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post #1 of (permalink) Old 05-06-2019 Thread Starter
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new to the forum 2005 heater fan question

I have read a few posts here and other places about the problem with the heater fan and resister. I made a connection between the right cigarette lighter socket and the heater motor. Plug it in and the motor runs on high. Everything on the heater console works fine. Temp changes, AC works, inside and outside air works fine.
Before I go any farther I had water in the passenger foot area any time the car was parked on the street. I removed and replaced the cabin air filter. It was a horrible mess. There is a rubber / foam piece that goes between the air filter and the windshield. It looks like it's main purpose is to direct any water away from the filter. It had moved to the opposite side of the filter and was now a dam channeling the water into the filter. And of course it came down through the blower motor to the floor. It was an easy fix and easy to check on. I mention it because the water was in the fan and in the area of the resistor.
My problems started like many. The fan would quit and if you reached down and kicked it it would start up again. Then that didn't work. Then I found out if I crossed a rough set of tracks at 35 mph it would work for several days. Then that quit working. Now it's winter and a very cold one. Below zero the inside of the windshield will frost over in the first block without a heater to defrost the inside of the windshield. So that's why I did the easy fix with the cigarette lighter. But you have to remember to unplug the lighter socket end or the fan when you shut the car off or the fan will keep on running and you'll come back to a dead battery.
I installed a new resister and it did nothing. I checked the ground every way I could think using the cigarette lighter as my ground point.
I checked the fuse in the panel by the driver's side door and it was fine. Both the fuse and the cigarette lighter socket show about 14.5 to 14.6 volts with the engine running.
The power wire to the 5 pin resistor plug (red wire in the middle) is always hot but it only shows about 11.9 volts and it seems to wander a little higher and lower, never staying rock solid. If I check voltages from pin one to pin 2 on the off position (Which GM claims is a one of the 10 speeds) it wanders all over the place but is very low. #2 speed is 126.1 mV, #3 is 130.0, #4 is 135.4, #5 is 140.0, #6 is 145.9, #7 is 151.9, #8 is 159.7, #9 is 168.4, and #10 (what a joke) is 175.6 mV. These are the readings from the control box to the resistor. And when I plug all of this into the resistor NOTHING comes out to make the fan run. And I tried a new resistor with no changes.
Someone said there are fuses and modules under the hood. I found 2 25 amp fuses marked fan and they look and tested good. Above them are 3 modules marked FAN CONT #3 , 2, and 1. #'s 3 and 1 are marked 3604 and are a light blue and #2 is marked 3602 and is black. I don't know if they are used for the heater system or how to check them to see if they are good.

ANYONE out there with a notion of what's up. In a post somewhere it said the wires running above the ashtray could be bad, but I'm getting voltage to the 5 pin connector. The ashtray is out and I've moved them every which way I can with no changes.
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post #2 of (permalink) Old 05-06-2019 Thread Starter
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Does anyone know which wire going to the 5 pin connector to the fan motor resistor is the ground wire?
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Originally Posted by IowaFarmBoy View Post
Does anyone know which wire going to the 5 pin connector to the fan motor resistor is the ground wire?
Pin A, black, is ground according to the attached drawing. The wire at pin D is also black, so be careful you have the right one.

HTH.

Doug

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If your socket set is all the same brand, you might be a city slicker.

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2 grounds, not one



There are 2 grounds on the 5 pin plug. A and D. I can get voltage on A to C where C is always hot. Since they are both grounds I should get continuity between A and D, or between A or D to the cigarette lighter receptacle, which I can't.
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Quote:
Originally Posted by IowaFarmBoy View Post

There are 2 grounds on the 5 pin plug. A and D. I can get voltage on A to C where C is always hot. Since they are both grounds I should get continuity between A and D, or between A or D to the cigarette lighter receptacle, which I can't.
No. Look again. At first glance, it appears D is at GND, but it's not, at least not always

E supplies power to the motor - it's the high side to the motor.

D is the low side of the motor. The control raises and lowers the voltage at D which affects the current flowing thru the motor, out E and back into D.

When D is high, the voltage drop from E to D is small and the motor spins slowly. When D is low, say at GND, then the full voltage at E is across the motor and it's turning its fastest speed.

I wonder if the motor isn't going bad. If the bearings are failing, they usually squeal quite annoyingly. But that's not guaranteed. If there's too much rotational resistance in the motor, on high settings, it may have enough torque to overcome that and start running. But at low settings, it may stall.

To test things, with the motor connected, you want to measure the voltage between E and D, and see that it increases as you increase the fan speed setting.

Guessing, I would expect to see something like 4-6V on the motor at the low speed setting. (And 12V on high.)

HTH.

Doug

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If your socket set is all the same brand, you might be a city slicker.

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