My vehicle is a 1992 535ia (e34)

I have a problem with my AC system that I am trying to sort out.
When I turn on the AC. The compressor will come on. AC is ice cold.
When I turn off the AC , the AC compressor will
continue to run. It will run basically until I shut the car off.

I have completed the following work on the AC System:

Conversion to R134A. With New receiver drier.
The system is fully charged and has correct amounts of
R134A and PAG oil.

Installed new auxillary fan resistor after fuse #25 blew.
Auxillary fan is working.

I swapped the HVAC control panel with one that I know was working
in another vehicle. So I have eliminated that.

Has anyone had a similar problem? Or can offer some advice?
Could it be the AC Control module or some relay that is bad?

Thanks in advance for any Ideas.