Some HVAC blower motor shenanigans

Spook50

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With a lull in orders for my driver's door window relay box refurbs and the continued search for a non Chinese located PCB prototype house for my gauge regulator project, I've been using my free time to make progress on some house projects (the work room is the big'n) and investigate some other ideas I've had. One of the big ones that tons of us have had problems with is the shameful inadequacy of aftermarket HVAC blower motors. These aren't nearly as strong as the OEM motors, shriek loudly when in operation (at least to my experience), and are simply not worth the money you spend on them. Granted an OEM replacement is pricey, but my hope is that I can "standardize" a method of restoring these OEM blowers and breathing new life into them for continued use. First order of business is finding out why they go kaput. The most common cause is simply the brushes wearing out. This would typically be an easy fix, but I've come to realize it's damn near impossible to find correctly sized brushes for these, plus the factory brushes are soldered onto the leads from the connector, making them difficult to replace unless you have some experience and knowhow with electronics soldering. Secondary to that is wear on the commutator itself. In most cases this is repairable simply by cleaning up and smoothing out the segments again. I know a few tricks for accomplishing that but also have an old metal lathe I'll be restoring that will really help with that.

The differences between the OEM and aftermarket motors are significant. To start with the housing, which holds the stator magnets, the magnets in the OEM housing are considerably larger. While only slightly thinner than the aftermarket magnets, they measure 39mm long versus the aftermarket 32mm long. Despite being slightly thinner I suspect the much larger face leads to a much stronger magnetic field. Though I can't say for sure I suspect this results in a higher RPM under the same current draw.

On to the rotor assembly, the OEM unit is far more rugged, as can easily be seen just at a glance:
Rotors.jpg


The armature section is not only longer than that of the aftermarket by 11mm (20 for the aftermarket vs. 31 for the OEM), but OEM has 12 segments instead of just 10. So there's far more wire wound around the OEM rotor than the aftermarket. Like with the larger magnets, I believe this translates out to higher RPM (or if not that, more torque throughout the RPM range) while drawing no more current than the aftermarket.

The brushes for the aftermarket motor I lost since taking this one apart, so I can't say what the size comparison is there unless I find them later on.


So I'll be starting with just the basics on this project and hopefully collecting a few more "safe to destroy" blower motors to conduct further experiments with as time allows.

First of all: New brushes. The OEM brushes are 6mm wide x 7mm tall, and (as best I can guesstimate when new) ~12.7mm (0.5") long. The search is still ongoing for a reliable bulk source, but in the meantime I have a pair of brushes I ordered a while back from Roger Brown that pretty closely match the OEM size. They install the same way I intend to have bulk brushes I order install, so these will work for now. They're slightly smaller than OEM size, which means less contact area against the commutator once they're bedded in (3.3mm² less contact area). Exactly how much of a difference this will make in motor performance, I can't say. Unfortunately I struggled with understanding the more advanced information on DC motors and magnetic inductance that was taught when I was taking my course. But to put it in perspective we're talking about an 8% reduction in contact area per brush, so I can't help but feel this does make a difference.

That's all for now. I'll update likely this weekend when I can do a little more research and hopefully some work on a motor.
 
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They should resurrect ok with new brushes . Soaking the brass bushes in the proper oil for a day or 2 might be helpful.
Not sure if the ceramic magnets lose their oomph over time?

The oem's are certainly the better unit looking at that pic.
 

Spook50

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They should resurrect ok with new brushes . Soaking the brass bushes in the proper oil for a day or 2 might be helpful.
Not sure if the ceramic magnets lose their oomph over time?

The oem's are certainly the better unit looking at that pic.
Typically this is the case. Unfortunately unlike the starters, Nippon Denso didn't design these with serviceability in mind. The leads for the brushes are soldered into place so your typical "Joe Shadetree Mechanic" can't easily replace them. I'm trying to find a feasible solution for that though. I have the principle figured out, but need to find the perfect parts to use that also have bulk availability.

