04' Grand AM AC


#1

Think I’ve got this narrowed down but I am unsure…

Gf bought an 04’ Pontiac Grand. AC worked fine on the test drive then after a few weeks the AC stopped blowing air. I can feel the compressor is working and the air is being conditioned but the blower motor does not turn on. I’ve tried using all the speeds and none of them work. I do not believe the controls are to blame but rather either A.) resister or B.) connector(s) or C.) blown blower motor.

Have not had any experience with the blower motors and resisters, any advice?


#2

First check if the blower motor fuse is blown.

If the fuse is good, then turn the ignition on, turn the blower speed to high, and then reach under the passenger side of the dash and tap on the blower motor with the handle of a screwdriver. If the blower starts working replace the blower motor.

Tester


#3

Fuse is good tapping the motor did nothing. Resistor or connectors then?


#4

Do you have a voltmeter or test light? I’d check for 12V at the motor before tearing into something else. Motor failure isn’t always as easy to determine with the tap method.


#5

If you’re not getting any speeds from the blower, then I feel the problem is with the vent control module.

http://www.lkqonline.com/custom/product_detail.aspx?item_guid=95cb53d0-9714-4ae6-bec3-524ac25cd707

Replaced a few of these on GM vehicles in my day for the same problem.

Tester


#6

If the fuse is good, I’d recommend checking the blower motor and the resister network.

The blower motor will be mounted on the ductwork under the passenger side dash. A Chevy dealer part guy should be happy to print an “exploded view” drawing of its installation to assist you in removing it. He can also provide you with a schematic and wiring diagram for the blower.

The blower motor will simply need to be tested. You can do this on the bench, or mounted in the ductwork using pin probes and a battery. I’ve tested them with a 9VDC transistor radio battery and they spin beautifully (if they’re good). I’ve never tried it, but I’m sure a 6VDC lantern battery would work great too, if you have one of those. The motors draw little current, and reducing the applied voltage is how the speed on DC motors is regulated anyway. If it doesn’t spin freely with a 9VDC battery, the motor is bad. Again, I’ve never tried a 6VDC battery but if it didn’t spin with a lantern battery I’d pull it and bench test it.

If you’re a bit conversant with multimeters and schematics, you can test the resistor network, but you may have to pull the controls as well to ensure that it isn’t the controls themselves. If you’re not conversant with a meter and schematic, any auto-electrical specialist shop can check this out for you. I think they’ll be better at this that the average shop.


#7

My question is, how does a 9VDC battery provide enough current to operate a blower motor?

The blower circuit has a 15 amp fuse.

Tester


#8

It does. I’ve used it more than once to bench test blower motors. It works great.
If you doubt me, try it.

As is typical of all fans, including squirrel cage fans, there is a startup spike, but the current draw quickly drops to a low level. If you’re running a trace on a scope of monitoring current on an ammeter, you’ll see the spike. It’s perfectly normal.

By the way, squirrel cage fans are well known for their low draw.


#9

No way!

I use one of those 9 volt memory savers that plug into the cigarette lighter when the battery is disconnected. And if you open the door where it causes the interior lights to come on, it kills that 9 volt battery right then there.

Tester


#10

That’s wonderful to know. If I ever use one to maintain the computer memory, I’ll remember to turn off all the lights.
Too bad you’ve never tried it on a blower fan.


#11

Sounds good. Will be getting the truck off the repair area tomorrow though shes got work all day so chances are won’t get around to digging into the kick panels until Wednesday. Tempted just to pull and bench test the motor and (if I can find diagrams) attempt testing the resister.


#12

Diagrams should be available free of charge at the Chevy dealer’s parts counter. My local Toyota dealer has always been happy to print tech documents for me. They know me pretty well there, because I used to bring my own documents, but since I’ve lost my access to Toyota’s database (since retiring) they’ve been happy to accommodate me.


#13

Good thing, going to the dealership tomorrow to pickup my connectors tomorrow. Good guys don’t mind spending the extra on some parts.


#14

“If you’re not conversant with a meter and schematic, any auto-electrical specialist shop can check this out for you. I think they’ll be better at this that the average shop.”

If you have the correct wiring diagram and a multimeter, only the most incompetent and/or inexperienced mechanic should have difficulty diagnosing this problem

I don’t think a specialty shop is necessary to diagnose blower problems


#15

I’ve got college experience for Electrical Systems (PLC, industrial wiring, etc.). With cars just takes some time for myself to be able to transfer and apply the skill to troubleshooting.