A/C Cycling Switch

OK I give up! Can't understand what I'm doing wrong. Should be a simple thing. I would think.
Put a new Factory Air switch part # 35720 in there a few weeks ago. Worked for a little while and then starting freezing again in cooler weather at night on the highway. OK tried to adjust it again and lost one of the screws. Went to buy another switch and could only get an AC Delco. The delco had one adjusting screw and regardless of which direction or how far I turned it, the compressor would never shut off.
Ordered a new factory air switch and put it on today. AC running, pulled the power off the fan to make evap freeze. This switch has 2 screws. One says "cut in" and the other "cut out". Evap ices up. Low Side drops down to 10 psi and compressor won't cut out. Tried adjusting screws nothing happens. Pull the plug off the switch and the compressor stops.
So, picking up heat in the engine compartment? Don't think so. I have planty of cork tape over the bulb and about 4 inches of the wire. Covered that in heavy rubber electrical tape. Tried adjusting again. I can get it to cycle on/off but it doesn't hold the settings. If I get to go off at 30 psi the next time I try it just keeps running. If I get it to kick in at at 50 psi the next time I try it it runs up to 75 psi and still doesn't come on. Kept playing with the screws until boingggg!!!! One goes flying. OK took the other one from the old switch and started over. But can't get a consistent setting.
So what am I doing wrong?
Can someone recommend a better switch that this $15 POS? The delco seemed better built but I couldn't get to work right either. Is the problem that they're set for R-134a and not R-12 anymore? Either way I would think it's sensing temp. So freezing is still freezing.