AC clutch always stay on

I have a 92 Mazda MPV. When I turned on AC the compressor clutch always
stayed on and would not cut off. I measured the vent temperature was at 32 F
.. I checked thermoswitch manually it would cut off below 32 F . If I
disconnect the thermoswitch the AC compressor would cut off. I measured
Freon Low side pressure at 30~45 PSI. High Side at 130~150 PSI.

I am wondering what controls the AC clutch? Pressure switch?
Any idea?