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2007 Toyota Corolla AC Blower Issues

I posted the following in January 2016 and am including it in this new post to provide past history:

“The air conditioning blower motor stopped working this past summer (worst timing ever). I took it out, put it back in, and it worked again for a day before dying for good. So, I ordered a new one and replaced it. The replacement was working fine for about 5 months, but it then began exhibiting the same problem as the original: it wouldn’t come on until after I’d been driving for a while. The new unit never made any unusual noises while running (the old one got noisy just before I replaced it), but now it isn’t coming on at all. I find it hard to believe that the replacement blower motor has failed after only 5 months. What else should I check?”

The problem has intermittently resolved itself for a few weeks or months only to eventually return. Giving the glovebox a good whack or driving over a pothole sometimes got it going again, leading me to believe that there might be a wiring issue. After it stopped this last time, I finally followed all of the suggestions to the previous post: I checked the fuse (good), checked the relay (good), and replaced the resistor. No change.

I reluctantly took out the blower motor today (I’m tall with broad shoulders and tend to get stuck under the dashboard, so I hate working on this). What I discovered was that the blower motor worked depending on how I positioned the power wiring that plugged into it. Strangely, the tighter the wiring was stretched, the more likely the motor was to blow at full speed. The two wires leading to the connector were wrapped in some electrical tape and a short piece of heat-shrink tubing, so I removed that to see if I could spot any crimping or exposed wire. I couldn’t, but now I can’t get the blower to spin at all.

Unless I’m missing something, it seems that I have faulty wiring leading to the blower motor. From looking at the tangled mess of wiring that the two wires powering the blower motor come from, I don’t see any easy solution if the wiring needs to be replaced. Any suggestions?

There’s no rule that says replacement wiring has to go in the wiring bundle that the original wire is in. Figure out where the other end of the wire is and run new wire from there to the motor, then ziptie it to things under the dash to keep it from dropping down.

As you are broad-shouldered and tall, this is going to be a thoroughly unenjoyable job for you, I’m sorry to say. Also, be careful under there - the dash will be held up with a steel framework that was not ever meant to be touched by the car’s owner, so they don’t bother to round or deburr edges. It’s really easy to cut yourself on it.

there is also no rule that says that a 5 month old blower motor can’t go bad. Be sure that the wiring is the issue, and not the connector at the blower motor.

Dumb question, the blower motor does not work regardless of hot or AC setting?

Most hvac blowers use a simple DC motor. The higher the voltage, the faster it spins. So it should spin like a banshee with 12 volts connected to it on the bench. Does it? If you aren’t equipped to do that experiment, take it to you local auto-electric shop, they’ll be able to do it for you. That’s where I’d start if I had this problem. first priority is to determine if the motor works reliably or not. If it does, next up is the wiring.

As George said, blowers are simple DC motors. The speed in changed by the controls by adding resisters to the motor, “dropping” voltage at low speeds and connecting the full 12VDC on high speed. DC motors operate faster as more voltage is applied.

I haven’t gone into a blower motor circuit in many years, but I have to assume that they still use a stepped-resister network to control the motor speeds. These tend to go bad over the years, usually operating intermittently on only one or two speeds but occasionally operating intermittently on all speeds.
I’ve posted a link that should help you get to the blower resister block as well as provide information on one source.

I think removing the dash is probably beyond my very limited expertise. And while I know next-to-nothing about testing electrical components, would connecting a multimeter to the connector on the wiring (not the connector on the blower motor itself) possibly confirm a wiring problem?

Possibly yes, but you still need a wiring diagram to find out which wires to test for continuity.

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Turn key to RUN but not start.
Set HVAC blower speed to maximum. This will supply full power through a relay to the blower motor.
Disconnect blower motor connector
Set your DVM to DC volts and probe across pins in connector.
You should see something close to 12 volts DC.
If not, wiggle wires to see if it comes and goes as an intermittent.

If no voltage or intermittent, you can find out which connections are bad using resistance measurement.
Turn key to OFF
Set DVM to resistance, low scale if manual setting
Touch or connect one probe to the connector pin.
Use other probe to puncture wire insulation a few inches up from the connector on the wire connected to the same pin and check for continuity. A sharp pin pointed probe is obviously preferred for this but you could use a simple pin to make the connection and connect your probe to that.
Repeat for other wire.

