'81 Air Conditioning Question
Thread Starter
Melting Slicks
Joined: Mar 2006
Posts: 2,465
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From: Orange Park Fl
'81 Air Conditioning Question
I converted my AC to 134a a few years ago and it was never very cold. Now it has quit working altogether (I think it leaked down). I'm planning to replace the orifice tube with a VOV, vacuum it down, find and fix any leak(s) and recharge it. My question is, How much refrigerant should I put in and what should the pressure readings be once charged? Thanks and God bless, Sensei
Racer
Joined: May 2007
Posts: 285
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From: Ga.
I have an 82. I just got through replacing the compressor, Accumulator, and orifice tube. Converted to R134A.
With the R134A, it takes 80% of the R12. The Original R12 took 2.75 lbs., and 8oz of oil if completly dry. R134A has smaller molecules, so it leaks easier. The pressures should be around 27 to 32 on the low side, and 2 to 2.5 x ambient temp on the high side.
Hope this helps!
With the R134A, it takes 80% of the R12. The Original R12 took 2.75 lbs., and 8oz of oil if completly dry. R134A has smaller molecules, so it leaks easier. The pressures should be around 27 to 32 on the low side, and 2 to 2.5 x ambient temp on the high side.
Hope this helps!
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
1500rpm, blower on max, doors open
Slow down when you get to around 30 on the suction side, then let it run for around 20 minutes to stabilize and then very slowly add 134a until the temps at the evaporator inlet and outlet are ideally equal or within a couple degrees of each other.
The line to the compressor should be wet but not to the point of very, very cold.
Pressures vary too much with ambient temps.
Slow down when you get to around 30 on the suction side, then let it run for around 20 minutes to stabilize and then very slowly add 134a until the temps at the evaporator inlet and outlet are ideally equal or within a couple degrees of each other.
The line to the compressor should be wet but not to the point of very, very cold.
Pressures vary too much with ambient temps.
Thread Starter
Melting Slicks
Joined: Mar 2006
Posts: 2,465
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From: Orange Park Fl
Okay, so I started looking at the system this morning. My compressor is indeed cycling, so I don't think the refrigerant leaked out as I had supposed. I hooked up the test manifold, started the engine and set everything on "high". I got 20-40 lb on the low side as the compressor constantly cycled on and off (every few seconds), but had nothing on the high side. I thought my guage may have been bad, but I felt the HP line and below the orfice tube it is cold, above (where the HP fitting is), it is not. The vents do not blow cold. This sounds like a clogged orifice tube, right? God bless, Sensei
Race Director
Joined: Sep 2001
Posts: 10,560
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From: Wellington, FL
St. Jude Donor '11 thru '25
Any serious restriction in the system general results in a visible freeze point just after such restriction. If you don't see this, it's doubtful you have a restriction. With the compressor running, depress the hi side service port valve and see if pressure/refrigerant is released. If so, suspect a bad hi side connection or gauge. Your compressor is not running enough to produce cold air and 20 lbs is too low of a charge. Without being there, is hard to tell, but I suspect you are just low on refrigerant. 
Thread Starter
Melting Slicks
Joined: Mar 2006
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From: Orange Park Fl
Maybe I can make it clearer. The compressor cuts on and the pressure quickly (about 2 seconds) rises to 40lbs, then the compressor cuts off and the pressure drops to around 20lbs (again, in about 2 seconds), at which point it cycles back on, etc. If I try to add refrigerant, it does not take it.
The HP line at the orifice tube was quite cold, but I probably did not leave it running long enough to freeze. Thanks, Sensei
Last edited by a1sensei; May 8, 2008 at 10:50 AM.
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Drifting
Joined: Jun 2005
Posts: 1,523
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From: grand prairie texas
It sounds to me like the compressor is going bad. With the A/c and engine shut off are you reading anything on the high side? Pressures should be equalized low and high side with the system shut down. Should be around 120 PSI if I remember correctly.
Race Director
Joined: Mar 2006
Posts: 14,112
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From: Florida
There comes a point where you can't add refrigerant unless you evacuate the system completely.
Your present symptoms show a low charge.
Suck a very good vacuum, test for leaks and refill.
While it's empty, it is a good idea to replace the oriface tube for a couple bucks, since it contains a filter screen anyway.
Your present symptoms show a low charge.
Suck a very good vacuum, test for leaks and refill.
While it's empty, it is a good idea to replace the oriface tube for a couple bucks, since it contains a filter screen anyway.
Thread Starter
Melting Slicks
Joined: Mar 2006
Posts: 2,465
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From: Orange Park Fl
That's my plan. I hope to get to it tomorrow. By the way, it seems my HP guage on my test manifold IS bad. I guess I'll be picking up another guage set tomorrow too. God bless, Sensei
