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Old 02-09-2013, 11:56 PM
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Heater Question

I have a 72 Chevelle. The heater fan doesnt work I guess. I flip the switch to high, low, medium.....nothing. I feel a little heat coming out of the defroster, but nothing powerful. Any suggestions other then the blower motor?
Anyway to check wiring or fuses?

Thanks,
Mike

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Old 02-10-2013, 06:17 AM
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If you can get to the connector for the blower motor, just put a test light on it and see if you have voltage when you switch on the heater. If you have voltage and the motor does not move, you need a motor. Good news - they are not expensive.

No voltage at connector - you may have a bad blower resistor pack or a bad dash switch. However, usually when the resistors fail you still have high speed. The resistor is mounted inside the heater plenum near the motor, and it will have 3-4 wires.
How it works: High speed is a direct connect to full 12 volts. For lower speeds the resistor pack switches in combinations of resistors. The resistors are ceramic and often break when they get old.

If your car has A/C there may be a separately fused 12 volt line for the high speed blower relay. The power line often runs across the back of the firewall, and it has an inline fuse holder.

Bruce
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Old 02-10-2013, 06:33 AM
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power and ground.

I just went thru that with my ranger, corroded connections at the relay. On some wiring systems, the ground is switched thru the resistors. .I had power at the blower but it didn't run. to test your motor it's best to Jumper feed 12 V and use a ground wire.
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Old 02-10-2013, 08:01 AM
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Quote:
Originally Posted by 75gmck25 View Post
If you can get to the connector for the blower motor, just put a test light on it and see if you have voltage when you switch on the heater. If you have voltage and the motor does not move, you need a motor. Good news - they are not expensive.

No voltage at connector - you may have a bad blower resistor pack or a bad dash switch. However, usually when the resistors fail you still have high speed. The resistor is mounted inside the heater plenum near the motor, and it will have 3-4 wires.
How it works: High speed is a direct connect to full 12 volts. For lower speeds the resistor pack switches in combinations of resistors. The resistors are ceramic and often break when they get old.

If your car has A/C there may be a separately fused 12 volt line for the high speed blower relay. The power line often runs across the back of the firewall, and it has an inline fuse holder.

Bruce
Also check the all important ground.
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Old 02-10-2013, 06:02 PM
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X2 on the ground, had one that had 12v to motor, motor wouldn't run....... jumper the motor and it runs...... ended up being a dirty ground..... I found this out by touching a good ground wire to the motor body and it ran....... cleaned the mounting points and it was fixed.
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