1976 DeVille AC Conversion to R134

[P. Manoogian]

Having trouble with too much pressure in low side (70 lbs). I have already replaced the VIR with an Old Air Products Eliminator kit, replaced the compressor, flushed and blown out the lines, the evaporator and the condense. Will put in another A6 compressor tomorrow and use PAG oil instead of Ester oil.


Has anyone got any insight or experienced this on a conversion? Thanks

[fishnjim]

Confirm system was evacuated prior to filling and proper charge (lbs) was added.
I don't think oil will cause a pressure issue, but will affect the compressor life, if not the right one.

[P. Manoogian]

system was vacced down to -29.8. Slowly creeps up though... trying o fin a leak with injected dye and ultraviolet light - nothing yet.

[V63]

Did you replace the hoses?  I have had issue with Schrader valves so when I put the pressure switch in i removed the Schrader valve first. Also check the charge port Schrader valves for leaking. Do you know how many ounces of refrigeratant you have in the system? Soap bubbles work great for finding leaks. I had TERRIBLE lick getting a rebuilt A6 worth a crap...finally bought a new one but had to move it forward 1/2 inch  to align belts on a 76 .

[The Tassie Devil(le)]

I have been told that the R134a can leak through the R12 hoses, so the hoses should also be changed.

Bruce.

[TJ Hopland]

What did you use for a receiver dryer?  If it was one of the universal ones where the manifold swivels those won't hold vacuum.  Mine didn't hold vacuum very well but I was so frustrated I just charged it anyway.   It held for over 4 years before it needed a top off. 

Only thing that was original in my car under the hood is the evaporator and the systems works fine.   Got the eliminator, universal dryer, sanden  compressor, crossflow condenser, and new custom hoses.   

[cadlove]

I'm sorry to have to tell you this, but the GM A6 compressor is not designed to run on PAG oil?

This is not my opinion. It is an engineering fact.

I know loads of these conversions are done, the compressor will suffer premature wear, usually they get noisier and then fail. It's also known that on occasions the clutch bearings fail and/or leak, some blowing the front end right off into the fan. I know of this happening.

In the States you can get recycled R12?

The other option is RS24 (R426A) which is a perfect drop-in gas, working at the correct pressures. Sadly it is expensive. JP

[V63]

I had not heard that PAG oil was  at issue or is it the fact of mixing with existing non compatible mineral oil that was not removed?

On rebuilt A6 compressors I had quality control issues with those long before R134, they would be seized fresh in the box, could not turn them🤦🏻‍♂️. Junk. Finally, I did find a small private label that could rebuild them.

Fast forward today...bought 3 rebuilt A6 from local parts store and they would not turn at all...seized. These were national 'name' brands 🙄. All come precharged with 3 oz PAG. So I tried the new aluminum NEW A6, also charged with 3 oz PAG. Have tried 2 on them and so far so good.

The shop that did the last (Failed) A6 that was existing on the car placed a conversion label with mention they added '2 oz' of PAG🤪, so either they mixed it with mineral or they didn't add enough oil.
I am NOT using R134 nor R12 😉 however,  Working at lower pressures.

["Cadillac Kid" Greg Surfas 15364]

On the question of high low side pressure, until the system (if everything is working correctly) has "pumped down " to the point where the evaporator is at near 40 degrees your back pressure will be high.
Now the "VIR eliminator" contains, or at least should contain an expansion device such as an orifice plate calibrated to flow the refrigerant, a connection for the oil return and a pressure or temperature switch to cycle the compressor.
That said the A-6 was  NEVER meant to be cycled and doing so usually leads to a premature demise. What the VIR does as well is to eliminate liquid refrigerant from slugging back to the compressor and nocking out the compressors valves. 
If it seems that I am prejudice against eliminating the VIR and all its functions you are correct, and the use of R-134a reduces the capacity of an A-6 system by over 20% 
Greg Surfas

[Caddyholic]

 I am NOT using R134 nor R12 😉 however,  Working at lower pressures.
[/quote]


So what gas are you using?

