Converting factory AC to use R134a

[jimbosprint]

I would like to convert the factory AC system in my '72 to R134a so that in the long run it will be easier to service (and because it doesn't work right now). I understand the basics, but I'm learning as I go when it comes to this AC stuff so please explain like I have never heard of these parts. Thanks in advance!

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Questions:

Could I use the stock controls and evaporator, and change the rest of the system under the hood for R134a - compressor, condenser, fittings, hoses, drier?

I found in some research a recommendation to upgrade from the POA valve system to a orifice/accumulator type. I also read something about a switch that cycles the compressor on and off so the evaporator doesn't freeze. Can someone explain this?

Do I need a different expansion valve?

Is there a kit available for doing all this?

Is this a cost-effective way to upgrade the AC system that will also work well?

[junkcarguy]

through lots of searching on this site i had found a thred where a guy in az did the conversion and used a mix of parts and had got it to where he was able to use 134 and it would stau cool at idle when stuck in az stop and go traffic now if i could only find his post again being that i bought all my ac hard parts today keep looking on here its bound to be somwhere

[CUSTOM/10]

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I plan on doing the same and need to know the best way to make it work !

Gary

[Lee H]

About 10-12 years ago I took my factory AC truck to my local AC shop were they evacuated the system, changed the fittings, pull a vacuum, and recharged it with the proper oil and 134. Only cost about $100 bucks. Cooled very well until I tore it down for restoration.

[Davidf]

Interesting timing on this thread. I purchased a 71 this past Saturday with factory a/c. The a/c is non operable, but all there and seemingly original equipment. It is also obvious that 134a was used as the low side valve is of the 134a type (adapter fitting). My plan is to go back to R12.

I live in Austin, TX where summer time temps reach 100+ very regularly. In my past experience with converting R12 systems to R134a it just doesn't cut it in Austin. The reason is mostly the condenser....R134a is less efficient in eliminating latent heat than R12. Thus you need a large condenser to shed that latent heat from the R134a refrigerant. If you live in cooler climates then a conversion usually performs fine (i.e. Chico, California).

Also, I suspect the original factory components are robust enough the handle the higher operating pressure that you get from R134a. The hoses will be thoroughly impregnated with oil and thus probably wont leak out the smaller R134a molecules. The compressors seals may be an issue and I worry about oil contamination. Probably a good idea to have the compressor rebuilt and tell the shop that you plan on converting to R134a. I will disassemble my system and flush all lines, hoses, evaporator, and condenser before switching back to R12.

I know it may seem crazy to switch back to R12, but I have a 30# cylinder of R12 sitting in my garage (about 2/3 full) with no vehicle to use it on. And, I am a certified a/c mechanic (got it online many years ago) so I can buy R12 from the auto parts stores. R12 simply works better than R134a.

Hope this helps...

Edit: Almost forgot...you MUST change out the receiver/drier...oil contamination if you don't. All the other components should work just fine after a thorough flush. And, freezing of the evaporator should be a non issue since the system wont cool as well as with factory R12. So, if it didn't freeze up with R12, it surely wont with R134a.

[engineer_gregh]

I replaced my POA valve with the hi/lo pressure switch, flushed the system, and added the different oil required by 134a. I should have changed my condenser to a high flow as it doesn't cool as good as it should. In hind site I wished I had just had my POA re-calibrated and not gone with the switch. If you call vintage air I'm sure they could give some good advice on the necessary steps.

[engineer_gregh]

David you are correct on the receiver dryer. Any time the lines are open I would replace the receiver dryer, its only about $20 and can prevent hundreds of dollars and frustration by skipping that step.

[Lurayfarmer]

I've done this switch on several vehicles. The key steps are changing the charging fittings, changing the oil, thorough evacuation, and recharge. It is a good idea to change the receiver dryer which is a cheap part. A reputable shop can do this work for a very modest price. Forget anyone who wants to mess with the compressor, valves, hoses, seals, etc. That's just a way for a shop to take money out of your pocket.

As to cooling performance, I've checked vent output temperature with an AC thermometer. It's very close if not identical.

[jimbosprint]

Originally Posted by engineer_gregh

I replaced my POA valve with the hi/lo pressure switch, flushed the system, and added the different oil required by 134a. I should have changed my condenser to a high flow as it doesn't cool as good as it should. In hind site I wished I had just had my POA re-calibrated and not gone with the switch. If you call vintage air I'm sure they could give some good advice on the necessary steps.

Why do you wish you had the POA valve still? Could you replace the condenser and get better cooling?

Another suggestion I found was to add an electric fan to the condenser. What would turn that on/off?

[engineer_gregh]

Jim I like the look of the POA better and I've not been able to keep the compressor from cycling more than I like at highway speeds. I've done the fan on the condenser and wired it to the power lead to the compressor so it only runs with the a/c on, and it does help a little. Its off right now but I'm either going to put the fan back on or change the condenser. Bill I'm glad you've had good success with converting your's over. Other folks I know and trust have said the same thing. More often than not I've been advised that the increased pressure does typically require changing the condenser.

[Katrina/10]

An 87 evaporator will fit in the original box.

[Davidf]

Originally Posted by Lurayfarmer

I've done this switch on several vehicles. The key steps are changing the charging fittings, changing the oil, thorough evacuation, and recharge. It is a good idea to change the receiver dryer which is a cheap part. A reputable shop can do this work for a very modest price. Forget anyone who wants to mess with the compressor, valves, hoses, seals, etc. That's just a way for a shop to take money out of your pocket.

As to cooling performance, I've checked vent output temperature with an AC thermometer. It's very close if not identical.

