'78 Air Condition pressures for 134a
Thread Starter
Racer
Joined: Feb 2002
Posts: 269
Likes: 0
St. Jude Contributor
'78 Air Condition pressures for 134a
Okay, after flushing, changing accumulator, new oil-dipped o-rings, fixing leak, vacuumed down to -30" for 1 hr and and charged 2 cans of 134a upside down, then 8oz of oil upside down, then hooked up the 3rd can or 134a and left right side up.
Pressures are now 290 high, 60 low while compressor is on. 90 degrees outside.
Feels like most of the 3rd can is still in there.
First question: Is it normal for both sides to settle at 110psi when the compressor is off?
Second question: It doesn't feel quite as cold as it should be... My service manual says it takes 3 lbs of R-12. 85% of that is about 2.5 lbs... which is about three 12oz. cans.
Can you tell me what the pressures should be for optimal cooling?
Did I put too much? If I put too little, how do I get the rest of the can in? I let it sit for about 20-30 min while slightly revving up the engine.
Thanks.
Marc
:smash:
Pressures are now 290 high, 60 low while compressor is on. 90 degrees outside.
Feels like most of the 3rd can is still in there.
First question: Is it normal for both sides to settle at 110psi when the compressor is off?
Second question: It doesn't feel quite as cold as it should be... My service manual says it takes 3 lbs of R-12. 85% of that is about 2.5 lbs... which is about three 12oz. cans.
Can you tell me what the pressures should be for optimal cooling?
Did I put too much? If I put too little, how do I get the rest of the can in? I let it sit for about 20-30 min while slightly revving up the engine.
Thanks.
Marc
:smash:
Le Mans Master
Joined: Sep 2000
Posts: 5,635
Likes: 4
From: Orlando Floriduh
Re: '78 Air Condition pressures for 134a (Marc78)
That is OVERCHARGED.... You want 26-28 on the low side with the engine running at approx.2000 rpm. It takes less R134a AND it is much more sensitive the the exact right amount. Once you find that "sweet" spot, R134a works very good. When you shut the car off, the system "equallizes" and the pressure throughout the system becomes whatever the pressure of R134a should be at a given temp. There are charts for this. Mine works best with only two cans of R134a. A friend of mine's GP also works great with two cans.
[Modified by silvervetteman, 5:31 AM 7/8/2002]
[Modified by silvervetteman, 5:31 AM 7/8/2002]
Thread Starter
Racer
Joined: Feb 2002
Posts: 269
Likes: 0
St. Jude Contributor
Re: '78 Air Condition pressures for 134a (silvervetteman)
How can it be overcharged when I started from empty, and the svc manual says it takes 3 lbs of R-12?
85% of 3lbs = 2.55 lbs
Three 12oz cans of 134a = 36 oz = 2.25 lbs + oil charge???
Is it possible that the compressor isn't doing it's job?
Come to think of it, when I felt the air at 2 cans + oil, it felt colder than it did now... but how can that be?
85% of 3lbs = 2.55 lbs
Three 12oz cans of 134a = 36 oz = 2.25 lbs + oil charge???
Is it possible that the compressor isn't doing it's job?
Come to think of it, when I felt the air at 2 cans + oil, it felt colder than it did now... but how can that be?
Race Director
Joined: Sep 1999
Posts: 11,361
Likes: 383
From: Plano TX
Re: '78 Air Condition pressures for 134a (Marc78)
The 85% figure is just an approximation. It's not correct for our cars. When I converted my '71 it worked the best with only 69% of the R12 charge.
The previous posters are correct. Low side should be in the mid 20's. High side no more than 250.
The previous posters are correct. Low side should be in the mid 20's. High side no more than 250.
Thread Starter
Racer
Joined: Feb 2002
Posts: 269
Likes: 0
St. Jude Contributor
Re: '78 Air Condition pressures for 134a (zwede)
Okay, I'll go with that. Thanks guys.
Zwede, I've been hitting your website many times to see your conversion.
Great site! (Although, some of it doesn't apply to me! ) :)
Zwede, I've been hitting your website many times to see your conversion.
Great site! (Although, some of it doesn't apply to me! ) :)
Thread Starter
Racer
Joined: Feb 2002
Posts: 269
Likes: 0
St. Jude Contributor
Re: '78 Air Condition pressures for 134a (Marc78)
By the way, could I have damaged anything having the pressure that high?
My system had been vacant for god know how long, and when I started charging, the compressor was squealing something fierce, but eventually calmed down and only squeaks every now and then.
I'm going to try to tighten the belt before I go any further.
My system had been vacant for god know how long, and when I started charging, the compressor was squealing something fierce, but eventually calmed down and only squeaks every now and then.
I'm going to try to tighten the belt before I go any further.
Team Owner
Joined: Sep 2000
Posts: 65,981
Likes: 15
Re: '78 Air Condition pressures for 134a (Marc78)
The squealing was your compressor not turning. You may have gotten some liquid refrigerant into the compressor when you added it with the can upside down. The compressor may be damaged. I think that anytime you hear that squealing you must immediately shut off the flow from the can and let the compressor clear itself asap. As you probably already know, a liquid is not as compressible as a gas and will ruin a compressor.
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Thread Starter
Racer
Joined: Feb 2002
Posts: 269
Likes: 0
St. Jude Contributor
Re: '78 Air Condition pressures for 134a (virtue4u)
You know, you're probably right. And what makes me really mad is that the instructions I got with my conversion kit said since the system was empty, to add the first two cans upside-down into the low side with the engine running and A/C on MAX.......
Now that its too late, I'm finding out I wasn't supposed to do that...
wth!?!?!?!
Why would the instructions say to do that?
:mad :mad :mad :mad
Now that its too late, I'm finding out I wasn't supposed to do that...
wth!?!?!?!
Why would the instructions say to do that?
:mad :mad :mad :mad
Team Owner
Joined: Sep 2000
Posts: 65,981
Likes: 15
Re: '78 Air Condition pressures for 134a (Marc78)
Nevertheless, try bleeding out some of that refrigerant. If you are lucky, the compressor is fine and you are simply overcharged. Maybe it will work better once you bleed off the refrigerant a little. Keep me up to date on your progress. Thanks.
Thread Starter
Racer
Joined: Feb 2002
Posts: 269
Likes: 0
St. Jude Contributor
Re: '78 Air Condition pressures for 134a (virtue4u)
Ok, I bled some pressure out last night, so that at 2000 RPMs, its a little above 30 on the low side. It started blowing cold, but the battery was out on my digital thermometer. Getting a battery today, and will slowly vent until the temp starts going back up.
Luckily, the compressor didn't squeak once.... it had been sitting idle for god know how many years without any oil, so I'm pretty lucky it sprang back to life with some new oil.
Will post results and temps tonight.
Luckily, the compressor didn't squeak once.... it had been sitting idle for god know how many years without any oil, so I'm pretty lucky it sprang back to life with some new oil.
Will post results and temps tonight.
