Front Blower Motor Issues, Not the Usual Suspects

Zaphod

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2007 Mazda CX-9 AWD
So, I should probably start by apologizing for bringing up this topic, since it's been beaten to death so much on here, but I've been through everything I can find and could really use some advice on how to proceed

It's a 2007 CX-9 AWD

The problem started with both the rear and front blowers going out. Started with replacing the fuses, then the relays, which only got the rear working again, not the front. This is when I learned about the issue with the AC condenser, which definitely turned out to be part of the problem. Was able to get it all drained out using the shop vac method, and just assumed the blower motor was toast (shorted out), so I went ahead and ordered a replacement. Very easy swap, but the motor still doesn't kick on

I've gathered a fair amount of information so far with my fluke, but haven't been able to pinpoint if I should replace the blower motor resistor. Does anyone know a proper test that would tell me for sure that the resistor is bad? I've tested the motor using a separate 12v source, and it seems to be fine. And when I have the car running, I can slightly connect and disconnect the cable going to the motor, and it kicks on very briefly. Sticking the meter on the motor cable shows that I have battery (~14v) with the cable disconnected, and it drops down to 0v when connected to the motor (good chance the resistor is the problem maybe??)

I also thought it would be interesting to take some measurements on the resistor assembly itself. There are two visible resistors that check out to ~2.1k and 1k, but the 2.1k resistance reading also drops to 0 when the motor is connected (bad resistor possibly??). Voltage readings on the resistor assembly are the same. ~14v when the cable is not connected to the motor, but 0v with the motor connected

Is this enough information to say for sure that the blower motor resistor needs replaced? Or is there something I'm missing? Still trying to find a schematic of the HVAC system in the manual, but haven't found it yet. Haven't been able to locate the part at a junkyard, and it looks like the cheapest I can find it is $105 on partsgeek. It was easy to spend 40 on the replacement blower motor, feeling that it needed replaced regardless. But I'd really hate to be guessing wrong on the resistor since it's a little more expensive

Any help is greatly appreciated! And hopefully this hasn't been answered yet, cause if it was, I couldn't find it (and I read through a ton of threads on this issue, believe me)
 
So, I went ahead and jumpered over the resistor once I found the proper schematic. Sure enough, the motor kicked on full blast. Of course, there was no speed control, and it couldn't be turned off, but this made me quite confident that the resistor was the part that needed replaced

Ended up getting it from Napa delivered next day at $128 (not too bad). I installed, and everything worked again! I was very happy, for a very short period of time. About an hour later (after my wife was driving the car for a little bit), the front air is no longer working again with the same symptoms as before :(. The only thing I know is when I installed the new resistor, I kind of had it siting on the floor of the passenger side with the intention of installing back in position later that night, but I highly doubt this caused it to go bad in such a short period of time. There's gotta be something else, I'm going nuts here! There's nothing else in the circuit that I know to look for or check. Winter's coming soon, and this thing's gonna be a b**** without air to defrost the windshield. I'm seriously debating installing a jumper with a toggle switch, I don't know what else to do
 
If the new resistor was run for any length of time (>2 min) without it being in its factory location it most likely damaged it. The factory location pulls air over the resistor to cool it. There is a thermal cut out fuse that would blow, inside the resistor if it reaches an unsafe temperature.
 
Thanks for the reply! Luckily, I was able to get the part replaced, it'll be here tomorrow.

I was doubtful that such a short period could've damaged it, but I guess I was wrong. It ran for like 20 minutes like that.

When I get the new one, I'll be sure to install it into the factory location before using it
 
Please update us if this fixes it permanently

So far so good! Installed it slowly and as properly as I could, with the negative terminal disconnected (another mistake I think I made last time). Drove around for a little while with a meter connected to the motor input, and watched it changing as I changed the fan speed to assure it was still working (i'm kind of nerdy with electrical stuff that way, so it was kind of fun to see it actually working the way it's supposed to. Was also a good opportunity to talk to my teenage daughter about how such electrical circuits work).

I say, give it one more day. As long as everything is still work in the morning and throughout the day, I'll be confident that it's [finally!] solved. Been working on this for at least 6 months now! Being without air is lot more of a nuisance than would be imagine, especially in cold weather
 
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