The low pressure switch should be threaded into the accumulator tank or line going into the accumulator of the suction side coming out of the evporator. It is a two wire connection and the switch threads directly into the fitting and has an o-ring for sealing. It is a schrader valve type of switch, like a tire valve, which means you can remove the switch without losing the freon. The switch is designed to open when suction pressure drops below a preset point, usually about 30- 35 for an R-12 system. If the R-134 charge is a little low the suction pressure will drop below the preset and shut of the compressor, which is what I think is happening to you. Also with R-134 freon many times the low pressure switch is set lower, like around 20 psi. Some low pressure switches are adjustable so remove the connector and look down into the switch connector and see if there isn't a small adjustment screw. If not you can replace it with one from NAPA. If it does have an adjustment, turn the screw CCW for lowering the pressure. Make small turns like an 1/8 of a turn to adjust. You have to have guages attached and engine rpm needs to be at about 1200 rpm to set the adjustment properly and also to check high and low side pressures. What are your high and low side pressures at 1200 rpm and at what is the ambient air temp at the front of the condensor? If youcan get me these I can probably help you through this. I said 2000 rpm in my earlier post when I meant 1200.

John