A/C does not hold charge

[britdog]

'tis the season...:cool:

My A/C has not worked since I bought my car last summer. Here's the history from the guy I bought it from:

When I first started having problems, I had it charged and it only lasted about 2 weeks. I brought it back and he said it had a hole it that Ray Charles could have seen, and he actually fired the guy who originally fixed it. He filled it again, and then 3 weeks later same thing.... the compressor was not kicking on.. He said an O ring had a leak and it was only a slow leak but the system has a safety shut off (low pressure switch, I presume) that turns the compressor off even if it is a little low. This kept going on for awhile..... So every few weeks I had to bring it back and leave it for a few days. I think the longest I got it to last was 5 weeks that summer. After awhile he only charged me for the coolant, not labor, but it was still expensive. The next summer same thing happened, I was determined to get it fixed, seeing how much money I spent on it. He finally referred me to the dealer saying he was stumped, it was leaking from somewhere and when it got a little low the system would shut off the compressor.

My mechanic said that a just a charge is like $150, so I'm hoping that there is some sleuthing I can do myself. He mentioned that sometimes the low pressure switch is the culprit. Is this a common thing to go?

I'm looking for suggestions on what you've commonly seen as trouble areas...places to start. Are there sections in the system that are prone to leakage and how can you find a leak?
I heard that with the old R12 systems, leaks were easier to detect, but with the newer systems, they are almost impossible to find.

Thanks for any advice!!

[OEM_TA]

$150 for just charging even a completely empty system seems high to me.
R134 runs about $12/can here. There is a 'sniffer' tool that my mechanic used to find my leak. Turned out to be a few bad o-rings. Had them all replaced and the system charged for $130.

There are 'sniffer' tools, my mechanic used one to find my leak.
Here is one there are bound to be others.
http://www.sjdiscounttools.com/tifxl1a.html

If you can buy or borrow one of them, then put enough R134 in your system to overcome the low pressure switch you can pinpoint the leak point(s).

Or since there is no charge on the system now you may be better off to change all of the o-rings yourself and get a device to pull a vacuum to make sure you got them all sealed and then either charge it yourself or take it to have it charged.

JC Whitney has an inexpensive vacuum pump that runs off of air compressor.
http://www.jcwhitney.com/webapp/wcs/stores/servlet/Product?storeId=10101&Pr=p_Product.CATENTRY_ID%3A2004193&TID=231000000&TID=231000000&productId=2004193&catalogId=10101 (http://www.jcwhitney.com/webapp/wcs/stores/servlet/Product?storeId=10101&Pr=p_Product.CATENTRY_ID%3A2004193&TID=231000000&TID=231000000&productId=2004193&catalogId=10101)
You may be able to borrow or rent one of these also.

[MaDmaXXX]

GM V5 compressors are known to leak at the front shaft seal and the compressor body seals. Alot of times the high side line from the condensor to the accumutator gets eaten by battery acid. Expansion valve orings leak alot. Look in your local paper for someone runing a special.We do free a/c checks where i work and only charge 69 dollars for an evac and recharge.

[britdog]

Yeah, I thought $150 for a basic charge sounded high. I've had good experience with this shop and trust them, so I'll have to circle around with them again on this.
In the meantime, I'm going to plan to doig the o-rings myself. Not sure how to run a vacuum for this purpose and I don't have an air compressor yet. No rush though. this will probably end up as a winter project.

MaDmaXXX, I will take a look at the compressor and the lines going into and out of it for corrosion, as well.

I'll have to dig into my Chilton's A/C section to hopefully find some clear instructionson where all the o-ring locations are. Any suggestions for other sources of information that help?

[MaDmaXXX]

anywhere that you see a fitting there are orings. the compressor has 2 the line that connects the condensor to the compressor has 1, the condensor to the accumulator has one, the accumulator to the expansoin valve has one, the expansion valve has 2, the return to ther compressor has one. They are all different sizes. Napa,Orielly,autozone, they all sell kits. while you have the system open its a good idea to replace the accumulator. There is a dessicant bag inside that traps moisture. when you open the system ,you will be letting moisture in. Have your local a/c shop evacuate the system. then change all your orings, and replace the accumulator last.that way no m oisture gets in the system. have your a/c/shop then vacuum and recharge with virgin refrigerant. should make your nipples as hard as rocks come summer!