87 Sierra Conversion to R-134

[nuckollsr]

I inherited an 87' R1500 a few years ago with very low miles on it and good body condition. Dad had it converted to R-134 some time before he passed his truck to his son. The a/c worked 'pretty good' but was prone to evaporator freeze-over. I've put up with it for about 7 years but the compressor went south and I set out to replace it.

Reading up on GM R-134 systems, I noticed that many vehicles replaced the simply low-pressure cut-out switch with a pressure cycle switch. It served the same purpose as low-pressure cut-out but added hysteresis to open at about 20 psig and re-close at at 35 psig. This had the effect of cycling the compressor to limit the evaporator's lowest excursion. The switch is field adjustable so that the technician can tweak the setting for max-cool without freezing.

The new, smarter switch looks just like the older low-pressure cutout. However, the newer switch has a larger thread on the order of 12mm and wont thread onto the 1/4" port on stock R-12 receiver dryer.

Is anyone aware of an adapter for this application? Or, perhaps, there is an alternative receiver drier with the larger port to fit the R-134 switch. I'm not adverse to getting on the lathe and making my own adapter but I'd rather purchase the parts for an elegant trade-out.