2009 Mazda 5 blower motor diagnosis

My 2009 Mazda 5 "sport" stopped blowing air through the front blower the other day.

I did a bunch of research, want to share what I learned here because I didn't find the answers so easily in other places.

My car has automatic climate control (9 or 10 blower speeds with an LCD display), and has a 2-speed rear vent between the front seats which seems to blow cold air only. Parts diagrams indicated different parts for manual (never seen it) vs automatic climate control, and draws a distinction between those which have "rear ventilator" and those which do not. I guess I've got rear ventilator, but am not familiar with the more upscale models to know if there are additional rear vents missing from my car.

Many cars use a resistor pack to control fan speed. These are typically for cars which have 4 fan speeds. Speed 1, 2 and 3 run the blower power through a resistor block that's installed in the air ducting for cooling purposes.

That's NOT how my 5 works. My 5 has a MOSFET fan driver, not resistors, in the ducting in passenger footwell. 3 wires attach:
  • blue/yellow signal wire
  • blue/orange fan wire (heavy gauge)
  • balck ground wire (heavy gauge)

The fan is powered from the other end via relays and whatnot. The MOSFET box in the passenger footwell controls fan speed by modulating ground.

Accordingly, the blue/orange wire always shows voltage, because it's coming from the fan.

The path is:
  1. Battery
  2. Underhood Fuse(s)
  3. Underhood Relay(s)
  4. Front Blower Motor
  5. MOSFET box (in via Blue/Orange wire)
  6. Ground (out via Black wire)

If the fan is "on", but not running because the MOSFET is bad, the blue/orange wire should be at relatively high voltage (10+V). That voltage is coming through the fan motor coils and not finding its way to ground.

A working MOSFET box pulls that blue/orange wire to ground, causing the fan to run.

The MOSFET box takes a PWM input signal on the skinny blue/yellow wire.

The PWM signal switches on and off really fast. Whenever it is ON, the Blue/Orange wire is pulled to ground.

So, the Blue/Yellow wire (PWM signal) voltage (average) should be inverse of the Blue/Orange.

At low fan speed, the PWM signal should read around 2-3V and the fan should be around 8-10V. As the PWM voltage approaches 12 (really it's just on "more of the time"), the fan (blue/orange) voltage should approach zero (grounded "more of the time).

Putting a test lamp on the PWM signal might not be safe. I don't know how much current the climate control is intended to source. It's probably safer to just use a voltmeter on the blue/yellow wire.

Inside the MOSFET box there's a thermal fuse intended to pop at 133 degrees C. It's secured to the heatsink with a clip, screw and thermal grease. It's the first place that the PWM signal goes once it enters the MOSFET box (before it gets to the actual MOSFET drivers in the box).

The fuse was bad in my unit: Mazda # CE4961B15, stamped HB180BP4M is a $100-ish part. For a quick check, pop the plastic lid off the MOSFET box and follow the circuit trace for the PWM input signal. It disappears under the board into a through-hole component (the fuse) and re-appears on the opposite side of the board at an identical spot. There should be continuity between these points.

Fixing the fuse requires unsoldering one of the MOSFETs and the fuse from the board inside the box, because they're screwed to the heatsink and then the board is soldered down on top of them. The other MOSFET screw is easy to reach, so it can stay attached to the board.

A high-wattage soldering gun is probably appropriate here, because these are big components and several spots need to be desoldered at once.

The fuse should be just a few cents. The interesting thing about this fuse is that, unlike others I've seen, this one has a ceramic body. Most axial type thermal fuses have a metal body which is connected to one of the legs. Because this fuse is mechanically secured to a metal heatsink, that difference might be important.

The fuse is marked with the following:
Code:
12X   UMI
133C N3  <- There's a "degrees" symbol (133 degrees C) there, but I don't know how to type it here.
2A 250V~
3.5A 125V~
<PS>E JET

Edit: This guy shows how to get to the MOSFET: http://www.youtube.com/watch?v=jgxP6s-_JqM

He and the Mazda parts counter both refer to it as a "resistor"
 
I hadn't diagnosed the fuse problem with my MOSFET box before ordering a new "resistor" from the Mazda dealer.

I placed that order, and then ripped the old box apart, learned about the fuse, etc...

Well, the new box came in and I popped it into place without installing it into the duct, and it promptly overheated and blew the same fuse. <sigh> I definitely should have known better.

The replacement unit is a different design than the original one.

My original MOSFET, described above, was a large cast aluminum heatsink with a black plastic cap covering the electronics.

This new one has an extruded aluminum heatsink and a two-part plastic case around it, instead of a single plastic cap.

It's also much easier to service, because the screws securing the components to the heatsink are directly accessible, rather than being hidden under the soldered-into-place circuit board. This is a big improvement. The thermal cutoff in this one is rated for 127C.