Be aware it could be the motor connector as well if your harness tests good.

Thanks very much! I’ll pick up a multimeter and follow your instructions.

I suggest to look at your blower resistor. It might be on its way out and work intermittently. The reason it worked fine for a few month may have been due to less current the new blower draws. As this thing gets older and “run in” the current draw will increase. It might only be a negligible increase but enough for the resister to be unable to handle it.

I haven’t done that job on my own Corolla, but don’t think you have to remove the entire dashboard to access the blower motor. You can usually gain access to a lot of that stuff by removing the glove compartment box. That’s usually just a couple of bolts. That’s how to replace the blower motor resistor array on my Corolla.

Thanks, but I already replaced the resistor. No change.

Replacing the wiring would require removing the dash. I’ve already replaced the blower motor (a while ago) and resistor (recently).

I think what I’d do if I had that problem is temporarily connect a pair of test wires to the blower motor power input, and route those wires into the passenger compartment. Then I’d connect a volt meter up to them, place it where I could see it while driving, and monitor the voltage as I was driving around, going about my daily business. You may be able to see a corresponding drop in voltage when the problem occurs, which would mean the blower motor is probably not the problem. It won’t blow if it doesn’t have proper voltage. Then you could begin to work backward from the blower motor toward the resistor and the battery (the main source of electrical power) to find out where the actual problem is. It’s called “tracing the circuit”. This job is much easier if you have the car’s wiring schematic. That will tell you the location, coloring, and sizes of wires you are tracing. Without the schematic, it can be done, but it is sort of like trying to find your way about in a city you’ve never been to before, and without a local map.

Thanks! I just need to pick up a voltmeter. You also recommended testing the blower motor on a bench. Could I do that just by removing the blower motor and connecting it directly to the car’s battery? I don’t currently have the cables to do that, but my guess is that it shouldn’t be that hard to locate some. However, is there a chance of damaging either the blower motor or the car’s battery by bypassing everything that’s normally between them?

There is no need to remove the blower motor again. Just get yourself a couple of alligator clips and 20 feet of 14 gauge stranded wire from Home Depot or Lowes. The motor is rated at 12V, so you can run the wires directly from the motor to the battery.

I would suggest to temporarily remove the current wires from the motor to avoid feedback into a potentially bad wiring harness when you test the motor.

Yes, there is a chance of damaging something. I can’t say for certain b/c I have no experience w/that particular blower motor or how it is connected up. All the blower motors I’ve worked on are just simple DC motors and will rotate rapidly if you apply 12 vdc from a car battery or other dc power supply. There’s a dozen or more ways to construct an electric motor, but I’d guess your Corolla’s is just a simple DC motor, as is the case w/my own Corolla.

As mentioned by Kurt above, if you don’t remove the blower motor from the car and do a bench test, best to temporarily remove any other connections to the motor when powering it up with battery power. A couple ideas in the way of safety precautions, first wear eye protection. Second, powering anything for testing purposes using a car battery, be sure to insert a fused jumper wire in the circuit. That way if you get a short, the fuse will blow, rather than a bunch of sparks, heat, and potentially fire happening. Check what fuse your car uses for that circuit, and use that amperage.

The ventilation system in your car is usually run off of one fan and a series of vents, ducts and diverters. If the power to this one fan is lost, you will lose all air flow. It is possible that your cooling coils are freezing up which will reduce the air flow through your vents. The most common cause of frozen cooling coils in your car is a dirty cabin air filter. They are usually very easy to change yourself.

I picked up a multimeter and finally got around to testing today. The meter consistently reads around 12.4 V when plugged into the connector on the wiring. I maneuvered the wiring around as much as I could given that it’s very short, but as long as the leads from the multimeter were touching the connector’s contacts, I got the same voltage. Maybe the problem isn’t the wiring after all?

Since the results seem to point back to the (still relatively new) blower motor, I’ll either try to test it or just order a replacement assuming that it’s the culprit. It just seems weird that a new blower would start failing within a year. Any chance that something goofy in the electrical system damaged it? It’s annoying to think that I might have the same issue with a replacement.