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carguyjosh, ASE Certified Technician
Category: Chevy
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Experience:  ASE certified , 16 yrs in field
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1998 Chevy: blow..fuses..the compressor clutch ... Would you

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1998 Chevy K1500 Silverado
Heater fan will not blow .. fuses are good .. so is the relay and because the fan won't turn on even though the light turns on when you push the A/C button it does not engauge the compressor clutch ... Would you suspect the dash control unit?
Good morning.

I would not suspect that the control unit in the dashboard is failing.
The most common cause of a blower motor failure on these trucks is a failing blower motor resistor.

Please let me know if you have a test light or multimeter and I can give you the diagnostic steps to find the source of the problem.

Thanks, Carguyjosh
Customer: replied 7 years ago.
Yes Have both but prefer multimeter.

Okay well lets start testing.
The first thing I would like to have you do is test to verify that the fuse in the underhood relay box is good.

If the fuse is indeed good, I would like you to get to the blower motor. You'll find the blower motor under a trim panel above the passenger seat.
Disconnect the two wire connector and connector multimeter to both wires.
With the key in the on position, check to see if the blower motor has 12 V. If the motor has volts being supplied to it, the motor is at fault.

If the motor does not have 12 V. We will need to gain access to the heater control resistor.
To get access to the resistor if memory serves you will need to pull the glove box. The resistor sits on top of the heater box.
You will find that the blower motor resistor has four wires plugged into it. The wire colors are dark blue, light blue, tan, and yellow.
With the resistor unplugged, key in the on position, turn your blower fan switch onto speed one. Check for power on the yellow wire at the resistor.
If you have power at the yellow wire at the resistor, the fan speed switch is sending signal and we will assume it's good and can at least make the fan run on one speed.

You will find next to the resistor a blower control relay.
With the key in the on position, blower speed set to the first speed I would like you to test for power on the dark blue wire going into the relay.

If you have power on the dark blue wire I would like you to test for power coming out of the relay on the purple wire.

If you find that you have power going into the relay on the dark blue wire but no power coming out on the purple wire, the relay is failed.

Please let me know what you're testing reveals, and I will get back to you as quickly as possible with further answers.
I am at work from 7 AM to 5 PM but do carry a Blackberry so will getyour response as soon as you send it and get back to you as quickly as possible.

Thanks, Josh

carguyjosh and other Chevy Specialists are ready to help you
Customer: replied 7 years ago.
Thank You Thank You ..... I will preform these tests just as soon as it get light here .... and get back with you ....
Customer: replied 7 years ago.
Boy what an easy fix. Once I got under the Dash and over to the Blower Motor. Turns out the purple wire (12 Volts) going to the Blower Motor was loose enough that it had gotten HOT due to increased resistance. Cleaned it up ...Tightened it up with needle nose pliers and BINGO ... Fan works at all speeds and the A/C Compressor cycles now like it's supposed to. Thanks for aiming me in the right direction. I was about to order a controller

Well I'm glad to hear it was such a simple fix.
It's nice when it works out that way..


have a great week. Thanks, Josh