Question about 1989 Jeep Comanche

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Ac/Heater pulling too much voltage when used

When using the ac/heater on my '89 comanche I6, the in dash voltage meter drops below 12 volts when running it eventually drains the battery until it's too weak to start the truck. It doesn't blow the fuse and still works. It only draws when the unit is turned on. Any suggestions?

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  • shane_agnew Jan 19, 2009

    The alternator checked out ok.

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This actually could be a few issues. you'll need to check a few things.

First the simplest is that the Blower Fan is indeed faulty and drawing too much current, if that's the case that blower motor should be very hot when run. If so its likely the culprit.

But you could also have a faulty voltage regulator. this is built into the alternator and can be easily tested at most major parts stores for free(some while in the vehicle). I suspect this may be the case because you are not blowing fuses or breakers and the alternator inst keeping up with the load.

The other could be a short such as an abrasion on wiring to the blower or compressor unit.

And finally, double check that there is a good ground wire or braid between the engine and the Body. this could cause all kinds of charging and electrical anomalies if there is a bad block to body ground.

Posted on Jan 19, 2009

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Get your Alternator Checked out. This should not happen unless it is bad.

Posted on Jan 19, 2009

  • Travis Humphries
    Travis Humphries Jan 19, 2009

    Then you have a Wire in the Harness that is Grounding somewhere inside the Dash. Not easy to find But, Would cause this Problem. Possibly a Ground wire.

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