1996 Chevy Astro HVAC blower

CURT SMITH

MEMBER
1996 CHEVROLET ASTRO

Heater problem
1996 Chevy Astro 6 cyl Two Wheel Drive Automatic 245xxx miles

Blower doesn't work, all fusses fine bypass all switches direct route from battery to fan and fans works. Two wire lead to fan shows 12 volt when switch is on low, m1, m2 speeds but when put on high I have no voltage. I checked power on 6 wire plug going into resistor everything powers like it should! Can the fan still be bad or is the hvac module bad?

Thank you for your help!

5 Replies

JDL

MECHANIC
16,098 POSTS

The info I looked at, was for a front blower motor. Did you check the circuits where the fuses plug in, as well as the fuses? The circuit for the fuse in the under hood relay center, is hot all the time. That fuse controls voltage for the switch side of the relay. The other fuse, controls voltage for the coil side of relay when activated plus the feed for the lower speeds The circuit for the fuse in the instrument panel fuse box, goes hot when you turn on the key.

There is a high speed relay, unless the relay is energized, there is no high-speed. When the relay is de-energized, there is continuity with the lower speed circuits.

I have seen blower motors with bad brushes, they would operate intermittently.

Did you check the ground for the blower motor?

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Monday, October 6th, 2008 AT 8:53 AM

CURT SMITH

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3 POSTS

Hi, thanks for the reply.
All the fuses are good and so is the ground, I have not checked the power at the relays but if I'm getting all good readings on the plug at the resistor of the blower motor wouldn't all the relays be good, I'm not very good at measuring ohms and resistance but it seem's that the only problem left is the hvac control module at the dash. When I put a direct line from the battery to the fan it does seem to delay a split second before it goes could it be that my fan is just bad! But why would it turn when hooked up like this?

Thanks again for your help!

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Monday, October 6th, 2008 AT 12:48 PM

JDL

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16,098 POSTS

Did you do any testing at the blower connector? Take the connector loose. Purple wire is voltage, black is ground. You don't have to start the vehicle, turn on the key, activate the hvac control, try the different speeds, see if there is good voltage on the purple wire, if there is and the ground is good, then I suspect the blower motor.

I believe you said there was no voltage at the motor with the high speed setting, how about the other settings. The purple wire at the motor.

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Tuesday, October 7th, 2008 AT 12:46 PM

CURT SMITH

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That was the first place I started, I had power at all of the fan speeds except the high setting. I have changed the hvac module in the dash which I figured was bad and that has fixed the problem.
Thanks for helping!

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Tuesday, October 7th, 2008 AT 5:40 PM

JDL

MECHANIC
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I'm glad you got it.

The circuits you checked, that had good voltage, that voltage comes FROM the control module. The fan should have been running. The voltage to the resistor comes from the control module. Maybe it was low voltage or an intermittent issue. There is no resistor for the high speed circuit. It is interesting.

Just to add, I shouldn't have used the word, ( control module), even though, that's how the wiring diagram labeled it. Control module usually means a computer module, I don't believe your hvac is computer controlled.

I don't know what you replaced, unless it was the blower motor speed switch?