AC compressor always running? 1986 190D

[xweezyx]

I have a non-diesel related question about my 190D I just acquired. The AC blows cold, and its nice. The weird thing is that the compressor clutch never disengages. The only thing I could do to turn it off was pull the harness off the compressor. unplugging the pressure switch had no affect. Anyone come across this? or have some good diagnostic info I can look at? Im pretty good at figuring out these little electrical things, but haven't been able to find the info I need. Thank You!