What are your pressures? Have you unplugged your pressure switches? If you unplug the high pressure switch and it kicks off, the switch is probably stuck closed. You need to get a wiring diagram and trace it electrically.

Also, you should make sure that air is being drawn over temp sensor. You can do this by holding a cigarette(yuk) or other safe source of smoke near the air sample grille near the rear view mirror. It should draw smoke any time the ignition is on. If not, find and check the little fan that is probably to the right of and behind the glove box. The location varies in the 124 series.

It's always best to take this approach instead of just guessing and replacing parts.

Good luck,