THE HEATER FAN ON THIS VEHICLE DOES NOT OPERATE BY TURNING THE SWITCH ON. WITH THE SWITCH ‘‘ON’’ THE FAN WILL START WHEN THE TRUCK HITS A BUMP. IT DOES NOT OPERATE AGIN AFTER THE TRUCK IS TURNED OFF. ANY IDEAS ??? THANKS …
Probably a bad blower motor.
Electrical connections develop corrosion over time, even within plugs that have been connected together all this time.
Could be the blower motor…corrosion on connections, brushes, or old bearings. replace if too bad.
Could be corrosion within the switch or the plug on the switch. ( switch can be worn out inside and need replaced. use jumper wire to replicate switch ‘on’ to test.)
Could be corrosion on the plug on the resistor.
Could be, like my 92 Explorer, ingested leaves into the chamber where the resistor lives and made a short circuit.
Un-plug, clean, and re-plug connections.
Remove reistor and clean out chamber. ( hood open, housing with fan motor and resistor is on paseenger side firewall.)
Use electrical contact cleaner in switch.
Fan motor can be tested with 12v direct to plug for high speed.
Thank You for your help on this …MHO7505