Mechanics

THE HEATER BLOWER FOR INSIDE THE CAB IS WORKING AND THEN IT STOPS THIS HAS BEEN HAPPENING FOR THE PAST 6 WEEKS ON AND OFF, PLEASE HLEP

1998 Dodge Truck • 250,000 miles

L put a new heater blower relay in the fuse box under the hood, put did not fix it, please help best james
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Burns
December 18, 2011.



If the power windows and radio quit at the same time, suspect the ignition switch or connector, especially if you use the fan on the highest speed often. I can describe how to repair the switch wiring if the connector is melted.

Caradiodoc
Dec 18, 2011.
The windows work and power windows work all the time best James

Tiny
Burns
Dec 18, 2011.
Dandy. The next best place to start is with measuring the voltages right at the fan motor when it stops running. You should find 12 volts on the dark green wire. If it's missing, we have to look at why the relay isn't turning on. Next, you should see 0 volts on the black / tan wire when it's still plugged in, and the switch is set to the fasted speed, and you should see progressively higher voltages as you reduce the speed. If you always have 0 volts on any speed when the motor quits running, the brushes are worn and the motor must be replaced.

If you find the full battery voltage, (12 volts) on the black / tan wire, there is a break in the ground side of the circuit. Further tests will determine if that is in the resistor assembly / connector or the switch assembly.

If the modes also do not switch properly when the fan stops working, suspect the ground wire that both systems have in common.

Caradiodoc
Dec 19, 2011.
Thanks! L will change the resistor

Tiny
Burns
Dec 19, 2011.
Don't just throw random parts at it. The resistor assembly usually has a thermal fuse built in but it will not be intermittent. For intermittent problems, I suppose there could be a loose mechanical connection on one of the wire-wound resistors, but then the motor would still work on the highest speed. The resistor is bypassed on the highest speed.

Caradiodoc
Dec 19, 2011.