I added 3lbs of r-12 to my original 70. It hasn't seen service in at least 6 years-the AC that is. My buddy put gauges on it, the high side is not showing any pressure , the low side has a reading. After I added the 3 lbs, temp went to about 70 then turned hot in less than 2 mins. Think it has a clog or faulty valve? The sight glass is nearly clear. We tried a leak detector and there are no leaks in the lines anywhere. What do I try next? Looking to go to Super Chevy Friday in Pa. with this car.
Thank-you!
John

If there is no pressure on the high side I would suspect either the compressor or the number one problem the POA valve. The valve is outside the evap box in the engine comp on the upper side of the box. It senses pressure and adjusts the freon flow to the evap. They are almost impossible to find but they make a retro fit part called a POA tube replacement. It solves all the problems the original POA valve has and has an adjustable pressure switch built in. Hope this helps.
Mark

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72SS/402/T400
97 Chevy Tahoe/Whipple Supercharged 2002 Camaro SS

3lbs or 3 cans, the cans are 12oz and not a lb. You put 36oz in and if I remember correctly the system calls for about 60oz, so in fact if there was no pressure in the system and you have no leaks, you should have evacuated the system for at least an hour and installed the freon after and I think that those systems call for 3.75lbs.

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Leo Paugh
Maryland Chevelle Club #017
A.C.E.S.#3731
progress has little to do with speed, but lots to do with direction.
Maryland Chevelle Club (http://www.chevelles.net/mcc/mcc.htm)

Is there a way to test the compressor? Also , this guy didn't evacuate before putting in 3 lbs or 3 1/2 cans. Even if it had 3 1/2 cans it should be at least cool right? Are these valves expensive? Now I wpould have to evacuate the system to install right? You guys are the best!
John

John, I don't know where you live but in most states the freon has to be recovered by a qualified shop with the right equipment and then it can be recycled. This may be to your advantage if you chasing a problem and need to take the R-12 in and out.
The valves range from $70.00 to $120.00 depending on the supplier. Any A/C parts house can probably help you. If you need help finding one I can probably dig through my records to see where I purchased the last one. Let me know.
Mark

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72SS/402/T400
97 Chevy Tahoe/Whipple Supercharged 2002 Camaro SS

There is pressure on the high side, there has to be
Find the reason for no gauge reading such as hose not opening valve core

If the system wasn't evacuated, you probably just through the cost of the R 12 out the window because it is most likely contaminated now (unless of course it wasn't empty to begin with)

If it wasn't completely empty I think I would add more until the sight glass clears just to see what it does

Yes,
This guy did not evacuate first. I believe the system was empty. He said try adding R12. I had some left over from when it was cheap. So now I'm back to blowing hot air and 3 cans of R-12 I guess are useless. How can the compressor be checked? This could run into some $$ now I guess. For a car that rarely gets driven...hmmm..
I don't want to just replace parts and hope for the best! POA valve sounds reasonable-if it will cool again. It always seems if an A/C system has been monkeyed with, there is always a problem and you only get a season out of it. Any ideas?? I don't want to through $$out the window here. Sorry for the bad pun!!
John
Thanx for your help so far guys!

Sounds like the system is about half charged with a mixture of R-12 and air now which will cause high head pressure if more refrigerant is added

If you don't want to try adding more R-12 (which probably would be just throughing good refrigerant after bad)
Probably the best thing to do now is like Mark says, change the POA valve to the modern type, replace the drier, flush and
evacuate the system and recharge with R-134

The compressor can (sorta) be checked to see how good of a vacuum it will pull but first you have to get the gauges connected properly to get a proper reading.

With an empty system you could temporarily jumper the LPS and run the compressor for about a minute and see if it pulls down into a vacuum

If you really would rather leave it an R-12 system then I would dump the charge, check the compressor, change the filter-drier, evacuate and recharge the system with the proper amount of R-12 and about 4 OZ of refrigerant oil

or

you could take it to a professional and just tell him to make it cool good

I had the same problems and it was a bad POA valve and I got a new updated one from Old Air. I had problems again with my drier getting clogged because my condenser had some type of corrosion from tears of sitting. It ran great for 1 day though!I know need a condenser. Does anyone know where to get one for a good price?