To coincide with that is also wear to the commutator, which is rarely extreme and can be corrected with resurfacing and cleaning. What I need to find out though is just how thick the copper segments are so I can find out how much leeway I have with resurfacing it. I need a rotor assembly I can freely destroy though to find that out by just turning it down until I get down to the phenolic support and measuring with a micrometer.

As far as the magnets, I think any loss unless subjected to extreme heat for long periods of time is negligible. They typically don't "wear out" like other parts do.

Definitely seeing a renewed sense of motivation to start on that lathe and get it running.
 

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Another way to look at it is aftermarket parts are designed and priced to be disposable and easily replaceable - because they don't cost much. It's the Chinese way. So while these "cheapo" knock off blower motors may not have the same quality as the original, they work fine (I had one) and I can attest that they blow air faster than an old worn out OEM motor. No complaints there.
As to how long they last? It's been four years now and it's still cranking. When it burns out some day I'll just get another one.
 

LazarusTaxa

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Ahh man, why'd you post this now?? I JUST threw in the towel and ordered a four seasons replacement and at the same time threw away my old blower parts. I'd wanted to do this same refurbishment...

To coincide with that is also wear to the commutator, which is rarely extreme and can be corrected with resurfacing and cleaning. What I need to find out though is just how thick the copper segments are so I can find out how much leeway I have with resurfacing it. I need a rotor assembly I can freely destroy though to find that out by just turning it down until I get down to the phenolic support and measuring with a micrometer.

The commutator on mine though was what made me feel like I needed to get a replacement. My brushes were mostly gone but measuring the copper tabs on my commutator, it seemed like they were roughly halfway worn through (I don't remember the exact measurements). I know it can be resurfaced but I suppose I figured an aftermarket replacement might last longer.

I wondered if there is a replacement blower for another Toyota which might use the same armature?
 

red66toy

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Ahh man, why'd you post this now?? I JUST threw in the towel and ordered a four seasons replacement and at the same time threw away my old blower parts. I'd wanted to do this same refurbishment...



The commutator on mine though was what made me feel like I needed to get a replacement. My brushes were mostly gone but measuring the copper tabs on my commutator, it seemed like they were roughly halfway worn through (I don't remember the exact measurements). I know it can be resurfaced but I suppose I figured an aftermarket replacement might last longer.

I wondered if there is a replacement blower for another Toyota which might use the same armature?
I think raiding other Toyota models is always a great idea and can extend the lives of our rigs when some parts go NLA. I keep wondering if a modern Toyota motor would be made to work. It would be fantastic to find a high quality Denso replacement.
 

Spook50

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I think raiding other Toyota models is always a great idea and can extend the lives of our rigs when some parts go NLA. I keep wondering if a modern Toyota motor would be made to work. It would be fantastic to find a high quality Denso replacement.
I think a perfect solution would be a brushless motor with a PWM controlled by the factory 5 position switch. Not impossible, but a big expenditure. I don't see many willing to cough up ~$500 for an HVAC blower upgrade on these rigs.
 

LazarusTaxa

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I think raiding other Toyota models is always a great idea and can extend the lives of our rigs when some parts go NLA. I keep wondering if a modern Toyota motor would be made to work. It would be fantastic to find a high quality Denso replacement.

Yeah, if you look at motors for any 80's toyota, they all look relatively the same. I'd bet Denso is using the same components in the motor with slightly different housings.
 

Spook50

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Yeah, if you look at motors for any 80's toyota, they all look relatively the same. I'd bet Denso is using the same components in the motor with slightly different housings.
My thought as well. Though I haven't looked yet, I'm willing to bet anything through the mid 90s would have good odds of matching parts.

Really the critical part is the rotor assembly. If identical can be sourced, that'd be the real ticket. Housings don't wear out and brushes can be replaced with a little knowhow.
 
