Ok, there seems to be a lot of different views on this subject, but i'm hoping someone can give me a pointer or two in the right direction.
I have a nasty feeling that i might have a leak in what i would call the "heat exchanger" for want of a better term (sorry, not very clued up on A/C systems - England's too cold so most cars don't have it!) I mean the matrix that sits inside the heater box, where the inlet air flows and is cooled. When i shut off the engine after using the A/C, there is a gentle hissing, audible through the dash vents.

The big question is, if I do have a leak, and take the unit out to be fixed, what should i use to have the system recharged with? Its a 1980. Is the refrigerant this system was designed around still available? I appreciate that things may be different in the states, but I'd just like a few opinions. Will using the wrong refrigerant bugger any thing up?

Hey Theo,

I don't know what R-12 will cost you in the UK, but it has gotten expensive here in the US. The previous owner of my Vette had the system changed over to R-134a, the more enviromental friendly refrigerant. He was having a problem with the old system leaking freon and it was continually costing him big money so he had it converted. I do not think you can just put the new type of refrigerant in the old system. I have seen some articles on the net addressing the issues and what all is involved in doing a conversion. It used to be a very spendy proposition to get it done here but the prices semed to have dropped considerably in the last few years but with you being in the UK, no telling what it will run you. Best of luck! Let me know if you need any pics of anything under the hood of mine for you to check out. I am still totally stock for the most part and all the parts are still there if you need to see something.

CVT4ME

Theo,

Check this link for do it yourself tips. It is for an F-body but I am sure it would be the same on your Vette.

http://www.fbody.com/tech/details.cgi?id=15

Cheers,
CVT4ME

Are you sure you have a refrigerant leak? The vacuum doors closing can make a hissing sound as they lose vacuum. The matrix is called an Evaporator inside the car (actually just outside the firewall) and a Condensor in front of the radiator. There is still a lot of R12 refrigerant floating around in small cans on Ebay and other places. I have 2 30lb cylinders that I would like to sell sometime, no good for you, but my point is that R12 is still available. A few years back you could get a liscense to buy it by taking an open book test through the mail and paying around $20 through MACS, don't know if that is still an option in the states. There is a lot of stuff written on this and other websites about refrigerants. My 2 cents is stay R12 (preferred) or change to R134. If you convert an old system to R134 expect to change the compressor as the front seal will not last long in my experience. I would not use any blends or "substitutes"-period. The molecules are different sizes and when you get a leak the composition of the charge will not be the same. It is impossible to just add some blend to re-balance the charge. In summary, I would determine if I actually have a leak. If it was a hose, Evaporator, or Condensor I would repair it and recharge with R12. If it is the Compressor I would probably replace it and convert to R134. Good luck with it.

Howdy Theo
How long have you had this "HISSING" sound? If it is more than an hour or so it is most likely one of the vacuum diaphragms that open and close the doors in the heating & A/C system. One way to check would be to disconnect the vacuum supply line from the engine (engine off) and hook-up a vacuum pump (small hand held will do just fine). Pull a vacuum on the system and listen for the hissing sound. Or if the hand punp has a vacuum gauge, is if the system will hold a vacuum.

Cheers guys, for the responses. I must admit, given the different views I've seen, I was expecting my question to spark up a whole debate about what's best, but there seems to be a fairly constant message - keep with R12 if you can find/afford it! I have very little experience of aircon , since it was only the very top end motors that had it a few years ago. Certainly in 1980 it would have been in the realms of the Jags and Rollers. So i don't know how hard R12 is to come by in the UK.
As for the leak, you guys could have a point about the vacuum doors - i really hope this is the case! Only there was one other thing that made me concerned: When the A/C is running, it goes for less than a minute at a time, before the clutch pops out. Then it comes back in after a bit, then out again. I know there's a pressure switch, that is supposed to interrupt things to stop the compressor pumping in the event of pressure loss. So i put two and two together and wondered if the pressure's dropped because of a leak, and the clutch is popping out because the pressure switch is doing its job. By this rationale, then if i were to keep running the A/C, the clutch would "cycle", being held in for less and less time, until the pressure drops so much that the clutch would never be allowed to operate. Sounds a bit pessimistic, i know, but i'm soon taking it to an A/C guy who's worked for a long time in the states - this should sort things out. He'll no doubt have some views on the whole R12 debate!

As far as what type? I'm going to r134a.

I know so little about it, that i wouldn't even know if R134a is used as the R12 replacement over here. I imagine it probably is though. But like i say, i'm hoping a chat to this A/C guy, this weekend, will give me some pointers.
I just hope i don't have a leak in the first place....