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Need help with cab AC/Heater blower not working

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Old 10-09-2010, 11:05 AM
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Need help with cab AC/Heater blower not working

I've researched my problem on FTE and read threads on issues with the vacuum system creating ESOF shifting issues along with the cab air diverter not working.

I don't think I have the same issue.

My heater/ac fan (blower) sometimes does not run at all, at any speed setting, when the truck is first started. Then when I drive for a while, all of a sudden the air will come on and everything is fine. It will work for a long time, through many truck starts without issue. Then again, one day it won't work again.

I'm wondering if there is a relay sticking that needs replacing or at the worst, a new fan motor.

My air diverter and ESOF are working fine and I have no vacuum leaks that I can find. I can hear the air diverter moving and the vacuum pump working without the truck running but the key on.

Can anyone give me ideas for trouble shooting this problem or experienced this before?

Any help appreciated.

See my sig for truck model.

Thanks in advance.
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Old 10-09-2010, 11:49 AM
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One of the things I would check is the electrical connections on the fan. If the connection is not good, then maybe what is happening is when the truck heats up, it warms the connection, and causes it to make. Could also be a connection inside the fan itself. If it's inside the fan then your easiest solution is to replace the fan. If you have a multi-meter, throw it in your truck, and next time it happens, hop out and take a resistance (Ohm) reading on the leads to the fan. If the resistance is way high, then the problem is in the fan itself.

Or it could be something else. That's what I'd check, but it's probably cause I'm an electrician.
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Old 10-09-2010, 11:56 AM
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Thanks. I have a multimeter and can check that. I'll let you know what I find. What would be a "normal" resistance reading if there isn't a problem.
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Old 10-09-2010, 12:02 PM
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I don't know what normal would be specifically, but if it's bad, the reading will be extremely high or some form of "infinity" on a digital multi-meter. You could look at the fan and on the motor it should say how many amps it draws. If you divide the volts (12) by the amps, that should give you a good idea of what the ohms should be.

*edit* If the reading is a lot lower than what you calculated by dividing volts by amps, it's probably still good. Motors have much lower resistance with no power than they do once you put power to them.
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Old 10-09-2010, 12:33 PM
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Thanks for the advice. It was the connection. I should have thought of that too.

I unplugged it and plugged it back in and on it came. The resistance I think is good at 0.7 ohms.
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Old 10-09-2010, 12:36 PM
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Yup. Sounds good. Glad to help.
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