Both units have insulated style thermal cutoffs (fuses). They look like this:
images

Not like this:
images


Because the fuse screws down to metal parts, and the signal coming from the (presumably expensive) HVAC control unit flows through it, using an insulated TCO is probably a good idea. The non-insulated style would direct the PWM control signal into the heatsink with unpredictable results.

I think that Panasonic EYP2BN134 or EYP2BN127 is probably the correct replacement part.
 
I've just repaired both of my motor controllers with new TCOs (Panasonic EYP2BN134 ) purchased online for just a few pennies each.

I snapped a photo with the covers off to show the difference between my original controller and the one purchased at the dealer.
cU3Q3RN.jpg


The one on the left is the original. There are 3 screws holding components (two drivers and the TCO), but only one of them is accessible. Unsoldering these parts all at once, without moving them is tricky. In the end, I just unscrewed the one screw I could reach. The clip holding the TCO is very thin, will bend to release it when pulled, so I levered the circuit board out of the way (bending leads on the remaining driver) until I could reach the 2nd driver's screw.

The one on the right is the one I purchased from the dealer. It only has two screws, both are accessible. This one is much easier to repair.

I've circled the points where the TCO connects to the circuit board on each model. To test for TCO failure, look for continuity across these two points. If there is no continuity, then the $100-ish controller has probably stopped working due to the failure of the < $1 TCO.

Don't forget to get some new silicone heatsink grease if you attempt to repair one of these guys. Also, don't short the connections, bypassing the TCO. You're dealing with a 40A system. The TCO is there for a reason. This is potential car fire stuff. Spend the couple of dollars and do it right.
 
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TCO fuse for Mazda MOSFET module for hvac fan

I've just repaired both of my motor controllers with new TCOs (Panasonic EYP2BN134 ) purchased online for just a few pennies each.

I snapped a photo with the covers off to show the difference between my original controller and the one purchased at the dealer.
cU3Q3RN.jpg


The one on the left is the original. There are 3 screws holding components (two drivers and the TCO), but only one of them is accessible. Unsoldering these parts all at once, without moving them is tricky. In the end, I just unscrewed the one screw I could reach. The clip holding the TCO is very thin, will bend to release it when pulled, so I levered the circuit board out of the way (bending leads on the remaining driver) until I could reach the 2nd driver's screw.

The one on the right is the one I purchased from the dealer. It only has two screws, both are accessible. This one is much easier to repair.

I've circled the points where the TCO connects to the circuit board on each model. To test for TCO failure, look for continuity across these two points. If there is no continuity, then the $100-ish controller has probably stopped working due to the failure of the < $1 TCO.

Don't forget to get some new silicone heatsink grease if you attempt to repair one of these guys. Also, don't short the connections, bypassing the TCO. You're dealing with a 40A system. The TCO is there for a reason. This is potential car fire stuff. Spend the couple of dollars and do it right.



What would cause the fuse to open? If it continues to open after replacing, what could be the cause? I will be ordering the fuse and replacing, but was also wondering if a bad MOSFET (or bad heat sink cement) can be causing this due to the heat they create. Thanks for such a detailed explanation for this problem. No one else has explained anything about this being just a fuse, so it will save me tons of money! Much appreciated!!
 
What would cause the fuse to open? If it continues to open after replacing, what could be the cause? I will be ordering the fuse and replacing, but was also wondering if a bad MOSFET (or bad heat sink cement) can be causing this due to the heat they create. Thanks for such a detailed explanation for this problem. No one else has explained anything about this being just a fuse, so it will save me tons of money! Much appreciated!!

The only thing that should cause the TCO to open is heat. There's some wax/plastic inside which keeps some spring-loaded metal bits in contact with each other. If the wax melts, then the metal bits lose contact. I don't think it provides any over current protection, it's thermal only. Of course, there's fragile parts in there, so bad luck could be a factor as well. https://www.amazon.com/dp/ (commissions earned) seems to eat one of these TCOs every year or so. It's not subject to vibration and (pretty much by definition) isn't subject to heat > 212F. <shrug>

A bad MOSFET could trigger the TCO failure by spinning the fan too slowly while the heater is running, leading to too much heat build-up (too little airflow over the heatsink), I guess. Shorting the points I circled should rule that out pretty quickly: If the fan runs like crazy while you're jumpering over the TCO, then the MOSFETs are doing their job, right?

The main objective here is to dump MOSFET heat into the air duct. If the fan can't turn, the TCO stops the MOSFETs from burning the car down by interrupting their driver signal.

Spitballing about the transfer compound... The only place I can imagine a lack of transfer is into the TCO from the heatsink, because the MOSFETS are nice and flat. There's just not much opportunity for the MOSFET->heatsink path to go wrong. Failure do deliver heat to the TCO seems more probable (cheap clip, round part) but doesn't sound like it would lead to a failure of the TCO because the TCO would run cooler in this scenario.
 
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