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1978 Cadillac Coupe DeVille
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Discussion Starter #1
Hi. I have a 1978 Cadillac Coupe DeVille with a converted A/C system. It was converted to R134-a a long time ago. I took the vehicle in today to possibly get it recharged and the guy was saying that it was never really meant for R134-a and technically the car would work with it but not that good. I asked him if R12 could be put in it even though it has been converted and he said yes it will work better with R12 as that is what the system was designed for. I need to know how many cans of R12 and R12 oil charge I need to recharge the system from fully empty. All the cans are in ounces so most of the cans are 12 or 10 ounce. And how much cans of oil I need, all the oil cans come in 4 ounces. The guy said that it should take 8 ounces of oil (two cans) and 3 cans of R12.

Thanks
 

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1980 FBC
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3,167 Posts
Your repair guy is correct. R-12 hardware does not play well with R-134A. Most of the problem is with the condensor.

On the internet you can always find someone who gets 2 million miles out of a Chevy Vega 4 cylinder and a conversion that works great.
 

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1926 Model T street rod, 2000 Jaguar XJ8, 1999 Corvette.
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6,738 Posts
Under the hood there should be a decal listing the r12 capacity. Radiator support or HVAC box on the firewall.
 

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1978 Cadillac Coupe DeVille
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Discussion Starter #4
I don't see any sticker

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so was my mechanic correct in saying that the conversion will work with R12?
 

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1980 FBC
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I should remember this.

It's either 3.25 or 3.75 lbs of R-12.

Was oil removed when the conversion was originally done? This includes component changes which remove some oil when R&Red.

You may not need any oil added.

Many conversions just add some oil.
 

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1983 FWB (Mac), 1981 SDV (Junkyard Dog)
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734 Posts
To return to R12 in the A/C system, won't all the residual R134 have to be vacuumed out of it? And wouldn't it be a good idea to check the orifice tube as well? My hi-miler Junkyard Dog 81 SDV showed minute particles of steel (attributed to wearing compressor bearings) in the orifice tube which was installed at the time of its last charge in 2007. I've got to get a reman compressor and have the system well cleaned and refilled with R12 or an equivalent other than 134 because I want to be able to freeze fish in the front seat when it is all done.

Cheers...........R.
 

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1980 FBC
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Good point.

Yes, on your vehicle the orifice tube should be replaced as it has a screen which gets clogged with compressor innards. The 1978 in question has a compressor that can last a long while before puking its guts.

Not knowing the service history of the '78 its hard to say the orifice tube needs replacement.

The 134A would of course have to be recovered and a high vacuum put on the system as part of the service.
 

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1926 Model T street rod, 2000 Jaguar XJ8, 1999 Corvette.
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Most retail rebuilders require you to replace both the dryer and orifice to enable any warranty on the compressor.
 

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1983 FWB (Mac), 1981 SDV (Junkyard Dog)
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734 Posts
I can understand a compressor rebuilder wanting to be assured that his product won't be adversely affected by pre-existing defects in the system but to specify that I replace my dryer to me is out of order. I want my engine room to retain its original appearance and for that reason I refuse to put on an aftermarket receiver/dryer with the octagonal top. Therefore I have to find a way to have my original dryer bone dry before I re install it. It should be doable. And I should still be able to freeze fish in the front seat (the hallmark of a good A/C system) with the finished product.
I think that we may have confused poor desi123 beyond reason. I (and the many others like me are anal to the extreme) must have all things looking and working like new. A tall order to be sure and one that drives wives to distraction. Not unlike the members who insist on cleaning their gennie wire caps in the family dishwasher.

Cheers.......R.
 

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1926 Model T street rod, 2000 Jaguar XJ8, 1999 Corvette.
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Do as you wish! The dryer is the in line filter. I can appreciate retaining originality but you also say it must be at its maximum coldness. Most systems depending on ambient humidity, wont get below 40 degrees in most cases. Fish will spoil eventually at 40 degrees. :) You might try finding a NOS dryer. They were shared on many E body GM cars. Maybe others as well.
 

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1983 FWB (Mac), 1981 SDV (Junkyard Dog)
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I guess i might have to get sensible and rely on Safeway for the fish. As I recall our new 81 Cutlass wagon had a dryer that was similar in appearance to the Cadillac dryer. I will check with my local GM dealer for a call to GM Vintage parts and see what they can come up with.

Cheers...........R.
 

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1978 Cadillac Coupe DeVille
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Discussion Starter #12
The compressor in the caddy is an A6 and I don't know what else would need to be done to put r12 in it and get it working. Do I have to change some parts and what are the right parts for r12 I don't want to go and buy a part that is direct fit and find out its direct fit for r134a.
 

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1990 Brougham, 1990 Brougham d'elgance 1979 Coupe
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The problem with 134 is if it gets low it doesn't work, even .5lb low. So to spend several hundred dollars on a 8$ problem might not be worth while.
 
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