My 07 Impala stopped blowing air so I got a new blower motor. I take the old one out, connect the plug to the new one and nothing. I took a multi meter and connected it’s leads to the plug that goes to the blower motor to see if it’s getting power. As I turned the fan up and down, the meter also went up and down. I’m assuming it’s getting power. Since the meter went up and down along with the fan speed dial, I’m assuming the resistor is working. Next I connect the new blower motor plug with some wires directly to the car battery to make sure the it’s not defective. The blower motor seemed to work fine. What is my next step in troubleshooting this? Thanks in advance.
The meter went up and down between what and what? In other words, what was the lowest DC voltage reading, and what was the highest? If it’s going from like 3-4V (low) to 12V (high), then that’s normal. But if it’s going from something like .3-4V to 1.2V - then you’re dead in the water and probably need a new switch / control head and/or have a wiring problem.
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The blower motor control processor (resistor block) probably isn’t grounding the circuit so the blower motor isn’t able to operate.
Tester
Several pins on the connector to the resistor are inadequate for the current they have to handle. The wires are large enough, they are larger than the wires to the other pins, but the pins themselves overheat and melt the body of the connector. You can buy a replacement connector, but those have smaller wires on the high current circuits. They will work but I can’t say for how long.
Anything close to the 17 years the first set of pins lasted should be OK.
True, for a while anyway. I replaced the connector on my 07 Silverado about 3 years ago (about 250k) and it is still working, but I don’t expect that it will last another 250k, but then I don’t expect the truck to either.
Yeah, just about any time I replaced something on my cars they didn’t last as long and the OEM parts.
I presume you have the multi-meter controls set on DC volts / 20 volt full scale. @cigroller 's post above asks you provide the actual voltages measured for each speed setting. You’ll get better advice here if you supply that info. Beyond that you’ll have to also measure the voltage directly at the motor , not just at the connector. The connector could have a high resistance and that would cause the voltage directly at the motor to be much less than at the connector. Frustrating I know, but I expect this is diy’er fixable. Hopefully it is just the connector. My Corolla’s blower stopped working on the low speed setting 30 years ago … lol … My solution, I just use the medium & high speeds.
This will tell you that the motor is getting voltage but it says nothing about the CURRENT being supplied to the motor. A single poor, tarnished connection can show battery voltage at the plug with no load, but provide practically no current when you turn the motor on.
The correct way to measure this is to measure the voltage at the plug WHILE TURNING THE MOTOR ON AT ITS VARIOUS SPEEDS. If you still read battery voltage at all selections your motor is bad. If the voltage drops substantially when you turn the motor on you have a wiring/connection problem, or a failed switch.
I’ve been through a similar repair on my latest TB. I made a post about my failure analysis of the controller on this site. In that case, the updated blower motor controller also comes with a new replacement pigtail. I was curious about that so did some digging. The male pins on the controller are the same as its predecessor (same spacing, pin dimension and plating material type). The new pigtail connector has female pin sockets with a different contact scheme. They have the same contact patch area but upon closer inspection (and looking up the pin specs) have an improved spring mechanism.
The reason the connectors in the TB deform later in their life is due to heating. In this case, the heating is caused by deteriorating connection rather than inadequate pin size for the current.
Contact resistance can increase over time due to oxidation or other types of corrosion. Another failure mechanism is stress relaxation. The spring loses force over time. The contact resistance goes up and that causes heating. It’s a spiraling problem that continues to get worse until it eventually fails.
Of course, a failing blower motor can draw a lot more current than one that is operating normally as well. In my case, the blower motor was fine and like yours, all is well for a couple years since the repair.
If the resistor block wasn’t grounding, the OP wouldn’t be getting a voltage reading across the pins on the connector. It may not be a strong ground, but it’s getting a ground.
How do you suggest the OP turns the motor on when it’s not working?
You would get voltage if the ground lead for the meter is connected to something metal under the dash and not to the ground on the plug.
Tester
With the speed selector switch, how else?
Whether the motor is working or not, the circuit is “on”, power should be applied.
Or the fan-cage might be obstructed with leaves & twigs. That could cause an over-current problem.
Leaves & twigs normally make a lot of noise, along with paper products that obstruct the blower motor…
Yes, but why would you ever connect your negative lead like that? You need to know if the resistor block is providing the ground and to test that you need to connect the negative lead on the connector pin going to the resistor block (B on the wiring diagram you posted). If you connect the negative lead to something metal under the dash, all you know is that the motor gets power IF there’s a ground which you just provided. You will chase your tail if you think the motor is getting power when you provide the ground.
My point was just to say that because the OP has voltage when measured across the connector pins, the resistor block is ground.
Just because you turn the fan switch on doesn’t mean power is applied. If the circuit has no ground, there will be no power at the motor when the fan speed switch is on if you connect your multimeter across the connector pins. If you connect your meter to a different ground, you are providing the ground that the circuit doesn’t have access to and show that you have voltage when you don’t. The OP had voltage when measured across the connector pins at various fan speed settings and assumed the motor was bad, and replaced it. The new one doesn’t work when plugged in but does work when connected directly to 12V. I’m betting the original motor wasn’t bad but the OP hasn’t been back to confirm or deny that.
You asked “How do you suggest the OP turns the motor on when it’s not working”.
Now you’ve changed your position. Why?
You said “Just because you turn the fan switch on doesn’t mean power is applied.”. Wrong again. Power is, in, fact, applied. It just has no return path, so there will be no current flow.
And nobody cares what you’re betting. I simply suggested a technique for how the OP could find his problem.
When I did a stint working on med duty trucks, I had a GM Topkick that the blower motor wasn’t working, I got lazy and grabbed the old trusty test light, grabbed a chassis ground and had power to the blower motor (and yes the snap on test light was very dim on low and got brighter as the switch/resistor applied more power), installed a new blower motor and still nothing, oops, took me a minute to figure out that the fuse box was full of circuit breakers instead of fuses, and they were on the ground side of the blower motor, changed out the circuit breaker and blower motor worked again…
Even though it had good power, the power did not make a complete circuit due to no ground from the dead circuit breaker… 