1997 GMC C1500 fan

1997 GMC C1500
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FSTEINER
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Heater problem
1997 GMC C1500 6 cyl Two Wheel Drive Automatic

Heater fain can not be turned off. It runs at full speed upon starting the truck and does not repsond to the switch adjustments. It performed erratic for a day or two prior to this event.
Jan 4, 2009 at 8:29 PM
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JDL
  • ✓Experienced Mechanic
  • 16,098 POSTS
There is a high speed relay for that, but, the fuse for the high speed circuit is hot all the time. If the relay was stuck on high speed, the fan would run, even with the key turned off. I can't tell if the motor is running high speed or lower

The fuse circuit for the lower speeds, is ignition feed, goes hot when you turn on the key.

The voltage wire from the blower motor goes to the relay, you might be able to do some testing at the connector for the relay. You might remove your glove-box and see if you can find anything?
Jan 5, 2009 at 4:39 AM
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