A/C Fun Please help (Long, but detailed for better help)

Aramelli · Post by **Aramelli** » 20 May 2010, 07:39

Okay, I have a friend who is a mechanic by profession. He normally works on domestics and asian cars. Volvo is not new, but he does not like them. I was getting sick of the A/C not working in this hot weather, so I took my vehicle to him and did the labor while he worked on other cars, and he would come help me if needed. We changed the hose from condensor to evaportor, because there was a leak. Then we vacuumed the A/C system and added oil and freon. After ten minutes a bunch of freon just escaped from the compressor. My friend, the mechanic changed the high pressure release valve on the compressor off of one of the compressors that were sitting around in his shop.

The whole time we were doing this we rigged the compressor to come on, because it didn't always come on with the AC switch inside the car(Meaning it would sometimes). I read about an AC relay located behind the glove box and told my mehanic that could be the problem. We took it out and tested it and the relay was working fine. What we realized is that main wireing to the power stage didn't work with the swtich, because it wasn't grounding properly. He says he has to follow the whole system and find the kink in the wire. We temporary grounded it ourselves and would get the compressor to kick on with the switch. One problem is though, that the FAN wouldn't come on when the AC came on. After doing abunch of test on different wiring by the fan he said that he had to call an electrical friend of his out to look at it.

Does anyone know what my problem could be?
-Ground sometimes on AC switch
-Fan not properly working with the compressor
-All wiring to the fan relays are on good, and he said the relays are also good.

Post by **JDS60R** » 20 May 2010, 08:29

I would get the missing ground fixed first. If its a constant ground your friend can run a new one. If not- then finding the break is the right thing to do. Once everything is plugged in you can see if the fan works correctly. The wiring diagrams are available here so you can trace your grounds to check points.

A second concern is adding oil. The oil normally settles to the bottom and you replaced the top hose. If you replaced more oil than you lost you may have too much oil for the system. Some recovery systems can measure and regulate the amount of oil and perhaps he used that machine. I wasn't sure how you knew you had the right amount of oil so I figured I would mention it.

After looking at the diagrams many of the grounds are regulated by the ECC. If you can explain which ground is failing we could suggest a reapir vs replacing the ECC.

Post by **JDS60R** » 20 May 2010, 08:49

Perhaps your friend dumped out the oil whaen the replaced the valve on the compresor. I am going to go have my coffee now. Sorry I missed that.

Post by **Ozark Lee** » 20 May 2010, 14:28

The fan won't come on until the high side pressure gets up to a certain threshold. Since we have no high pressure service port on the car I am not certain what that pressure is.

The way the system works is that the A/C switch turns the A/C relay which supplies battery voltage to the compressor via the low pressure switch. Once the compressor kicks on and builds up high side pressure the high side pressure switch signals the ECU that the A/C is on. The ECU then issues the command to turn on the fan via the fan relay which is on the fan shroud. The fan relay is a high failure rate item.

Before the system purged itself was the A/C blowing cold?

...Lee

Aramelli · Post by **Aramelli** » 21 May 2010, 22:16

We had a specialist come out who's sole job was electrical work. He pinpointed the issue to the Drier sensor. He said that the sensor is responsible for sending a command to the Fan or perhaps the ECU then fan. It's located right by the R-134 pressure valve, behind the headlight. Tomorrow I will take a picture and post it. The AC system appears to be working now.

A problem that has happend a couple times is that when i switch the temperature, a bunch of cloudly stuff comes out of the vents. I think it's freon, but when i checked the pressure it was at 40PSI. Any ideas?

Post by **polskamafia mjl** » 21 May 2010, 23:24

This happend on my friends 20 yro Acura. He claimed it was just water vapor. I haven't found a better explanation so far.

Aramelli · Post by **Aramelli** » 23 May 2010, 21:42

Picture of sensor that was bad. This sensor triggers the fan when the compressor is turned on.

Uploaded with ImageShack.us

junkcollector · Post by **junkcollector** » 02 Jul 2010, 14:53

This sounds very similar to a problem on my '96 850. The A/C blows nice and cold for about 6 minutes and then the power is cut to the A/C clutch and the air blows warm. I find that if I turn off the A/C on the console while driving, after a few minutes, I can turn it back on and get more cold air - this only lasts for a few minutes as well.

I've read various posts that suggest this is the high pressure switch, but I'm not convinced that's at fault. It could be that the shroud fan is simply not coming on and the A/C high pressure switch is shutting off the compressor because the system is running to hot (increasing the pressure). That would also fit with the symptoms - letting the system cool while I drive (instead of the fan doing its job) is what may be lowering the tempreature/pressure enough to let the A/C compressor come back on and give some more cooling.

So maybe the fan relay, or maybe the dryer sensor, as suggested here. Does anyone know when the aux shroud fan typically turns on for the 850? Yes, it's getting hot in FL these days

Post by **Ozark Lee** » 02 Jul 2010, 21:33

Welcome to MVS,

Your problems sound very much like an issue with the AC clutch gap. I am on dialup or I would post you a link. I put together a bunch of very good links to diagnose and fix the clutch gap issue and it is pinned in the repair database. Perhaps another member with real internet access can post the link for you.

...Lee

Post by **egads** » 02 Jul 2010, 23:09

Here we go.

Clutch Gap Fix