Heater Control Problem

[Unregistered]

I have a 90 535i that has a heater control problem. The temp control knob for the passenger's side does not stop heat flow even when the knob is in the off position. I just disassembled and cleaned the heater control valve. I also tested it by applying current to both sides and valves moved...so it looks like it's okay. Any ideas where the problem lies?

Thanks,
Danny