Blower motor problem

chevrolet
blazer

#1

1998 Blazer

The blower motor stopped working
I checked all the fuses, all are ok.
,I turned the blower on high (number 4 setting) I checked for voltage at the blower motor wire harness connector and there was nothing.

I checked for voltage at the blower relay wire harness connector and there was 12 volts on one of the orange wires.

I replaced the relay and still no power at the blower motor and still have power on the orange wire at the blower relay.
I think on high speed the blower bypasses the fan speed resistors and is feed right from the relay.

so, what am I looking at here, a broken wire between the relay and the motor?
or a broken blower control switch on the dash?
or a broken fan speed resistor?


#2

I think you need to look at the variable resistor. Behind the glove box maybe.


#3

That resistor network might be mounted on the blower motor housing on a small panel with two screws. I have had problems with those in the past. Yes, normally the resistor(s) will burn out and it will still run on high, but not always. You should be able to access the motors wires inside there, and can try jumper wires to hook it straight to 12 volts to make sure the motor is ok, then back trace from there.


#4

yes, I saw where the resisters are located, they are under the hood inside the plastic heater duct near the blower motor.
The blower doesnt work on any speed setting thats why i thought it probably wasnt the resisters.one resisiter for each speed setting so I didnt think they would all go bad at the same time.

I dont have the blazer here,its my daughters blazer, the next time she comes by im going to check the 2 wires going from the blower motor to the relay. Ill check the OHM`s on the resisters too.


#5

On my 1978 Oldsmobile, the relay bypassed the resistors and the full 12 volts was applied to the blower motor. I lost the high speed to the motor. I traced it down to a connector that hadn’t been completely pushed together at the factory.


#6

Sorry, I didn’t mean to imply that. There could be a bad/loose connection, as @Triedaq pointed out, or a burnt spot going to/from the network not allowing voltage to the motor.


#7

We still have a few Blazers and Jimmys in our fleet, and I thought I’d add something, in regards to the blower

On a few of them, the connections at the underhood fuse box itself were all burnt up, to the point of having to bypass the fuse box, and route new wires externally

You will NOT see this until you lift up the fuse box and check from underneath. In my case, the only part that was burnt was the one associated with the blower

Somebody skilled and with access to the factory wiring diagram should be able to determine if this is the case


#8

Check for voltage at relay on the red wire. That should have voltage all the time.

Check for continuity on the purple wire between the relay and the blower motor.

Check for continuity at the black wire at the blower motor and ground.

Tester


#9

I unpluged the wire connector from the relay and checked:
red wire has voltage at all times
purple wire has continuity from the motor to the relay
black wire has continuity from the motor to the relay

Then it started raining so tomorrow i`m going to check the orange wire for voltage with the key in run position and the fan speed on high.
going to check the voltage on the dark blue wire with the key in run position and the fan speed at1, then at 2, then at 3

I doubled checked 3 fuses by removing them and visually checking them,they are all good.

im starting to think its the switch on the dash but i`m going to continue working my way back from the motor to the switch.

The last thing ill do is unplug the wire connector from the back of the switch and use a jumper wire to see if the motor runs.Im saving that for last because i hate removing dash panels.


#10

One way to determine if a bad (high ohm) connection somewhere upstream of the blower motor is the problem, disconnect the motor. Do you now have voltage on the car side of that connector? If so, you’re probably looking at a bad connection somewhere between the battery and the blower motor. Most likely where db4690 described above.

It’s possible that the motor itself is shorted out too. You could test it by removing it from the car and using jumper wires to power it up directly from the battery. Only do this briefly, and only if you know the blower motor is designed to work on 12 volts DC. Good idea to used a properly fused jumper wire too.

From what you and everyone above says, my guess you have a burned connection somewhere. That’s a pretty common problem for things like blower motors, fuel pumps, & other electrical stuff that uses a lot of current. I had that problem on my VW Rabbit for the fuel pump power. The connection at the fuel pump relay plate was burned out, and I had to rig up a bypass wire.


#11

I connected the motor directly to the battery using jumpers and the motor works.
i removed the dash switch and checked for voltage at the switch wire harness plug (with the vehicle running) and there`s no voltage.
I checked all the fuses again with a OHM meter and they are all good…

I OHM`ed the pins on the switch and it has continuity in all speed settings, so that rules out the switch.

so now I guess i need to find which wire on the switch plug is suppose to have power and find out why it doesn`t.

It seems like a fuse is blown but ive checked all the fuses 3 times. maybe theres a fusible link for the blower motor?


#12

no there isn`t any voltage on the motor connector even with the vehicle running and the fan turned on.


#13

I found the problem

It was the knob that changes where the air comes out, defrost,floor,vent etc.
The farthest position to the left of the airflow position switch turns on the A/C I was going to turn it to A/C to see if the blower worked with the A/C on but the knob fell off in my hand,I used pliers to turn the knob stem and as soon as i turned it just a little the blower came on.
even though the broken knob was pointing to defrost the switch was actually between two settings.
I ordered a new knob on E-bay
mystery solved and I learned something new.

maybe they made it like that because the vacuum that moves the airflow position door isn`t strong enough to move the door if the blower is running and blowing air through the air duct?
so, each time you turn the knob to change airflow position the blower momentarily stops allowing the door to move?

I can`t think of any other reason why they would route the blower switch power through the air flow position switch.

anyhow, thanks for all the help guys.


#14

For the future . . .

those kind of knobs are usually available in Pep Boys, in the self-help section

That section only has knobs, buttons, caps, and other miscellaneous hardware

The knobs are usually sold under the Dorman name


#15

Glad you got it working again OP. Good for you.