Nissan Repair: Air Conditioning, ac works, problem child

Question
Basic air conditioning works properly.  Press AC button and as long as the fan is turned on the AC lights and runs.  Turn off the fan AC shuts off. Turn the fan back on AC works.  Depress the AC button and AC turns off light goes off.  This appears to work correct.  Now the problem child.  Turn the selector to defrost - turn fan on and the AC comes on.  Turn the fan off and AC goes off.  turn the fan back on and AC is back on. turn the selector off of defrost ....... AC does not go off.  compressor just keeps cycling like the AC is selected.  the only way to disengage the AC now is to turn the car off at a light and restart the car with the selector anywhere but defrost.  Any ideas?  It acts like AC is latched on when you go to defrost even if you have not turned on the air conditioning.

Answer
Peter,

I do not know if you have automatic airconditioning or not.  Anyway, if the compressor switch does not turn the compressor off when depressed as it should would lead me to thing the compressor relay needs to be replaced.  The relay is located under the hood in the relay box.  Replace it and the compressor should work normally.