Temps between R12 and R134a will be close until you get to about 95 degrees outside air temp...above 95 degrees, you will probably start to see increasing difference between the two refrigerants. This is due to the condenser not being large enough to shed the latent heat from the R134a. Now, with that said, my experience is mostly based on BMW a/c systems. It could be that GM oversized the condensers to begin with and thus this is less of an issue on our trucks. But, I doubt it.

As for the receiver/drier, most think if you open the system you MUST change the receiver/drier. I don't adhere to that camp. If you open the system, you can reuse the receiver/drier because when you evacuate the system, you boil the moisture out of the receiver/drier. That is why you leave the vacuum pump running for at least 30 minutes. Longer in cooler weather. But, if you change oil/refrigerant types, I say you MUST change the receiver/drier. But, changing the receiver/drier is never a bad idea, especially if they are old.

[brown7373]

Does anyone make a parallel flow condenser for our trucks? I haven't checked in a couple years.

I got one for my 72 Cutlass and it made a MAJOR improvement in cooling. Also, had the POA recalibrated for 134A and I get 30-35 degree air from the vents with little loss at traffic lights.

Basically you flush out the system, replace all the O-rings with ones for 134A, add a new filter dryer, evacuate the system and recharge with 134A at 75-85% of the R12 amount. Don't pay attention to bubbles in the sight glass, because it doesn't work the same with 134A. I used my existing hoses, that were impregnated with the old R12 oil and have had no leaks. I also bought a Haynes A/C Manual, that helped me understand the whole A/C theory.

[Davidf]

For the same reason you replace all the O-rings to R134a compatible material is the same reason I worry about the front shaft seal on the compressor. It would be wise to replace the compressor seal as well. And, the mineral oil must be thoroughly removed from the compressor and replaced with PAG/Ester oil. Mineral oil (R12) and PAG/Ester oil (R134a) do not mix. Mineral oil and R134a do not mix. So, any left over mineral oil will find the low point in the system and say there. That is usually the condenser and thus condenser efficiency can be slightly compromised.

[CUSTOM/10]

Lots of good info here !!!

OK, I'm an HVAC Tech but just don't have much experience with automotive A/C. I did some research on other forums and there's more than one way to do the conversion. The following is the approach I'm going to take partly because I'm doing a ground up resto-mod and I have a new sanden compressor.

* New Sanden Compressor
* New condenser coil ( Parallel flow for R134A )
* New drier
* New custom lines set
* Adjust the original POA valve to 26.5 PSI
* I already have electric fans with a controler that brings on the fans for the A/C.
* Replace all o-rings
* Flush the system
* Add the proper amount of PAG oil
* Re-use the remainder of the original system.
* Evacuate and charge the system to 75-85% of the original charge

At least this is what I'm thinking at this point.

Gary

[Davidf]

You plan is sound. The new condenser matched to R134a refrigerant will make all the difference. I installed a Old Air Products system in my '52 truck (all matched to R134a) that utilized a Sanden compressor, electric condenser fan and it will freeze you out. Good luck.

[mrein3]

I added AC to my non-AC truck.
I never was a certified AC mechanic but I did LOTS of AC service in a small, non-chain shop while paying my own way through college. Everything I learned about automotive AC was on the job training.
Since I have WAY more time than money, I chose to put in all stock AC parts, and adjust the stock POA to work with R134a.

I'm approaching my 5th summer running R134a with everything else stock with ZERO problems. Other than the stupid o-ring on the schrader valve on the POA leaks.

I did a write-up on it here:
http://67-72chevytrucks.com/vboard/s...d.php?t=478564

I hope this helps.

[leddzepp]

134 will leak out of the front seal on a rebuilt stock (A6) compressor eventually. I went through four of them. If you live where it gets HOT (and I don't mean 80) r134 will not work well in a factory system with the stock condensor. I will only use R12 on a factory system.

[CUSTOM/10]

How much oil should be put into the system once it has been flushed of the old oil ?

Gary

[jimbosprint]

I got an email from John at Old Air Products. He said this would convert the truck to a fully functioning R134a setup, and it all bolts in. What do you AC experts think about doing it this way?

Originally Posted by Old Air Products

Parts list:
Condenser- 11-7201 $205.00
Drier- 21-4215A $65.00
Compressor- 21-2201SH $345.00
POA Update- 50-2551A $95.00
Hose Set- 95-7215A $110.00
Liquid Line- 95-7216 $24.00
Tube Set- 50-7220 $48.00

This is everything under the hood. If you have any questions you can email or call me.

[Andy4639]

I've been running 134a in mine for as long as I can remember and no problems. I bought the kit when I did it from Classic air. I had the old parts that I took off another truck first but the old A-6 compressors wouldn't hold up. I since have swapped a 6.0 in it and it runs great now to. I swapped condensor acumalator did away with the drier, and put the orfice tube in the bottom line. I bought the hose kit and brackets along with sanderson compressor and ran it for several years before I did the LS swap.

http://www.classicautoair.com/GM_OEM_Parts_Engine.html

[Bigdav160]

Parts list:
Condenser- 11-7201 $205.00
Drier- 21-4215A $65.00
Compressor- 21-2201SH $345.00
POA Update- 50-2551A $95.00
Hose Set- 95-7215A $110.00
Liquid Line- 95-7216 $24.00
Tube Set- 50-7220 $48.00

I would change a couple things.

I'd buy a Sanden A-6 replacement
Forget the POA update as it converts your system to a cycling system designed for orifice tube use. You'd have to add a evaporator core to the above quote or fabricate an inline tube/filter.

Other than the pricing being a little high, it should work.

Oh, if using a parallel condenser I would not undercharge the system.

[kwmech]

Anybody have a part number for a sized condenser that is built for 134a that will fit in the same mounting holes as the factory tube/fin condenser?

[Vintage Windmills]

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[hdff]

sub'ed this is my next project