Air conditioning faux pas

somehow my AC leaked all the freon out. I put a vacuum pump on it and let the air out of the system then added freon but it appears there is a valve between the high pressure side and the evaporator that is not working to let any fluid through. I wonder if this is something that can be disassembled and cleaned or repaired. It appears to be under the dash somewhere. Anyone ever take one apart?

Bob in Lake Havasu

Bob, have you completely evacuated the system and proven it will hold said vacuum (no leaks)?

alan

Yes, it holds vacuum. It holds the freon inside too. Just when the compressor runs, the low side is too low and the high side is too high. The compressor shuts off on high pressure and the air coming out of the vents is warmer than ambient.

Bob in Lake Havasu

Bob, a good friend of mine is an ex-factory certified BMW tech. He is on vacation for the next 2 weeks but if you can wait, I will pose this scenario to him. Have you done any research online? Wonder if it is indeed the compressor as the rest of the system is passive (plumbing and such) or the part of the compressor that regulates internal pressures? I also wonder if the pressure sensor in the compressor thinks the pressure is too high when it is really at a normal level and therefore shuts down the system?

It am sure the pressure is hitting the high pressure limit because I can hear the belt start to squeak just before it shuts off. I measured the low side pressure and it was 100 psi on an 80 degree ambient day. As soon as I started the compressor the low side decreased quickly to near zero. The temp of air coming through the vents was 90F. So the low side is too low and the high side is too high.
There is some kind of valve showing on Realoem.com but very sparse detail of it. Nothing in Bentley about it.

Bob in Lake Havasu

A couple of weeks ago, the AC at the house shuts down. As in your case, the high pressure switch (resetable) tripped. Turned out my condenser fan had seized. Replaced it and the system was back to normal. I wonder if something in your system might be clogged which is preventing coolant circulation to the condenser and that is causing the high pressure shutdown?

I had a pressure gage on the low side and while the compressor was running the lowside was too low. When it stops, the pressure rises a bit but the high side decreases only enough to let the compressor restart for a few seconds. If I leave it for a long time the low side increases to about 100 psi. I am sure something between the condensor and evaporator has shut off the flow for sure. Air coming out of the interior vents is warmer than ambient. There is some kind of valve under the center dash and glove compartment somewhere but I am not sure if it has any parts that can be replaced or not .

Bob in Lake Havasu

The expansion valve is right beside the evaporator on the passenger side (LHD cars). You have to take the glove compartment and the trim pieces on the left side of the glove compartment out to get to it. It's connected in two places to the evaporator and has two hose connections. I've had mine out and apart and I'd be surprised if there was anything blocking the flow inside it. I suppose it's possible, but it doesn't seem likely. If you remove yours, to open it up you remove a plug from the end of it, it's threaded. Inside there's a ball that's about 1/4" in diameter, a short heavy spring, about 1/4" to 3/8" long and about 1/4" OD, and a tapered rod, about 1" to 2" long and about 1/16" in diameter, with some variation in diameter along the length. I'm pretty sure the rod moves back and forth against the ball and spring to vary the amount of open space in the valve. I don't think it could get stuck in a position that would block the valve. Maybe something got in the valve somehow, but the question then would have to be where that stuff is coming from. There shouldn't be anything inside the A/C system that could block the valve.

If you do take it out, replace the o-rings before you reinstall it. The o-ring under that plug on the end was where I lost a couple of charges of R-134a before I figured there was an o-ring in there.

You'll need a couple of big adjustable wrenches, or a good collection of big wrenches to get the valve out. The connections to the valve are big.

John

Thanks John, you must be the only person that has ever taken one apart. The o-ring you mentioned, did you have trouble finding one compatible with R-134?

Don't know what might be clogging my valve but suspect the conversion to R-134 was not done very well. It was part of a reconstruction after an accicent. The dryer sight glass has had some kind of mud on the inside since I got the car. Probably need to replace that too. Thanks for the description of what is in there, looks like it will take some planning to have all the parts for it when I tackle it.

Bob in Lake Havasu

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Bob in Everett
Thanks John, you must be the only person that has ever taken one apart. The o-ring you mentioned, did you have trouble finding one compatible with R-134?

Don't know what might be clogging my valve but suspect the conversion to R-134 was not done very well. It was part of a reconstruction after an accicent. The dryer sight glass has had some kind of mud on the inside since I got the car. Probably need to replace that too. Thanks for the description of what is in there, looks like it will take some planning to have all the parts for it when I tackle it.

I only took it apart because the one I bought as a replacement for the R-134a conversion had one connection that was the wrong thread. I was pretty amazed at how simple it was inside. I forgot to mention that the plug has a little hole in it that you have to use to unscrew it. I put a punch in the hole and tapped against the side to unscrew it. It wasn't totally obvious that it would come apart like that. I think the replacement I didn't use must have had a hex head on it and that clued me in.

I bought neoprene o-rings at my friendly local hose shop that also made me a new pair of hoses to connect to the compressor. The o-rings were green for easy visual ID of the material. I just took in all the old ones and got new ones to match. There's about 14 or 15 all together I think. They come in black too, of course, but neoprene is the key to happiness with R-134a.

I would go ahead and replace the dryer too if you don't know it's history.

Have fun. I bet you'll get it all figured out in time for that nice cool fall weather.

John

Yes, that is true. Right now I just put the top down instead.

I had a "perfect" opportunity to do all that stuff when I had the radiator out last summer but was a bit discouraged at the time so was trying to get it back together just to see if I had found the right answer to the coolant getting into the oil. Glad to say that coolant is staying in the reservoir and the oil is staying where it belongs. I did use that opportunity to pain the valve cover and intake and make them look nice.

Bob

Bob in Lake Havasu

Just took mine out the other day. Hit the A/C-no joy. It was recharged about 2 years ago. I guess I need to take it in and find out exactly where it is leaking and get 'er done. Had the same issue with my daily driver, turned out it was a bad hose.