Probably burnt trace in the IRCM circuit board, OR failing relay. You can remove it and drill the rivets out that hold the black cover to the circuit board, then inspect all of the relays and board. You can also solder on new relays if you wish. It's not that hard to do. I just had my '93's A/C cutout relay give me some fits, exactly as you describe (whack it and the a/c comes on, hit a bump a/c goes off), pulled it apart found bad relay. Grabbed a relay I had already, soldered it onto the board and it's good to go. New IRCM is about $150 IF you can find one. They are on national backorder. You can get one from a junkyard too, I used one from a Taurus to get by for a few days.