GM-GMC: HVAC blower motor quits blowing on high., volt drop, fan switch

Question
Hello, I have a '94 Winnebago Motorhome on a P30 Chevy chassis that the blower motor will blow on high cool for a couple of minutes and then shuts off.I can switch the fan motor down to another speed and it works ok. The controls are electronic with vacuum actuated doors. Do you suspect the problem to be in the controls( fan switch), blower resistor or motor? I suspect the fan switch.
Thank you....JD

Answer
no i wouldnt condem the fan switch.i would test with a volt meter to see if you are geting voltage to the motor when it creates the problem if you have 0v then you could condem the switch if it has correct supply voltage then i would do a volt drop test accross the motor if there is any voltage then the motor is bad. because the motor may have an internal short which is causing it to over heat and lock up due to excessive current draw which isnt experianced at lower speeds because the lower speeds will not draw as much current threw the motor