In further work on this dryer I found the centrifigal switch had a problem in that two contacts inside had been arcing and occasionally sticking together. This switch was taken off the motor and the cover taken off it. The contacts in question were cleaned up using a nail file and reassembled on to the motor. This fixed the problem although I would like to get a new switch assembly it does not appear to be available to buy . If anyone can tell me where to buy this switch I would appreciate it.