The fan stays on at low speed when the resistor is disconnected? Someone must have wired 12V through a resistor between the resistor and fan. As Alice said, curiouser and curiouser.

Try this. Disconnect the resistor from the fan, jump the AC pressure switch and measure voltage upstream and downstream of the resistor. Should be close to battery voltage upstream and somewhat less downstream. That will tell you that the low speed circuit is working.

I don't know how the output of the high speed relay meets up with the output of the low speed relay so I don't know where to recommend a test of the high speed circuit.

Remove the fuse that should power the fan and see if the fan continues without that fuse. If the fan continues, remove the other fuses one by one until you find the fuse that keeps it powered. You might want to skip the radio fuse if you still have the factory radio. I have no idea what to expect if you pull the engine ECU fuse with the engine running. The K-Jet should go to limp mode but you might get a check engine light.

Sixto
95 S420
87 300SDL