I am in the decision stage of the AC overhaul on a frame off 72 Hurst Project.

Status of the original system

Evaporator - seems to be in excellent condition will have it pressure tested and cleaned by local Radiator Shop (Rex Radiator)

POA - will have this restored (Classic Auto Air seems to be the top choice) open to other suggestions.

Compressor - will have this restored (Classic Auto Air seems to be the top choice) open to other suggestions.

Liquid Hose Line - will need to purchase a new one, previous house had a hose clamp on both ends.

Suction Hose - Looks to be in excellent shape will have it flushed and installed

Discharge Hose - Looks to be in excellent shape will have it flushed and installed. NOTE: have a question on how to test that the muffler is operating properly

Drier - will have this restored. Has anyone handled this themselves it seems very straight forward in cutting top off, cleaning internal unit replacing the desiccant material, reweld top on and paint. Please provide your thoughts on approach or better off letting the experts handle this.

Condenser - Looking to replace with new Parallel unit from Classic Auto Air


The other question is to run R12 or 134a - seems like folks are split on this topic.


Please let me know your thoughts on my approach and if you have any suggestions they will be greatly appreciated.

Located in Northern IL if any recommendations on local shops that can restore these items.

 

Don't run r134a. You will be disappointed in the AC's cooling capacity if you do. Either have a shop replace the r12 or consider an anti-EPA option like Freeze 12 or r12a.

I bought a r12a kit to recharge the AC in my Ford truck. It's supposed to work well. I actually plan on doing it this afternoon. Standby for an update.

 

I've converted several cars from R12 to R134. In most cases I did nothing special, just replaced the drier and orifice tube (and the compressor where needed), vacuumed the system, added the appropriate oil and freon, and they cool just fine. I'm in the mid-Atlantic, so 95 degrees and 95 percent humidity are common in the summer.

On a POA valve system, definitely have the valve recalibrated for 134 if you go that way.

 

I wonder how the radiator shop will "pressure tested" the coils. Usually a rad shop will submerse in water and check for leaks. Very bad for a refrigeration system. dry test with nitrogen is the correct method.
Mike

 

Any good source for a replacement A6 compressor?

 

I've just done this on my 71 convertible.....and my thought process was to replace everything and be done with it. Evaporator, hoses, TXV, condenser and compressor and a rebuilt POA valve (calibrated for R134a).

Everything came from CAA except the Pro6ten compressor.....which I got from Old Air Products ( I think)....I accumulated all the parts over a couple of years.

I digress, I was on the fence about R12 or R134a and ultimately went with R134a and so far am very pleased with how well it cools....and down here in Charleston, it gets pretty warm.

Cheers,

Troy

 

For a high-value car like a H-O, I would tend to lean toward using R12, as it makes the restoration that much more original.

As for the liquid line with hose clamps: Do the clamps have little "locating fingers" that just reach over the end of the hose? If so, they're probably original.

- Eric

 

Erique,


I have not seen any original liquid hoses on the 68-72 cars have the clamped on ends - only the crimped on kind.

 

Oh, okay. Some of the C-word cars used them in this period.

- Eric

 

The liquid line was a hack job no way it would have held pressure properly. I will be running R12 and look to keep most if not all original parts and either have them restored or find some that have been restored already. I am still looking for a A6 compressor as CAA wants $400 to restore the original which is a bit too pricey IMHO.

 

Has your compressor failed? If it hasn't, there isn't much to reseal it and install a new front seal. The biggest problem is finding the tools. When I took the first one apart, to replace the large O rings, I was surprised at how simple of a job it was. If you have to get into the actual mechanical guts of the compressor, that is a difficult and tedious job, that requires critical skills to do correctly. For this reason, if I open one up and find metal filings or other damage, then I just put it back together, and look for another. Removal and installation of the front clutch / pulley assembly is a breeze with the correct tools.

 

There was an A-6 compressor NOS on ebay yesterday. Price seemed OK. I paid $600.00 for new A-6 compressor 2 years ago.

 

Never mind e bay. Look in our parts section , someone has what you need, $350.00. I would jump on it.

 

The mounting bolt spacing on the A6 compressors isn't always the same. Have a friend that has a 1975 Cadillac, and his compressor was shot. He had a 1974 Cadillac parts car, and he took the compressor off of that and tried to put it onto his car. Wouldn't fit... it was off just enough that the bolts wouldn't line up. He then took all the mounting brackets off the 1974, and put them on his 1975. When he was taking them off, they looked identical to his 1975, and the 1974 brackets fit the engine block fine. I don't think that the problem was Metric vs. USS/SAE, but a change in manufacturing dimension. I personally haven't run into this problem, but it is something to think about when purchasing replacement parts. Just because they look alike, there may be slight differences that you are not aware of.

 

Also, if you are looking to get it exactly right, watch the "clocking" of your clutch electro magnet. The terminals should be pointing to the 10:30 position if you are looking at it from the front of the car. Most reman. compressors with the clutch already mounted are usually clocked at 1:30 - it will work, but the wire harness will be stretching to reach it.

 

Hi Joe,

I´m very interested on these threads dealing about R134a conversion, as my 70 Cutlass now is strongly needing a recharge -last time it was recharged with R12 was 2005- but in Spain, where I live, it´s extremely difficult finding R12. It´s definitely banned nearly 10 years ago (Exactly 1998 but in 2006 it was still easy to get it, as there was a transition period) and who sells it will have to pay a big fine and put at risk his authorization as a refrigeration dealer if he is discovered... So in my case the best option is doing the conversion -though R134a is not as efficient as R12 in this system- but I want to follow this route helped by a refrigeration technician I know, who has asked me about the peculiarities of these cars compared with more modern cars he is used to... I hope that following your advice my car´s A/C will work fairly well (though not as good as with R12; I assume that) because right now the performance is very low and I´m afraid I could damage the compressor runnig it with a too low level of gas.

