air being cool only at idle sounds like the clutch issue you refer to, but not sure that explains the pressure release. I think the first thing I am going to do is have the system evacuated, pull a vacuum and start from scratch. Just not sure what the PO did or didn't do. I'm thinking that I could have high pressure causing the cutout, but not enough freon. My AC knowledge is limited, though...

93Regina · Post by **93Regina** » 31 Mar 2016, 22:29

cyberwolf wrote:pull a vacuum and start from scratch...

Check that FAQ site, I suspect about 3 12oz cans.

Imho, unless the radiator is good, and the other components (fans, relays, sensors, etc) have been tested, I would not engage an AC unless via highway driving.

Too much engine heat can take out your head-gasket, and transmission. A/C works fine in new vehicles, but with older vehicles, people don't want to spend the required bucks to do it right. My 1993-245, via PO, blew the HG, and he or the mechanic never fixed the problem (fan clutch shot).

hillbilly · Post by **hillbilly** » 13 May 2016, 09:04

If it blew out all of the freon, it has a leak somewhere. My 94 model 940 with the Seiko Seiki SS121DS5 compressor has a pressure relief "disc" that is screwed into the back of the compressor right beside the high pressure outlet connection on the compressor. I also, once had a high pressure hose burst while idling through a parking lot. Sounded like a gun shot with the included vapor trail.

If I was going to look for a leak, first it would be visual with a mirror. Then, I would add only one can of freon and check for leaks with a spray bottle of soapy water. Soap every hose connection, the compressor seal behind the clutch, all the hoses and pipes, the condenser coil in front of the radiator.
If you don't find the leak there, then you can look under the dash at the evaporator coil.

If you can repair the leak, be sure to add oil to the compressor along with the freon.

From the way you described the failure, the leak will be very apparent.

What is the Model and number of your A/C compressor?

Good luck