Not knowing when the fan motor starts and stops, I would check this-if the blower doesn't run then you hit a bump, pothole, etc. and it runs, its probably the bushings in the motor. The only fix for this is replacing the blower assembly. If the motor isn't manufactured/remanufactured correctly, then the bushings which actually turn the shaft by inducing the electrical field are shot. A simple test is the next time the blower stops, hit the motor with your hand to see if it will start.
There's a short in your main line going to your fuel heater.
Heater blower motor is defective and locked up, or possible short in the wiring.
You probably have a shorted wire going to the motor or switch. You'll have trace the wires and find the damaged section.
There is an electrical short to ground in the fan switch or in the blower motor itself.
not usually!!if fuse is blowing out check for short!!
could be head gasket problem. does your heater work? might need heater core , clogged up. do compression test. or bypass heater core and see if that works.
bottom element is probably bad. another sign of this is that you run out of hot water fast.
Beause there is probably a short/bad connection in the switch, or the blower motor itself
Could be, Low on coolant, A stuck open thermostat, A plugged heater core, A faulty temp blend door actuator,
The air doors maybe stuck. Or selector switch is not is not operating correctly.
If your problem is that the cold air stops blowing out the AC vents and transfer to the defrost or the heater vents, I have had this on my 99 Astro. There is a small vacuum line that runs from the Drive Side Valve Cover near the front across the front of the engine over the Air Conditioning components. If this line gets cracked or broken, when you are going up hill and the engine requires more vacuum for fuel there isn't enough vacuum to keep the Air blowing out the AC vents. Check the line for cracks or broken areas.
Perpetual motion machines do not exist. There is no machine that will keep on moving by itself without any added power. Windmills are driven by the wind. When the wind stops blowing, the windmill stops turning.