control knob for simpson delta 422 model 36e422p+ o3?

Without being there to look and check things it is impossible to say why the machine won't run. Especially as you say you have disassembled part of the machine & disconnected power etc. If you don't know how to put it back together then call someone out to do it. Fairly old model Simpson and to be honest it is not really worth mucking around with.

Lincoln Appliance NZ
January 2012