You can order the pressostat online and have it overnighted to you.

The pressostat gets 12v to it when the A/C is called for by the switch on dash. If the pressure in the system us above ~25psi, the pressostat will close and energize the clutch on the compressor (on some vehicles the power goes through a high temp override sensor on the back of the compressor).

When the ~25psi is reached in the system, the pressostat will open and the compressor clutch will be de-engized until a pressure of ~40 psi is reached in the system when the pressostat will again attempt to energise the compressor clutch. Hence the cycling.

Hope this helps.

DEWFPO
--
1998 S90 068,300 and 1995 964 152,300