1994 accord VTEC 260k miles on body, 170k on motor and tranny. When i turn the AC on (the actual AC button) the car starts to shake rather violently. When i disengage the button it stops. When the fan is on, it doesnt shake or anything. Just wondering what would cause this and how could i fix it? AC does blow cold.

 

I would clean out the idle air control valve using some throttle body cleaner. It is bolted on the upper part of the intake manifold near the throttle body and the firewall. It is held in by two 12 mm (maybe 10mm) bolts. It has to coolant hoses going to it. It also has an electrical connector to it.

You may want to drain the coolant. Remove the valve and clean the screen and valve. You may want to clean out the passages for the coolant. Check that the hoses are plugged up as well.

I think there is a thread in the DIY forum about this.