[P. Manoogian]

I understand the desire to keep R12 and the OEM vir valve, however the owner of this car is seeking 50 - 60 degrees of cold air. Here is an outline of the facts:


1.) System was empty
2.) all or rings were replaced
3.) VIR was replaced with Old Air eliminator kit
4.) system flushed and blown out twice
5.) compressor replaced with Four Seasons rebuild
6.) Hoses inspected and pressure tested with compressed air - all good (42,000 mile car)
7.) Things were going fine with old VIR valve until pressure went sky high and seemed to wipe out clutch on first "rebuilt" compressor


Now awaiting replacement compressor which I will load with 8 ounces of PAG and put 1 ounce in condenser and 1 ounce in evaporator.
I will get a second vac pump and vac down as my old Robinair may be defective.


I guess I am hoping that too much low pressure was a result of a defective rebuilt A6...will know soon.
PS - Greg Surfacc, I respect your knowledge on these but sometimes people just want 2 or 3 years of "good" AC without blowing the bank. I have 20 hours in this already that I will eat, just want it right.

[V63]

I have lost all confidence in readily available 'rebuilt' A6 compressors. Especially the one you mentioned. The only season they blow cold air is the dead of Siberian winter 🤣. (Save yourself and Try to turn the replacement compressor fresh from the box with your hand).  If someone knows of a reputable source I might reconsider.
Until then I have been using those Brand new aluminum versions. Remember the System oil capacity is a specific volumn. With each compressor failure are they contaminating the system?
If the pressure went 'sky high' there is a restriction somewhere.

I agree the A6 May not have been designed to cycle... but GM 'cycled'  the same A6 in Cadillac 1977 and 1978 and we had one new. The System was outstanding performance and offered wonderful service for 100,000 miles we had it. Mineral oil was fine too but times change and we are kinda  'forced' to comply with what's available by supply or price.

[TJ Hopland]

The quality reputation and cost of the A6 was why I didn't go that route on mine.  I think I did my whole system with the new Sanden, hoses, and new condenser for the price of just the replacement A6 compressor. 

Do you have a brand or part number for this 'new aluminum' A6?   I don't recall that being an option back when I did mine.  I do seem to recall more recently seeing that someone is making a bolt in replacement for the A6.   It looked to me to be more of a Sanden or similar more modern compressor that they made custom brackets and a outlet manifold for so it would bolt in place of the A6.  Seemed like a reasonable option if you already had new hoses.   It wasn't cheap tho,  I can't find it now but I'm thinking it was like $900.   I'm sure the compressor part is only in the $200-300 range so all the money is in the brackets.  It looked to me like they removed the stock rear cover outlet of what ever base compressor they were using and made a new block that had the correct outlets for the A6.  I bet it wasn't a cheap part to machine plus they had to pay someone to bolt it on.

["Cadillac Kid" Greg Surfas 15364]

If the compressor has been rebuilt correctly it WILL be hard to turn over initially. That is why it is necessary to add the requisite amount of oil to the compressor THROUGH THE COMPRESSOR SUMP DRAIN PLUG on then with the compressor in an upright horizontal position (like it will be when installed) using the spinner that fits the clutch plate hub, rotate the compressor acouplof dozen revolution until the oil pump has circulated oil through out the moving parts and shaft seal. As you continue turning it it becomes freer.
If you do not do this initial free-up you have Avery good chance of a very short compressor life.
In regards to pressures, be sure and charge the system correctly with R-134a being at about 80% of the R-12 charge
Greg Surfas

[35-709]

https://www.autopartskart.com/sku/fs58096.html?partno=fs58096&utm_source=google&utm_medium=shopping&utm_campaign=pnum&prodid=fs580966628&gclid=Cj0KCQjwvaeJBhCvARIsABgTDM7Mpg3YKDK4_tQiNnHakoeQOakl_iNeg0D5bZ0-zdD7CchCoY_y9lkaAgNCEALw_wcB

This is probably what is being referred to as the "aluminum A-6".  It is called an S6, a Sanden compressor with a front and back added to fit where the A6 used to reside.  I used one on my '35's 472 and it works very well.  As you can see, the price is less than $300.  I did have to modify the front mount (and space the rear) somewhat to move the compressor forward for belt alignment, but I probably used the wrong model.  I am pretty sure they make a model specific for the 472/500 which would be a drop in.

