2001 f350 heater fan intermittenly runs on low speed only no matter what speed is selected.after a while works fine.anyone else experience this?possible causes to look for?thanks in advance for any help.

 

Never heard this one before... Could be a wire issue or a switch issue...

Are you sure it is running slower, not just blowing on the floor or dash? Vacumn issues can cause something like this.

 

no, blend door operation ok.no vacuum issues so far.fan will not operate faster than slow speed out of the blue then starts running faster.switch in high position whole time.done it couple times now.thinking maybe resistor on fan motor or connection to same acting up?any ideas on this one.thanks

 

Sorry... Got nothing... Might try a new switch...