By-passing heater control for Blower

This friend of mine just by-passed his heater control head on his '92 Roadmaster because he lost blower speeds(all). I'm not sure if it is a problem with the power control module(likely) or heater control head. I've worked on a couple of these before and believe that possible damage can occur to the control head by by-passing the control head?

He has a switch controlling the blower so we know the blower is o.k.
Can any damage occur by doing this by-passing is my question? It seems the ecm controls the heater control head etc.

Thanks