Blower motor resistor [Archive] - Chevy Malibu Forum: Chevrolet Malibu Forums

: Blower motor resistor


Jheuermann
07-17-2010, 06:39 PM
Hello all,
New to the forum so thanks in advance for any help. I have a 2005 Malibu ls with manual ac controls. I believe the resistor is bad, but before I purchase a new one, I wanted to test this one. Does anyone know of a test to confirm this. I have multimeter and volt light. Just want to make sure it's not the switch or the motor itself. Thanks for any help!!!

Starship
07-17-2010, 07:04 PM
If you need the manual A/C circuit wiring diagrams, check out http://cid-54465800aad91b49.office.live.com/self.aspx/pub/va200296.pdf and http://cid-54465800aad91b49.office.live.com/self.aspx/pub/va200297.pdf.

DrivenDaily
07-17-2010, 07:43 PM
There should be one wire going to the motor and the rest are from the speed control. Disconnect the resistor pack, plug in only the motor wire, and then use a heavy wire to put +12V to each of the other terminals. The blower should turn at different speeds as you touch each one. If it doesn't, but turns at full speed when you put voltage to the motor wire, then the resistor pack has failed.

Jheuermann
07-18-2010, 06:10 PM
Thanks for the info. There Is a purple wire and a black wire going to the blower motor. I'm assuming the black is ground and purple is hot? On the resistor there Is 5 terminals. Ground, signal, power, M-, and M+. There is power to the resistor but no power at the blower motor terminal. Does this prove the resistor bad? By the way, I hot-wired the blower motor and it did work.

DrivenDaily
07-18-2010, 07:03 PM
Thanks for the info.

1. There Is a purple wire and a black wire going to the blower motor. I'm assuming the black is ground and purple is hot?

2. On the resistor there Is 5 terminals. Ground, signal, power, M-, and M+. There is power to the resistor but no power at the blower motor terminal. Does this prove the resistor bad?

3. By the way, I hot-wired the blower motor and it did work.

(Edited for answering.)

First, thanks to Starship for his kindness in providing the invaluable schematic for your car! I don't know where you find them, but keep up the great work!

To answer your questions:

1. The purple wire supplies positive voltages to the motor and the black provides the ground conneciton.

2. The resistor you need to pay attention to, per the 20296 schematic (on the bottom), has only 4 terminals. They're Low, Medium 1, Medium 2, and Out-to-Motor. You put +12V to any one of the first three and the output terminal voltage changes, making the fan spin at different speeds. If you have a 5-terminal resistor then you either have a different setup or you're looking at the wrong component (see #3 below).

3. It's good that you know that your motor runs. Look on the next schematic, 20297, up at the top. You'll see a relay for high speed operation and below it the motor. The relay has five terminals. (Is this what you're referring to as a resistor? It appears so!) When the blower is being operated at other-than-high speed the voltage flows through the two terminals that are electrically referred to as Common and Normally Closed (NC), with the varying speed on NC and the motor on Com. When you turn the control to High, it tells the relay coil to pull the Normally Open (NO) contacts closed, forcing the motor to spin at full battery voltage, or high speed. If you can turn the control to High and it runs on high, but turning it to a lower speed results in no blower, then you have one of the following issues:

a. The NC contact or terminal is damaged. To fix it, replace the relay.
b. The speed resistor is burned out, or one or more terminals are damaged. To fix it, replace the resistor.


To determine if the relay is faulty, provide +12V to the dark blue wire on the resistor pack or the relay. If the blower spins at high speed then the relay is fine - your issue is the resistor pack, the wiring to it, or possibly the fan speed control in the dash.

To determine if the resistor pack is faulty, leave it plugged in, turn the speed control to OFF, and put +12V to each terminal. If the blower spins at varying speeds then the resistor is good; if not, it's bad - replace it.

To determine if the dash-mounted speed control is faulty, turn it to Low and check the Yellow wire for +12V. If it has +12V, Low is good. Turn it to Medium 1 and check the Tan wire the same way, then turn it to Medium 2 and check the Lt Blue wire the same way. If you get +12V at the resistor terminals but nothing at the terminal with the Dark Blue wire then the speed control is good but the resistor needs replaced.

********************
For those not that familiar with relays, think of them as power steering for electricity. A small amount of power is all that is needed to cause a large amount of power to flow to a motor, or a light, or whatever. This keeps the dash nice and tidy because it only needs to have small wires, instead of the "old days" when it needed big wires to do the same job. In this thread, the relay is near the motor, keeping the large wires short and away from the center of the dash where there's less room. Plus it keeps the heat behind the dash to a minimum.

Jheuermann
07-18-2010, 07:14 PM
Thanks Driven for the very detailed info. I assumed the component was the resistor because it was right next to blower motor. It is actually mounted in the blower motor plenum. I will take your info and a test light tomorrow and perform these tests. I will let you know my results. Thanks again