Insure the temperature switch is in tight. It is not a pressure boundary, just a tapped hole that it screws into w/ a straight thread. You need it tight to read correctly. Might help to coat the end w/ heat sink compound. A resistor wouldn't work. It is not an analog sensor, just an on/off switch that controls the AC compressor clutch directly. You would have to find a lower temperature one that fits.

Have you measured your refrigerant pressures? If too low or too high refrigerant fill, it won't blow very cold air.