I understand the rest of the conversion but I have one doubt: Where is the orifice tube located on this car... How can I get it changed and which one should I get to replace the original? (specifications)

Thank you in advance... Here is the presentation thread of my car: https://classicoldsmobile.com/forums...k-hardtop.html

I have done several fixings I will comment on the threads I opened to ask about

 

There is no orifice tube.

Your car has a variable orifice, called an expansion valve, which operates in conjunction with the POA valve to maintain a constant and correct flow of refrigerant from the liquid line into the evaporator.
The system is designed to run constantly, with the flow of refrigerant modulated to account for temperature, humidity, and engine speed, which is different from modern systems, which turn on and off in order to modulate the refrigerant flow (sort of an analogue vs digital concept).

If your refrigeration friend is not familiar with this sort of system, he should read up on it before messing with it.

- Eric

 

Thank you Eric... I´m no expert on A/C. I´m learning little by little by solving problems... In my Dodge we did the R134a conversion one month ago, just changing oil, rubber tubes, dryer bottle and compressor o-rings. It was a 1973 aftermarket very simple system: No expansion valve, no POA valve... Just like a fridge and the results are good so far. Air temp from the vents was 6ºC=43ºF. In my 69 caddy I was lucky to find the last R12 charge I could find 4 years ago and it´s still working. No conversion needed: I got installed a new compressor from rockauto, as original one was nearly seizing up, new dryer bottle and expansion valve, a good system cleaning (specially the condenser) and it cools the car very well even when it´s parked for hours under the sun at 98ºF.

Then, should I change the expansion valve before using R134a... One with other specifications or just a new one designed for this car... from Rockauto, for example?

Which reading do you suggest about this system?... I have the shop manual so he could read the A/C part (I cand help him with translation)... Maybe a more specific document about R134a conversion on this system?

 

Expansion valves are the same for R-12 and R-134 - they open more if the output from the evaporator isn't cold enough, and close more if it is too cold.
They are not expensive, but if yours is working, there is no reason to replace it.


The Chassis Service Manual contains an excellent description of the function of the A/C system, so that is what I would recommend.
I do not know of a specific guide that addresses R-134 conversions, and is accurate, but I'm sure there is one out there.

Essentially, you should flush the old oil out of the system, replace the receiver/dryer with one that contains desiccant designed for R-134 (some companies will cut open your original, replace the desiccant, and re-weld it, if you want complete originality), replace the serpentine-flow condenser with a full-flow condenser, replace seals and hoses (the old hoses will probably work okay, though), and recalibrate the POA valve (there is an excellent post on this board about that), and it should work fine.

Good luck!

- Eric

 

Thank you again for solving my doubt and for your advice, Eric. I was talking with my friend yesterday about this topic and all what has been told here. Considering all this, He agrees that POA valve adjustment is part of the key for success in the conversion. We will do it and let you know the results.

We´ll use the Service Manual as our reference book and yes, I have seen detailed threads about R12 to R134a conversions these days. I hope all this combined with his theoretical knowledge and experience about refrigeration systems will help us.

Thanks also to all who shared his knowledge and experience in this thread.

 

You're welcome.

Please let us know the results when you are finished.

- Eric

 

As a more cost effective alternative, Benny Sanchez at Factory Auto Air also does A/C restoration and has done a wonderful job for me

 

Hi there!

Sorry for my late reply but until last sunday the work was not completely finished so I didn´t want to write an incomplete result...
Back in August my friend changed the dehydrator bottle and flushed all R-12 and old oil, recalibrated POA valve as recommended and filled system with R-134 and R-134 compatible oil. Same amount of oil and approx. 20% less of R-134 than R-12 original amount of gas according to shop manual... That was the idea but he run out of gas and the system was filled with 120-250 gr. less than optimum. We did not change by the moment condenser as we wanted to test how R134 worked in the car with original system. Nevertheless, the air from the vents was fairly cool. The first test was made in a friend´s shop, where we did the work, and it seemed ok though we did not test exact temperature. That day outside temperature was 37ºC - 98,6ºF and when the car was driven in urban circuit the air was not very cool with that temp but in road traffic the air was cool enough to provide a pleasant driving. As I got installed a temperature gauge, I noticed the engine temp with A/C on in urban circuit increased up to 100ºC - 212ºF so at that moment I shut off A/C. I checked then fan clutch and it must be toast as with engine off and hot I could move vent easily with my hand... So I ordered a new clutch that I´m still awaiting. If engine radiator temperature increase up to that point it must affect condenser performance as I later observed, so we must fix this before reaching a final conclusion.

Last sunday my friend completed charge of gas and tested air vents temperature: 6,5ºC - 43,7ºF. The day was warm, 26-27ºC - 79-80,5ºF, but not hot. We did a road test measuring temperature. In urban traffic engine temperature rised 5-10ºC - From 176 to 194ºF and that was the increase approx. in air vents with max. cooling (measuring in Celsius; not valid for Fahrenheit) ... In the worst situation the air temperature was 15,5ºC - 60ºF... I hope this results improve when the fan clutch is changed, as radiator temp is closely related to air from evaporator temp.

My friend observed that temperature oscilation and therefore pressure oscilation was very steady, unlike many modern cars A/C systems he had seen, surely thanks to our friend, the POA Valve. That´s a great help for the system, avoiding compressor wearing and damage in other components.

I would like to test again the system with fan clutch changed, especially in urban traffic but unfortunately temperatures are going down and conditions would not be the same... I will have to wait to the next summer to remove all doubts... But I did not want to wait a whole year to post my update


Thank you all for your help... What seems certain is that I can drive the car in the road with high temperatures with windows up, silent and comfortably.