Hi All,

I wanted to share my experience converting my factory air system to 134a refrigerant, hoping it will save you time and money.  After I changed the parts, I got my system charged professionally and it works amazingly well, blowing ice cold at the vents.  Here's what I did:

I started with a call to Old Air Products (oldairproducts.com) from Texas.  I'm usually the guy who researches everything alone and then buys the parts online without ever interfacing with a human, but A/C is one of the only parts of a car that is (was) a mystery for me so I decided to call on the experts.   I couldn't find complete information on their website, so the call was essential.  They were technically competent and no pressure to sell.  I told them I had a non-working factory air and wanted to convert from R12 (I assume that's what was in there) to R134a.  The compressor appeared to be original and its internal condition unknown, so a remanufactured one was recommended to avoid problems.  I chose an A6 over a modern replacement version (Pro6TEN) since I preferred the stock appearance.  Here's the parts list and Old Air Products Part Numbers:

  • Remanufactured A6 compressor - 21-3215-10 *
  • New high pressure hose - 95-6507
  • New suction hose - 95-6508
  • New receiver/dryer -21-4215A *
  • STV Upgrade kit - 50-2500P
  • New expansion valve - 25-0054
  • 90 degree 134a adapter (low side) - 91-954M
  • 90 degree 134a adapter (high side) - 91-953M

*Note that the compressor had a smaller pulley than original and the receiver dryer was smaller than original.  See the "important notes" section below for details and talk to your supplier about options.

I encourage you to call Old Air Products (or your preferred supplier) and talk to them about what you want to accomplish.

Once the new parts arrived, I started by removing the old hoses, expansion valve, hard line, receiver/dryer, and compressor.  I flushed out the condenser with AC Pro Power Clean and Flush that I bought at the auto parts store.  Also flushed out the hard line from the expansion valve to the dryer (after removing it from the car).  I did not flush the evaporator.

After everything was clean and blown out with compressed air, I started assembly.  The STV upgrade kit comes with everything you need to change the system to cycling clutch type, so I followed the instructions and everything went well. I made sure the compressor had the recommended amount of PAG 150 oil (10 oz), and assembled all the hoses and parts.  The kit contained enough new O-rings to do the conversion 3 times, haha, so don't worry if you drop one into the frame rail.

After everything was back together, I went to Autozone and borrowed a vacuum pump and a set of A/C gauges.  Following the instructions, I pulled a vacuum and let it sit overnight.  No leaks!  Ready for charging!

I wasn't about to charge it myself so I found a reputable local shop and let them do their thing.  I mentioned to them that the service manual called for 4lbs (64oz) of R12 for a completely discharged system (as mine was).  I also gave him a conversion factor for R134a I found on the internet which said I'd need 53oz of 134a, because apparently less 134a is needed than R12.  It turns out that the system stopped accepting refrigerant after 34 oz was delivered, and the system now functions perfectly.  I can't explain the shop manuals 4lb requirement nor can I explain the conversion factor an internet "expert" suggested.  34 oz of R134a works so I'm sticking with that!

I took a few measurements to see how the A/C would perform on a hot day.  With an outside temp of 88 degrees at around 2:30 with full afternoon sun, I measured 35 degrees at the driver side vent in idle and 32 at the center vent.  At cruise speed and at higher rpm, vent temps are much lower - I measured 28 at the drivers vent and 24 degrees at the center!  Outside surface temps of the car were over 100 but inside was comfortable.

I've driven the car on a couple of 90 degree days and have been pleasantly surprised that old school A/C in a convertible can perform so well.