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Spook50

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A bit more messing around yesterday and today. Both of my OEM rotor assemblies are slightly bent, and with my old lathe dismantled I have no stable way to chuck up the assembly along with a dial gauge so I can get them straight again. I want them as straight as possible for the sake of being better balanced and hopefully quieter than they would otherwise be. Trying to find someone nearby who can help me out. Worst case maybe I can use the lathe at my work, but I don't really have easy shop access since I work electrical testing, not maintenance/design.

Meantime, I cleaned the cap and housing real good and until I can figure out an alternative to the factory installed bronze bushings, I soaked them in 3-in-1 electric motor oil and baked them at about 190° for a few hours. My hope is the heat will open up the pores in the bronze while thinning the oil enough to creep in and saturate it for a little more long term lubrication under use. I didn't want to go any warmer because of the risk of actually burning the oil, and damaging the magnets in the housing. 190° had already discolored the oil so I think that was my limit.

Motor bushings.jpg


One day this week I'll clear off a spot to solder the leads into place on the brush holder and pop the Roger Brown brushes in. Once I can get to a lathe I'll be able to straighten out the rotors and get the commutators set up good, then reassemble and break in the brushes.
 

Spook50

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??How. maybe they were like that from new
I doubt it. Maybe not LASER straight from new, but these are several thousandths off so I suspect the assemblies have both been dropped at some point in their lifetime. Possibly even by me since they've been in my possession so long and moved around so many times.
 

Spook50

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On second thoughts , I have tried to straighten out an out of wack squirell cage fan a few times, so I can see how that could happen.
I suspect a bent shaft (ha) contributes a great deal to performance loss, excessive brush wear and overall noise in general. Though I think just how far it's bent plays a big factor in how severe those conditions end up being.
 

Spook50

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So last week I was able to straighten out a rotor assembly to within a couple thousandths of an inch, using the armature as a reference point in my temporarily reassembled lathe (got to use my nice new Mitutoyo dial gauge. Woooooo I love precision equipment). I still wasn't able to do a legitimate turning and reconditioning of the commutator, but did improve it a great deal. I think once I can do it "right" it'll be even better, but this was a good starting point (no pictures here; forgot to take one). I also found brushes that are just a hair larger than the stock brushes and with reaming out the brush holders about 0.25mm to accommodate them will work beautifully. They have built in shunts running through their springs to contacts and are considerably larger dimensionally than the Roger Brown brushes. I'm sure the Roger Brown brushes would work just fine too, but wanted as large as I could go without extensive modification to the holders. With the better brushes, I had to modify the holder so I took some of my nice silicon insulated 14ga wire and soldered small jumpers from the connector to the brush holders. I like the way this works out because as long as new commutators can sourced or machined this allows indefinite life with regular maintenance.

Brush Holder.jpg


With the rotor assembly ready, everything cleaned, straightened, re-oiled, and new brushes in place I reassembled the OEM motor. I expected some degree of break-in time being necessary given the need for the new brushes to bed in against the commutator, which turned out to be the case.

Initial finding was definitely a slower moving motor that over the course of several hours increased a great deal, to as least as much airflow (possibly more but I haven't done my rudimentary measurement yet with my anemometer) as a new VDO/Four Seasons motor, and significantly quieter! I had to listen closely to hear the motor running, which is a massive improvement over the aftermarket garbage available for our trucks.

A caveat to this motor I just refurbished, is that since the commutator wasn't resurfaced in what I feel is an ideal way, the brushes WILL wear through sooner than an ideal refinish would result in. I'll be running this fan hard as much as I can to get an idea what my next steps will be in experimenting with a proper refurb process.

For now, it'll be run as normal and if there is any change whether good or bad worth noting, I'll update the thread. I don't expect we're there yet with a viable OEM motor refurbishing method, but a few very big steps along the way. Caveat: I do expect that given the time and work necessary to properly refurbish an OEM blower motor, price could be fairly high. My goal is to have it be no higher than $250 per unit (which would involve sourcing available parts for spares, investing in a test bed, and the time it takes per unit to do the work RIGHT).
 

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