[TJ Hopland]

That looks like what I remember seeing,  I remember the covered clutch in the front.   That one is much cheaper but like you said maybe there are different versions and the one I saw was already further modified. 

[The Tassie Devil(le)]

I am running the standard A6 Compressor in my '72, since 2008, and it has never given me trouble.

It was a new one and was installed when the R134a conversion was done.

Bruce.

[V63]

If the compressor has been rebuilt correctly it WILL be hard to turn over initially. That is why it is necessary to add the requisite amount of oil to the compressor THROUGH THE COMPRESSOR SUMP DRAIN PLUG on then with the compressor in an upright horizontal position (like it will be when installed) using the spinner that fits the clutch plate hub, rotate the compressor acouplof dozen revolution until the oil pump has circulated oil through out the moving parts and shaft seal. As you continue turning it it becomes freer.
If you do not do this initial free-up you have Avery good chance of a very short compressor life.
In regards to pressures, be sure and charge the system correctly with R-134a being at about 80% of the R-12 charge
Greg Surfas

Strange...new compressors do not have this issue? when I say rebuilts are SEIZED I do mean SEIZED right from the box! ...wouldn't it make sense , as a rebuilder,  to do the added step you describe vs all the returns and frustrations?

Notice FSM says nothing about that procedure As NECESSARY when replacing the compressor However I do believe it's a great practice in so much as the 'rebuilt'  compressor will reasonably turn.

[V63]

https://www.autopartskart.com/sku/fs58096.html?partno=fs58096&utm_source=google&utm_medium=shopping&utm_campaign=pnum&prodid=fs580966628&gclid=Cj0KCQjwvaeJBhCvARIsABgTDM7Mpg3YKDK4_tQiNnHakoeQOakl_iNeg0D5bZ0-zdD7CchCoY_y9lkaAgNCEALw_wcB

This is probably what is being referred to as the "aluminum A-6".  It is called an S6, a Sanden compressor with a front and back added to fit where the A6 used to reside.  I used one on my '35's 472 and it works very well.  As you can see, the price is less than $300.  I did have to modify the front mount (and space the rear) somewhat to move the compressor forward for belt alignment, but I probably used the wrong model.  I am pretty sure they make a model specific for the 472/500 which would be a drop in.

Yes! That is the beast🤣

[cadlove]

Interesting about the oil-adding process?

Checked my '77 manual and as you say it doesn't mention where on the compressor to add oil? I checked the 1970 manual, same text.

The last A6 I fitted, a GM rebuild, it was their instructions that told you to add the oil through the compressor inlet and to rotate the compressor (I think) 10 times in order to get the oil to the front and around the shaft and clutch seals. Historically I know people who do this warning that if you don't, the compressor will have a short life?

When I had mine done the a/c engineer I used agreed that was the right way.

Regarding those who have bought rebuilds that were either already seized or seized shortly thereafter, don't you take parts back to suppliers? Bentley in the UK sell the A6 new, roughly $1400? I'm trying to find out where they come from.

I know everyone hates facts, but the A6 compressor requires 525 mineral oil. Their lives will be much shorter with PAG oil.

Too often, as someone mentioned, people want either the easy option or the cheap option? I don't know why you don't pool your resources and someone take the EPA 609 exam so R12 can be used. Before using it replace all the O rings, lubricate the new ones with 525 mineral oil and vac the system several times. Vac it down, measure it, use the car a few weeks, check again. Then use R12. I wish I could.

Remember Cadillac's words to its workers - Craftsmanship a Creed - ACCURACY A LAW

JP