car a/c quesion. Freon 12 conversion...

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I bought a nice low milage 1978 Lincon Town car a few years ago. At the time of the sale the previous owner told me that the air conditioner had been converted from R12 to R134. This year the a/C is not as cold and needs a recharge. How can I tell if it really has been converted? What happens if I add R12 to a converted system? What happens if I add R134 to a system that hasn't been converted? Thanks, Frank

posted by  bbaddog

Take It To A Mechanic And Check If They Know.

posted by

I thought that was what this board is for?

posted by  bbaddog

That's great response "Take it to a mechanic." I dont think you could tell, I do beleive you can use 134a in an R-12 sytem. The only way to be sure is to completely empty the system of whatever freon is in there. Also you'll want to change the sytem's oil. Some systems collect the oil at the bottom of the accumulator and return the oil directly to the compressor through a separate line. It is very important to use the correct oil with the correct freon
This may help you:

posted by  Pinstriper38

There is a direct replacement for R12 (eg R413a) now rather than R134a.
You can't just use 134a without changing bit 'n bobs, like expansion valves.

Make a call to a refrigeration parts wholesaler to find out what brands are available.

posted by  Wally

are you thinking of 414b (hot shot)? that is a drop in replacement for r12. and you should be able to use 134a in lieu of r12 if you use the appropriate oil (POE instead of the mineral oil that 12 uses) they sell conversion kits at parts stores that have the oil, refrigerant, instructions, and appropriate fittings...

posted by  dodger65

I merely quoted one of a myriad of direct replacements now available and no I was thinking about the number I posted. I haven't checked out 414b for evaporator temp compatility, but I suppose you have done that anyway? If you just change the oil and whack in 134a, start counting down the days until the compressor fails.

posted by  Wally

yeah, i've got hot shot in the red car in my sig--works great! what makes you say the compressor will fail?

posted by  dodger65

I use 134 in my 12 system and have for years with no problem. I didn't change anything.

posted by  Dave

The tolerences on older compressors do not allow for the increases in pressure required by R134. Doesn't it have something to do with the input shaft seal, wally? Anyway, in the states shops are required to place new stickers on systems converted to R134 and usually if the accumulator looks newer than the rest of the system it has probably been switched over. :2cents:

posted by  srober32

yes on some very older systems you would need to change alot of stuff to make it compliant.. but some just need to evacuate and change orings and new oil then charge with r134a

well the fittings and a label usually tells it.

posted by  thongsai

well, i asked my boss this morning (20+ years HVAC/R, MVAC) and he said that the only reason it would fail is if it was failing already or if it was not done properly. if you look at 134 and 12 in a p/t chart, they only differ by about 20 psig at the very outer limits of operating temps, so i vote that if the system isn't damaged already, a retrofit should serve most folks just fine (done properly) :2cents:

posted by  dodger65

Yes if it's not done properly it will probably fail. PT characteristics are not a singular guide to refrigerant compatability, ask your boss about the other properties that go into the selection criteria.

posted by  Wally

exactly what selection criteria are you talking about? (don't read this wrong, i'm just not clear on what you're asking)

as far as the p/t compatibility, i was referring to an earlier post that spoke of pressure differences between 12 & 134...

posted by  dodger65

I want to thank you all for the advice. I compared my car with one exactly like it and the fittings and everything else are exactly the same. The sticker on the compressor is the original r12 sticker. I don't think anything was ever changed. I just don't know why the seller would tell me it had been changed unless somebody charged him to convert it and then only recharged it with r12.


posted by  bbaddog

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