How can you spot a r134 AC conversion?

[WyattTX]

It's time to recharge my AC in my '85 Silverado. But I don't know if a previous owner converted the AC system or kept it all the same. The parts look awfully fresh, so I'm a little worried. I think it still might be an r12 system, but I don't wont to risk tearing something up. Thanks.

[LeesTruk]

Usually a r134 conversion that's done by a shop, will have put a sticker somewhere saying so. If not, look and see if the hi and low side charging points have an adapter put on them. r12 and r134 use two different sized fittings (the r134 being the larger). Also, r134 gauge fittings are a two step mounting procedure, lift collar to install the fitting, then turn the valve head to create an air tight seal

[WyattTX]

Thanks, I'll take a look when I get home. Here's a picture. Can anyone tell what it is just by looking at it?

[LeesTruk]

On the receiver/drier, check the black cap. That's your low side, or suction side. If you take that cap off, is there another fitting/adapter screwed onto an existing fitting? Same for the steel line going into the evap. box? That's your a/c high side fitting

[Dead Parrot]

Here are closeups of OEM R-12 low and high pressure ports. Didn't take the cap off after spotting the Teflon tape sticking out. Don't remember why I used it but since the system is still cooling many years after being filled, decided not to risk it.

The one with the tape is the low pressure side on the dryer. The blurry thing in the 2nd pic is the high pressure cutoff switch.

[WyattTX]

It appears my dryer has a r134 fitting, and the cut off switch has a r12 fitting. Should I make the two match, or can I recharge as is? Thanks for the help so far.

[Ziegelsteinfaust]

The the fitting should be different, as the gauges use the quick disconnect, and the sensor needs the thread on.

The compressor will have a model serial that I would run to verify refrigerant. I do commercial ac, and we use the same driers for every refrigerant. I have some equipment that uses R134A, and use the same driers as R22+R410A. So a swapped in port would be normal for a shop. It ideal, but it works just fine. Plus a shop would have both types of hose's for their gauges.

The compressor is the only true way to determine refrigerant. As if you put the wrong refrigerant in it won't be at it's normal PT relationship, and stuff won't work right.

[kipps]

Originally Posted by Ziegelsteinfaust

....The compressor is the only true way to determine refrigerant. As if you put the wrong refrigerant in it won't be at it's normal PT relationship, and stuff won't work right.

Have to disagree on this one. The charts for R12 and R134a track very close together. They should perform similar. The sticker is the oil. The oil used in a R12 system is not compatible with R134a.

In industrial equipment, it's very doable to empty the R12 system completely of all refrigerant and oil, and recharge with R134a and a compatible oil. Obviously a new filter/drier, but the compressor, evaporator, condenser, and expansion valve would all remain the same.

[Dead Parrot]

Not an expert. I have read many threads on this forum on doing the conversion as I expected my system to fail years ago. The compressor developed a whirring noise shortly after installation. But the value of the R-12 used to fill it was more then the price on the compressor. Thing has been cooling and whirring for well over a decade. I even have a conversion kit I purchased at an end of season sale. Probably now qualifies as NOS.

Some constants in the conversion threads was flush and change the old oil, that R-134a is a lot less tolerant of air in the system, and R-134a also less tolerant about the charge amount compared to R-12(IIRC - you need LESS R-134a then R-12 for the same system.)

A gauge on the high pressure side would let you monitor the pressures as you fill via the low pressure port. Possible who ever filled the system used a R-12 high gauge and just knew the proper numbers. Also possible they guessed and it never cooled properly.

[WyattTX]

What is the OEM r12 charge? How much should I lower the charge for r134? What fluid should I run in the system, since I can't use linseed oil.

[hatzie]

The R134 charge is determined by pressures and temperatures in the system.
This post is a method that has always worked for me to get a decent even charge that cools without excessive head pressure on the compressor. If you use a scale you can note the weight of 134a required to fill the system.
http://67-72chevytrucks.com/vboard/s...48&postcount=6

R12 uses mineral refrigerant oil.

R134a uses PAG and Ester refrigerant oil.

[WyattTX]

Thanks, I'll try that. I apologize for mistakenly saying linseed oil earlier. I hope I don't cause someone to dump that in their system in the future. .