OK, so I have been farting around with the A/C system on the truck. I am using a cheap alternative hydrocarbon for my refrigerant right now. I am "testing" the system with this alternative. I removed the R134a I was using and not getting good results with. I changed the drier for a new one and vacuumed the system for an hour. I recharged it with the alternative until the compressor stopped cycling when the engine rpm was brought up. I quickly noticed the evap tube below the orifice tube was frosted and iced over with a thick layer. To the point where I could not pick the ice off with my fingernails. The low side PSI was at about 34 at idle. I reduced the PSI to 30, same thing, reduced to 28, same thing, reduced to 24, same thing. Anything under about 32-33PSI at idle will make the compressor cycle at higher RPMs. The vent temps do not show much over ambient outside temps.

I have a theory: I am using a red orifice tube with a smaller orifice than the blue tube. The red tube is supposed to be better for R134a and the blue tube is for the stock R12. The replacement refrigerant is closer to R12 than R134a so I am thinking that I am either freezing the evap up into a block of ice or I am freezing up the tube to the evap and by the time the refrigerant gets into the evap, it has already turned to gas.

The liquid line going into the condenser is very hot while the line coming out and going to the orifice tube is warm to the touch. I feel the condenser is doing its job very well.

The drier is warm and sorta backs up the last part of my above theory. I am thinking about investing in a variable orifice tube or at least trying the blue one this time.

Advice is appreciated. I'm experimenting and willing to share any results if anyone has a suggestion.