I decided to try to get an early start on the AC in my 74 Vette. I bought this in early October of last year with the AC not working. The unit seems to be complete with no apparent leaks. Everything looks dry, no signs of wet hoses or seals. The system has no pressure in it at all. The car only has 26,000 miles so there shouldn't have been any compressor problems at that mileage. Now I know that doesn't mean anything for sure, but I am trying to be positive! Yesterday I hooked up the AC gages and vacuum pump and pulled the system down to a 28 Lb vacuum, closed the gage valves and the system did not leak down, even over night so today I ran the pump for 3 hours to draw anything out from in the system. Now the question I have is, should I change the system over to R134 or use R12? I hate to use R12 and find out that the system doesn't work. If I go with R134 and the system works would you keep it converted or vacuum it out and go back with R12? With the interior being so small as a 2 seated car I am sure that R134 would be cool enough if the system functions. If the system doesnt function then there will be other things to consider. I'm not even sure I really have a need for the AC to work but it would be nice if it did! What do you think?

Many people say that the R12 gets colder but I converted mine to R134 last summer under the expert guidance of Kyster, our resident expert at C3VR, and got excellent results. Now don't be fooled by the small cabin. These things generate a lot of heat from the engine bay, the heater core, and the exhaust. You can somewhat cure all of these heat sources. You need to ensure there are no openings in the firewall, insulate the floor under the carpet, and put shutoff valves in both heater hoses. These things alone knock down a lot of heat in the cabin. Sounds like you are well on your way. My advice is to convert to the R134. Hope this helps.

Scott

I agree with Scott...go for the full conversion to 134a, and insulate everything.

Pull all that crap out and save 300 lbs!!!

If ya want comfort, buy a C6!

I got the clearance from the wife to pull all the AC stuff out of ours.  I'll keep it, of course, but out it comes if it ever comes back from paint!

UPDATE:
I charged the system tonight with R134. I only used 36 Oz of freon as I have read to only use 75% R134 of the required R12 original application. Compressor runs quiet as can be. Vents all seem to work. I guess the real test will be once the temps start going up outside which looks to be a while. I feel good knowing that is completed and I can move on to something else now. Next will either be an exterior detail or a motor detail. Not sure what I want to attack next. 

Sound good. Even if you don't need it, run it occasionally to keep everything lubricated. If you don't, o-rings and seals will begin to shrink and the refrigerant will slowly escape. Preventive maintenance is the key.


Scott

Did you charge it without changing the oil in the system? 134 don't mix too well with the old type(R12) oil...if it don't mix, it don't carry the lubrication to all of the parts that need it. You need a different type oil in it for use with 134.
There are two kinds of oil you can use with R-134a. Ester oil will work fine mixed with a small amount of the mineral oil used with R-12. The other kind, PAG oil, will get contaminated with mineral oil and won't lubricate the system properly. Some say it also requires special seals, cause it'll make the old seals "wear out quickly"....don't know if I agree with that, tho.

There are A/C folks here that can give more info on this...Adams' Apple2007-04-12 19:20:58

[QUOTE=ranger3]Sound good. Even if you don't need it, run it occasionally to keep everything lubricated. If you don't, o-rings and seals will begin to shrink and the refrigerant will slowly escape. Preventive maintenance is the key. Scott [/QUOTE]

I had mine converted to 134a and it is plenty cold in the summer.

Well, here's my 2 cents from an A/C tech. I have retrofitted to 134a many of the cars I've worked on mainly when compressor, accumulator, etc. is replaced. However on the other hand I have charged just as many with R12. The real advantage of using 134 is the cost and availability. I have not had a problem at this point buying r12, and the price has gone done some as of late. I am in the business of fixing a/c systems, so I feel if the car is designed to use r12 then thats my first choice. If the system is tight who care whats in it. I have really not seen a drastic difference in duct temp. between the two. Because of cost I do recommend retrofitting cars that need to be charged once a year or so when the customer declines costly repair. Now as Joel stated. The most important thing is to get the proper oil in the system. I have used ester oil when just changing over to 134, but when components are replaced I use the vis. pag oil that the system requires. Pag oil does not travel with mineral oil, but from what I've learned a small amount of mineral oil in the system won't hurt. As far as orings and seals, yes the newer ones are made of neoprene. But my feelings are if the orings are not leaking don't worry about it. The only way the oil will get at the rings is through a leak. Well, Its more than 2 cents worth and I'm sure you all are as throughly confused as I am. Let me know if I can help. Terry