Blower motor only works on blast

LeakySeals

LeakySeals

Joined
Feb 18, 2011
Messages
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Location
Hudson, NH
I need help. The blower motor on our 2005 Chevrolet Classic will only work on level 5, the max setting. What I’ve done so far:

1) Replace blower motor resistor
2) Replace control panel
3) Replace blower motor

None of these repairs solved the problem. Assumption is the relay is good because it’s running on 5. It has a new blower motor resistor from AutoZone. Control panel and blower motor were used OEM that came from eBay junkyards.

What should I do next? What else controls the lower speeds?
 
You might try unplug the panel from the resister right at the resister. The control panel controls the motor speed by changing the voltage to the resister through the signal wire. There should be three wires. One is ground. One is the variable voltage signal wire and the third is the power wire.

Have someone change the fan speed on the control while you measure the voltage between the signal wire and ground. The voltage should start at about 5 volts at the lowest setting to close to 12 volts at the highest reading.

The highest fan speed actually bypasses the resister so if only the highest speed works, and you are getting the proper signal you might try another resister. Failing that try another fan unfortunately.

Let’s us know what you find.
 
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Voltage without load isn't the greatest test, put a brake light bulb or something on there and see if it dims and brightens.

Otherwise, it's another vote for the pins not making contact.
 
Since the blower is getting a constant 12 volts determining the source using a schematic, if available, would be the next step. Sounds like a back feed perhaps from the BCM. Would also check grounds.
 
Snagglefoot said:
You might try unplug the panel from the resister right at the resister. The control panel controls the motor speed by changing the voltage to the resister through the signal wire. There should be three wires. One is ground. One is the variable voltage signal wire and the third is the power wire.

Have someone change the fan speed on the control while you measure the voltage between the signal wire and ground. The voltage should start at about 5 volts at the lowest setting to close to 12 volts at the highest reading.

The highest fan speed actually bypasses the resister so if only the highest speed works, and you are getting the proper signal you might try another resister. Failing that try another fan unfortunately.

Let’s us know what you find.
Click to expand...
^ what he said - except I can't see it being the fan since thats nothing more than a simple brushed DC motor.

So likely resistor. Then maybe the control switch. Then wiring / pins. Ohm meter is your friend - or as mentioned a bulb soldered to a couple leads is even better
 
SC Maintenance said:
^ what he said - except I can't see it being the fan since thats nothing more than a simple brushed DC motor.

So likely resistor. Then maybe the control switch. Then wiring / pins. Ohm meter is your friend - or as mentioned a bulb soldered to a couple leads is even better
Click to expand...
I just did one. It was the fan, ( after I already put in a new resister). At the top speed it ran fine, but at lower speeds it was hesitant or very weak). YRMV.
 
Snagglefoot said:
I just did one. It was the fan, ( after I already put in a new resister). At the top speed it ran fine, but at lower speeds it was hesitant or very weak). YRMV.
Click to expand...
Weak vs not spinning at all is different. A brushed DC motor you put voltage to it and it should turn. Bad brushes or dirty windings can certainly limit performance, but as all the resistor does - as you pointed out - is vary the voltage. So if it spins well at 12V, then it should spin some at 10V. If it spins none at the first lower setting for example, I would expect something other than the motor.

Of course I haven't seen everything - so maybe I am being educated.
 
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LeakySeals said:
I need help. The blower motor on our 2005 Chevrolet Classic will only work on level 5, the max setting. What I’ve done so far:

1) Replace blower motor resistor
2) Replace control panel
3) Replace blower motor

None of these repairs solved the problem. Assumption is the relay is good because it’s running on 5. It has a new blower motor resistor from AutoZone. Control panel and blower motor were used OEM that came from eBay junkyards.

What should I do next? What else controls the lower speeds?
Click to expand...
OP, is your system equipped with a manual fan switch or is it an automatic temperature controlled unit. My comments were for an automatic system with three wires to the resister and two wires out from the resister to the motor.

On a manual system there are several wires going to the resister unit. The voltage will be the same but will appear at different pins as you adjust the fan control. Hope that helps.
 
Snagglefoot said:
OP, is your system equipped with a manual fan switch or is it an automatic temperature controlled unit. My comments were for an automatic system with three wires to the resister and two wires out from the resister to the motor.

On a manual system there are several wires going to the resister unit. The voltage will be the same but will appear at different pins as you adjust the fan control. Hope that helps.
Click to expand...
Yes, it’s manual. I have the old one. Some pics.
 

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Snagglefoot said:
If you already changed the fan and the resister assembly, I definitely would suspect that controller with the computer card. Hate to throw the parts canon at it.
Click to expand...
It’s number two on the list. That’s the old one I’m showing you. Replacement was a junkyard control panel, but same problem as the original
 
If the board is bad you can often see it - in the form of a burned, melted or discolored component or a broken trace. Maybe post high res photo of each side of the board so maybe some electronic repair guru's can look. I imagine there are a few around here.

How does the board connect to the resistor - is it a normal plug that is wired or a ribbon cable or?
 
Did you check all your fuses at the fuses for power on both sides? Just because high works there are often one or two separate fuses for the lower speeds. Check a fuse diagram and check for power both sides on all fuses listed.
 
I know a lot of GMC and Chevy trucks the wire harness used to burn up going to the resistor too.
Some higher end replacement boards/resistors used to come with a new harness pig tail too.
 
Snagglefoot said:
OP, is your system equipped with a manual fan switch or is it an automatic temperature controlled unit. My comments were for an automatic system with three wires to the resister and two wires out from the resister to the motor.

On a manual system there are several wires going to the resister unit. The voltage will be the same but will appear at different pins as you adjust the fan control. Hope that helps.
Click to expand...
^^^^^^^^^^^^^^^^
This
Something like this, but this is for a 2001 Grand Prix. Your wire colors may be the same or different colors, but same Idea!
On the GP system, there is a separate 30 Amp fuse for Hi Blower and a separate relay for Hi.
And a FUSE FOR THE TEMP SPEED CONTROLER AND A FUSE FOR THE RESISTOR BOARD.
Thread starter said 2) Yes, it’s manual. I have the old one. Some pics.
Replace control panel.............................Happens, but these rarely go bad.

Grand Prix Blower.png
 
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