Corolla 93 - AC Button lits on with 2K rp whilst fan is off.

Corolla 1993, 180,000 Kms, 1.6 GLI 4A-FE engine.

Normally my AC button functions only when the fan is switched on, i.E. If the fan is off then the light on the AC button is off - even if it is in the pressed position.

Recently I faced a problem when my engine wouldn't start - so my mechanic changed my delco and swapped my engine controller. But the problem got fixed when I put my original controller back. Now however, my AC has developed this problem - as soon as I press the AC Button (even with the fan off) - the rpm goes to 1.8K - 2K and I can hear the AC Fan belt running. And there is no cool air when switching the fan on. My mechanic has pulled & plugged the "AC MG" relay as well, but the behavior is the same. I seek your advice on what the problem could be. Or where does the AC button connect that triggers the rpm and fan belt on.