AC worked, then died on trip
 

Hi all,
now that the weather is getting nice, I'm sure we'll see more AC-related problems. Here's mine: 96 850 with ECC, went on a 5 hour road trip. First time turning it on this season, AC worked just fine for about 2 hours or so, then it just stopped blowing cold. It worked fine all last summer, and it didn't feel like it slowly died but suddenly (outside air was about 80 degrees). So I got it back home today, and I couldn't get the clutch to turn with the "bump it with a broomstick" method. I went to see if I could add some refrigerant, and the pressure gauge was showing a high (approx. 100psi) reading. It wouldn't let me pump any in for obvious reasons. Anybody have any ideas?

Bob

to add freon you need the compressor running. Try jumpering the low pressure sensor first - its high up on the return line from the firewall. A paper clip works fine. That should allow the compressor to kick on. Note that with the compressor off you will get a false high pressure reading on the low side. If jumpering the low pressure switch doesn't kick on the compressor, then I'd look at relays/fuses next and get a closer look at the clutch to see if it can be moved manually.

If he really does have 100 psi not running, and the broomstick doesn't work, then I am going to guess there is a "real problem" of some sort with the control system. Hopefully it's just a bad relay that's cheap and easy to get to.

A quick update; this morning while the engine was cold, I was able to spin the clutch freely by hand. I don't have any feeler gauges, but the gap does not look too big (I know, you can't really eye it up). Anyway, I started up the car, turned on the AC, and the compressor turned on. I was able add a can of refrigerant, and the psi was pretty much where it needed to be (not sure what the previous 100psi was about). So, perhaps it was just a problem of not enough refrigerant? And the car/ambient temp was cool (65 degrees). I'll know more as the week goes on, and I'll check back if I have any more problems.

good deal - you want somewhere about 50 PSI at 65 degrees when you test the low port with the AC running but that value will change some with ambient temperature so best to find a chart that quotes a full charge by air temp. Yeah the 100 PSI is a false reading you get when the compressor is not running as the low and high will balance to a number higher than the running PSI. If the AC works now then say fails on a warm day or after 15 minutes, then you probably need to shim to close up the clutch gap (what happens is when the gap goes over .8mm the clutch slips and overheats and shuts off. when it cools down it will work again. You want to get it back to about .4mm

http://www.matthewsvolvosite.com/dow...V70-AC-Fix.pdf

This is most likely the compressor clutch. As mt6127 said, as the clutch gets hotter the strength of the magnetic field lessens. An A/C system running fine will stop working when hot because the clutch can no longer build the required magnetic field to engage the pulley. The system cools off and it works again. It always dies when you need it most. Shimming the clutch moves the plate closer to the pulley and the gap is small enough that the magnetic field is enough to engage again. 3 of my 850's are shimmed for this exact problem.

Thanks for the responses; I figured it was a shim problem, so we'll see what happens when it gets warm again...which may not be for awhile lol. I'm also dealing with a laundry list of codes from the ECC, so I may be posting some questions on that later as well.