Here is the deal. My 80 Monte was originally a R12 system with only the low side pressure switch. No high side switch. I converted the system to 134A a couple years ago. New compressor, dryer, and orfice tube. Last year I charged the system and lost track of how much 134A I actually had in the system. I messed with it several times. Let some out, put some in. You get the idea. It would work good at idle or around town, but going down the highway it would blow hot. This year it did not work. So I brought my A/C stuff home. I found apparantly I have a leak. Witch is ok because I needed to start over. I vacuumed down the system and it held vacuum for twenty minutes, so the leak is very small. I charged the system. I found where the system wants to run for pressures. The problem is with the low pressure switch plugged in it wants to cycle the compressor clutch too much. So I put a jumper wire in the low pressure switch plug. It works good now. Held the throttle up and it gets colder and pressures look good. So on to my question: Is there a different low pressure switch for 134A that I should be using? What is everyone else using for the conversion from R12 to134A? Is the systems with a high pressure switch different? Thanks in advance for any replies.