im having problems on my 80sd getting temp wheel to go from heat to cool,at cool it gives heat only,sometimes at start up it will remain at cool and even give ac if compressor set on on.ive replaced foam hose,have heard servo park itself at shut down.no vac problems.whats nest calibrate temop wheel-how is this done,amplifier?

__________________
95 e320,87 sdl,79 300sd