A couple of important notes:

  • The A6 compressor I bought came with a 5" pulley (measured overall diameter).  The original compressor had a 6" pulley.  I could have sent the compressor back for an exchange, but the tools for changing the pulleys can be borrowed from Autozone so I did the swap myself.  Fortunately, my original pulley was in great condition.  Make sure you specify when ordering.
  • If you're going for concours quality (I'm not), the paint on the reman compressor is not correct.
  • The R134a fittings do not look like the originals, but you might get black caps or paint them to make them less visible.
  • The hoses from Old Air Products look like the originals except for writing on them (manufacturer and part number and such).  You might be able to remove the writing with a solvent.  It's not obnoxious, but not concours correct. They're manufactured with modern materials and compatible with R134a refrigerant.
  • The receiver/dryer came unpainted raw aluminum and is smaller than original, factory brackets will need modification.  Stock ones are hard to get because the cores are rare.  You could send your original to be rebuilt if originality is a concern.
  • The expansion valve looks original but seems to have more coil length than original. The coil is copper so again, some black paint would help hide it.
  • The STV conversion basically removes the internals of the valve and closes off the vacuum actuator functionality.  The valve will appear stock after modification.  There is a small relay that needs installed, you'll have to hide it if you want a factory appearance. 

I hope this post helps you.  Sorry I didn't take progress photos - I hadn't thought of blogging the experience until I was done.  I added a few "after" photos below that give you an idea of what the parts look like. 

Total cost was $675 for all the parts, and $175 for the refrigerant and labor to charge the system.

If you have any questions or need related info, just ask.

-Mike

Photo 1: Receiver/Dryer in raw aluminum.  Note that the replacement is a shorter "bottle" than original.

Photo 2: This is the remanufactured A6 compressor and the R134a fittings.

Photo 3: Another view of the fittings.  I ordered 90 degree adapters because of the size of the gauge and charging system connectors.  I didn't think straight fittings would allow those connectors to fit.

Also note the writing on the low pressure hose.

Photo 4: The modified STV (left) looks original from the outside, as does the expansion valve.  The silver relay on the right is the compressor cycling relay.  When the surface temp of the evaporator outlet gets too cold, it shuts off the compressor.  Seems to activate somewhere between 15 and 20 degrees.

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Comment by Michael Forte on July 25, 2018 at 11:17pm

Dana, here are the instructions from the Old Air Products STV Update Kit.  I installed exactly as pictured.

Comment by Dana G Cooper on July 25, 2018 at 1:00pm

Mike, if you are on here right now, how did you attach the expansion valve capillary and cycle switch capallary to the evap outlet and at what position. thanks

Comment by Anders on August 21, 2017 at 1:22am
Thanks.
If possible maybe you could update those parts on the original post. It will help others in the future as this thread is the go to place when fixing the A/C.
Comment by Michael Forte on August 21, 2017 at 12:53am
Sorry It took so long to reply. I used part numbers 91-953M and 91-955M. $12.50 each.
Comment by Anders on August 16, 2017 at 4:50am

Thanks for updating with the parts numbers. Looking through the list and maybe you could clarify the two 90 degree 134a adapter (high and low side). Been searching the old air site and found these:

Adaptor, 90 Deg, 134A, 1/4", Low Side

Adaptor, 90 Deg, 134A, 3/16", High Side

Are these the ones you meant above?

Comment by Clovis on July 29, 2017 at 7:30pm
I got mine from old air products. The issue I've had with mine seems to be a common one based on their feedback and that of other online forums. Not a deal breaker just looking for the fastest cool down of the car. I'm not one to be satisfied until I've tried it twelve ways from Sunday.
Comment by Robert Gonzalez on July 29, 2017 at 7:05pm
Yeah, opgi is super over priced , but their service is that they have everything under one roof for people who don’t want to look all over for what they want. As for rock auto, I actually hate the idea of being able to fidget with the adjustable one. I have the opgi kit, it worked perfectly the first time, I didn’t have to mess with placement because the instructions are clear as to exactly where it goes. *crosses fingers*
Comment by Clovis on July 29, 2017 at 11:21am
That appears to be an adjustable one Tony. I have not tried that part, the one I have is non adjustable and more expensive.
Comment by Tony and Ginny 429 on July 29, 2017 at 10:58am
Clovis
The part number you listed
Is that for the adjustable STV kit at Rock Auto or the non adjustable one

I am asking because i know you had to fuss with its location to get it to work correctly per a prior post


Enjoy
Comment by Clovis on July 29, 2017 at 10:28am
Old air products is also just a reseller of the update kit. It's a non adjustable one and if the the temperature sensor isn't positioned right it will cycle the compressor to often or not enough. With an adjustable cycling update you can adjust the temperature and not keep having to remove the tape and readjust it.

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