Changing r12 to r134a

I want to convert my motorhome’s a/c from r12 to r134a . Do I have to change the compressor oil and replace o-rings , drier , txv valve ,etc. Or can I get away with just using one of these new blended refrigerants you see at the autoparts stores

You have to sweep the system components to remove any minerial oil, change the drier, add ester oil to the compressor and individual components, pull a vacuum to remove any air and moisture from the system, and recharge it with R134a.

And after you do all that, the system might not perform as well as it did with R12.


Tester is right. However I did it to one of our cars and everything went fine and still is some years later now. We did not notice any change in function.

Don’t try to cheap out with the stuff from the auto parts store, have it done properly.

Don’t try to cheap out with the stuff from the auto parts store, have it done properly.

Agreed. Have the job performed by an air conditioning technician. It isn’t a DIY type job.

Are you converting because it doesn’t work any longer, or are you converting because you want the new safe freon gas to save the environment?
Either way, you should call a commercial refrigeration repair man… There ia a new drop in replacement called “Hot Shot” R414B refrigerant. A blend which is recognized as non ozone depleting.
Originally developed for automotive use, it is now widely used as a drop in replacement for R-12 in commercial refrigeration.
If you use R414B Hot Shot, you will not have to change the oil from Alkyl- Benzene, to Mineral oil , or Poly_ol Ester… Look it up on the web.
Again I say that this is a drop in replacement.
In my humble opinion…!

I would NOT use the blended refrigerants at the auto parts stores. The refrigerant
134a is the only recommended type for vehicles.
I would be best to have some one do this properly. I’d also suggest that you use
change over fittings that have or contain their own shrader valves…Take the old ones completely out after someone has recovered the old R-12. They’re about twice the amount of regular change over fittings.
You don’t have to replace o-rings, drier, or anything else thats working.
The new ester oil will settle on top of the mineral oil and will be moved thru the system with the 134a, so thats not a problem.
So, recover the R-12
remove old shrader valves
install the 134a change over fittings.
vaccuum the system down and add 2 or 3 ounces ester oil in high and low side.
What I do is to let the vaccuum pull the oil in the low side and allow the refidgerate to push the oil into the system on the high side. This keeps you from filling the lines with oil then vaccuuming it out before it enters the system.
I use one of the in-line oil delivery thingie so there isn’t any air/moisture contamination. You won’t need as much 134a as with the R-12… I think the conversion is .80 times the rated capacity in ounces plus allow 2 ounces in the line. So change the pounds to ounces, do the conversion math, then change the ounces back to pounds and fill the motor home, check for leaks, etc.
Good luck,

  1. The desiccant material used in the drier for an R12 system is not compatible with R134a refrigerant.

  2. Minerial oil is not immiscible(doesn’t mix)with R134a refrigerant.

  3. Never follow the advice of somebody who calls a piece of their A/C service equipment a 'thingie".


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If you’re wanting to do this because the curent system is empty and inoperative then you’re going to have to find and repair the leaks first.

Google “Freeze 12”. It works GREAT for “topping off” older R-12 systems. If your system has leaked EMPTY, you might as well find and repair the leak and convert to 134a.

  1. the desiccant material attracts moisture not oil.

  2. I never said mineral oil mixes with R134a… It settles on top of the mineral oil and travels thru the system WITH THE 134a. Do what we did and put the two oils in a jar and shake them up and watch them separate.

3)He doesn’t have to use an in-line flux capacitor oil delivery system, just put the end of the lines from the gages or recovery unit into a jar of ester oil and meter it in the system. Do the low side first. Put the system on vaccuum, shut the valve off on the low side, unscrew the line from the recovery unit and put in a jar of 2 or 3 ounces of oil then open the low side and allow the oil to drain into the system. At this point it can pull air in since there willl be a 30 or 45 minute time limit for vaccuuming. After vaccuuming allow it to sit for at least 5 minutes… the gauges shouldn’t move. After checking the gauges to see that they haven’t moved, shut off the high side valve and then remove the end of the hose from the recovery unit and place it in a jar of oil… open the valve and allow the oil to fill the hose but stop it from letting any air in. Attach the hose back to the recovery unit and charge the high side with 134a pushing the oil into the system. check for leaks… Allow the equalization, crank the motor home, look at the gauges for correct pressures.
Like I said and someone else suggested, you might would like a regular shop do the conversion. If there was a leak before the conversion, you as an independant don’t have a way of recovering it, repairing the leak and recharging. A small shop like ours charges $100.00 for cars and trucks conversions. A little more for larger vehicles. Shop around. Usually there will be a 4 degree temperature loss from R-12 to 134a.
Good luck.

I’ve bought conversion kits at Wal-Mart and performed a VERY simple DIY job on three or four cars. There WAS a performance (cooling) reduction, but other than that… everything has worked fine.

Can’t complain a bit.

Dodge got cold, true story

We had a 1991 Dodge Spirit that came with R12 when we bought it in 91. Through the years the A/C became slowly less efficient and finally the clutch on the A/C stopped engaging (low refrigerant caused this I thought). It was dead for a couple of years.

In 2003 I put a WalMart $30 R134a kit in it on the driveway. I did nothing else, no testing (except with the guage included in kit), no fixing, no O-rings, no drier, no evacuating, nothing else. That A/C blew nice cold air again and still did when I sold it this spring.

A bit of caution:

This was an old car, not very valuable.
Nobody was going to pay anybody a cent to get the A/C working again, therefore there was nothing to lose.

Very much the type of conversions I’ve done and had success with.

I put the WallMArt 134a kit on my '88 Accord a couple of years ago. R12 leaked out through a bad schraeder valve, so I replaced the valve and threw in 134a, and it’s been OK ever since.

just put it in ,wont hurt anything,the oil is a myth,the acid is a myth,the only reason for the whole mess was to sell more tools.I do it every day,and have for years with no ill effect.

good luck.