Nissan Repair: AC compressor always on, nissan frontier, frontier 2

Question
I have a 2001 Nissan Frontier 2.4L manual transmission.  The AC compressor is always on (even with the dash button and fan switch off) when the engine is runnning.  I removed the AC relay (it appears to be good) and found that there is always power to the relay coil (with engine running).  The Chilton wiring diagram I have shows a 'thermo contol amplifier' that I would like to check. Where is it?  The fan works correctly, and the light behind the AC pushbutton comes on when it should.  What else can I check?

TIA,

Too cold in Texas

Answer
David,

If the clutch stays on with the relay removed it is the relay.  But, from what you say there is power to the relay all the time.  If this is the case the control panel in the truck should be checked to see if it is defective.  I would think that is where the problem is.  The amplifier is under the dash on the passenger side by and on the air box.