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  Losing My Cool...

  May 27, 2024

  OK, right when I didn’t think anything else could go wrong this spring, the front oil seal on the GTOs air conditioning  compressor decided to give up.  The result being oil and fan belt debris flung all over the inner fender and underside of the hood which, in turn, ruined the under-hood insulation installed by the previous owner.  I recalled recently thinking “Gee, there’s not a system on this car that I haven’t touched.”  Then BAM!  Something else to fix.  Joy.

  The previous owner told me that at one time he had to replace the muffler on the AC system.  That’s the silver-colored can thing attached to the side of the compressor.  Not all GM divisions of that period use them on their cars, Chevrolet being one of them.  Anyway, when the muffler was replaced (sometime around 2006, I think), he was still able to find someone with the R12 refrigerant to restore the AC system back to factory standards.  Today R12 is no longer used.  The current automotive refrigerant is R134a. 

  Converting to the new refrigerant is also not as simple as “out with the old, in with the new.”  The lubricating oil is different too.  So, the conversion process requires a complete flush to remove all the old oil before the new oil can be introduced.  Additionally, all the O-ring seals are different and must be replaced.  Cracking the system open to change the O-rings will require the replacement of the receiver/drier as well.  And, I’ll change out the expansion valve too because, in addition to the drier, replaceing that is also required to maintain the warranty on the compressor.  Because R134a refrigerant operates most efficiently at pressures different from R12, so the POA (Pilot Operated Absolute) valve must be adjusted to work effectively.  The final solution could be in one of two forms, both of which would be expensive.

  I could replace the compressor with a modern design and a POA eliminator switch.  Although either way will work, I chose to replace the compressor with a remanufactured unit and re-adjust the POA valve to work with the new R134a refrigerant, along with the new expansion valve and receiver/drier.  Doing that will allow me to retain the stock look and smooth operation of the original I’ve been trying very hard to maintain.  To do the job completely, one would normally replace the condenser out in front the radiator with a more efficient unit designed for R134a.  The old condenser will stay as the system will still function adequately with it.  Doing the other work is already expensive enough. 

  Disassembly went well.  I was pleasantly surprised to find that the muffler and hoses the previous owner replaced are newer style barrier hoses rated for use with R134a.  I had been led to believe that the regular old hoses for R12 would not hold refrigerant long-term if the R134a were used.  This saved me a couple hundred dollars. 

  I found that many of the O-rings related to the parts the previous owner replaced were also the green colored nitrile versions also rated for R134a.  That was a good thing because despite all the O-rings included in the service package from Ames Engineering, there were a couple of odd sizes found on my system that weren’t included in the kit.  Luckily, those were the newest and in great shape, and were able to be reused.  I also marked each joint with a red marker after I tightened it.  This would help ensure that I didn’t miss any connections.  

  Adjusting the POA valve was an eye opener - literally.  All the YouTube examples of this procedure seemed to be done on Chevrolets, which only emitted a slight “pop” followed by a hiss during the adjustment process.  I now know why the AC system on this Pontiac required a muffler.  As I was introducing pressurized air into the expansion valve to make my POA valve cycle, it would give out a blood curdling toot like a demented flugel horn every time it triggered.  It scared me silly.  Anyway, the adjustment amounted to a 2psi to 2.5psi reduction on the low-pressure side to work best with R134a, and indeed took only about 30 seconds.

  Once done, it then went back to the shop to undergo a vacuum test before filling the system with a fresh charge of R134a.  

   

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