Blower turns itself on and off & thermostat is off

[hardwood62]

Coleman DGATO56BDE - furnace blower motor comes on and runs for several minutes and then turns itself off and will repeat this at random intervals and will only stay off if furnace is switched off at the control box or breaker is turned off. Thermostat is not calling for heat ... is turned off, and fan switch is set to off. If fan switch on thermostat is turned on fan runs until switched off - then will do the random on off again ... sometimes it takes several hours until it turns itself on. Any idea what part I need?

[DaleM]

Sometimes enough heat is generated by the sun beating on the roof stack to cause enough heat build up in the heat exchanger to cause the fan switch to turn the blower on. The fan switches used in furnaces these days are set to come on at fairly low temps, 115-125 degrees. Your switch may be getting weak and you could replace it but that may not keep the fan from coming on. DO NOT put a fan switch with a higher temp value in your furnace.