Re: 1956 Packard air conditioning system

Posted by HH56 On 2023/7/18 21:17:49

Some people with older AC systems from all mfgs have reported changing to R134a without any major changes while others report nothing but problems -- even after sending their various valves to places that are supposed to rework them to work with R134a. Refrigerant leaks with old components are also an issue.

As far as the modulating valve the calibration is what needs to be changed. There is roughly a 2 psi difference between R12 and R134a at the same 38F or so degrees the modulating valve needs to hold at the evaporator. While the screw on the end of the valve can do the adjustment it takes some time between adjustments to stabilize so there may be a bit of back and forth adjustment and will require good pressure gauges to get it just right. The valve needs to keep the evaporator warm enough not to freeze over but still cold enough to be at the optimal cooling temp -- between 32 and 40F is where Packard wanted it but toward the higher end gives more of a safety margin so the evaporator doesn't freeze. The expansion valve may also need a similar recalibration as it is also pressure operated and could flood or starve the evaporator if not set fairly close.

The bigger issue with R134a conversions is the old stock hoses and fittings. The R134a molecule is much smaller than the R12 molecule and the old rubber hoses frequently let the refrigerant leak as does the flare fittings and the seal on the compressor. Hoses most likely will need to change to new barrier types and flare fittings may need to be opened to have a special sealant applied to the mating surfaces and then retightened. Oil in the compressor also needs to change to one compatible with R134a. If the compressor seal leaks there is not a lot that can be done other than change the compressor to a modern type compressor with internal components compatible with R134a.