Heater blower motor Mod with MRAP blower

I am using the 42 amp version, there is a 28 amp but all the ones I had were going to need lots of works. This one was clean, the smoke had not been let out of the wires yet so it got used.

Check the donor MRAP fan motor to make sure it works. Pin B is battery and Pin E is ground, they are both large pins. I used 10-12 gauge butt connectors with a short run of wire. I just tested on a 12v battery charger with a 50 amp boost. Also make sure there is very little bearing play or it will ruin the squirrel cage and air chute because it wobbles too much.



Strip off MRAP air chute and fan. Easier said than done. Take off screen and foam, save the 3 screws. Remove the 6 allen skrews around the outside. No need to remove the 4 small ones on the inside, it all comes off together. Use the 3 screws from earlier to use as pusher skrews, these are counter sunk mated surfaces, so do like 1 turn on each screw or it will bind up.



That is about the worst part of dissassembly. Take off nut, and slide fan off. Next flip it over and take the 6 allen screws off the back. The worst screw is directly under the power connection box, I try to do it first. When its all done it should look like this.



The original squirrel cage and air chute will be used from the 5T. So take the old motor off, make sure and save the set screw from the squirrel cage, but dont leave it in the cage. The cage must be drilled out to fit the new shaft. Drill bit size for the squirrel cage hole is 25/64th. I also had to 'polish' the shaft on the new motor with some emery cloth just a little bit for the cage to slide on and off easily.

Insert photo

Next the holes on the motor have to be enlarged, the first one I built I drilled all the holes 5/16th, but the last bolt to put in was a bear, so the 2nd one I drilled 5ea at 5/16, and 1ea at 11/32nd, make sure to mark the 11/32nd and let it be the last bolt you put it. Use 5/16 x 1" bolts. I used non locking nuts first, then teflon locking nuts on last. Install 3 or 4 bolts in the motor and start non locking nuts. Then set the cage and air chute on. Leave the cage loose you will need to wiggle it around to get the other bolts in. Drop in the remaining bolts and nuts leaving the 11/32nd hole for last which should be next to the exhaust air opening.

This is what it looks like without the cage mounted on the motor.






This is a shot from the exhaust air chute with the install almost finished. Tighten the non locking nuts, some will need backed up, others will not need a backup, the lands of the head will hit. Tighten pretty tight, german spec's.... goot n tight. If you tightened them tight enough, you can put the lock nuts on with no back up wrench needed.



Almost done, just need to adjust the fan to the chute, the fan is fairly bendable to get it to run straight. I adjusted mine with a gap of about 1/8th" Tighten the set screw in the keyway.
I bench ran mine about 10 minutes, then tightened the set screw again and got another 1/4 turn out of it.



Lastly, there will need to be a trimming of the fins on the motor when it gets mounted to the truck. The motor is aluminum cased so a dremmel worked wonders at trimming the case.



For power I used a butt connector and the power wire from the old motor, and a ground wire to a bolt on the air chute. Vola new heater motor.

So im pretty oblivious here but how much harder does this blow than the oe unit? I know on high mine is about as powerful as a gerbil fart.

big block 88 said:

So im pretty oblivious here but how much harder does this blow than the oe unit? I know on high mine is about as powerful as a gerbil fart.

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I know the 1st one i built had some engineering 'issues' so I cant run it on high, but low was more than enough to keep the window defrosted at 0*F when we played Sat. morning and it did blow all the bugs and dust out of the defroster which had an old motor running a few hours earlier.

Wow, this a is a total win! Nice work. If the motor is the same RPM, then the gain may be near zero. But, I would have hooked it up as-is and checked out the airflow with the impeller and hosuing it came with. I can't believe it pulls 42 amps @ 24v. That is a silly amout of power for just a fan motor. I thought it had a grid heater as part of it, but appears not. I'd like to get one of these, transplant it as-is onto my 925 in place of the anemic stock one, and add a Dodge Ram Cummins 5.9L grid heater to it. As soon as engine fires, turn on heat and it blows warm immediately!

I just snacked one from eBay, possibly you were the seller. Going to try it as-is, or add the grid heater. Love home brew science experiments.

I couldn't come up with an easily engineered way of using the whole fan and air chute. The 5T has a big square hole and the fan had a small round exhaust outlet. If you figure a way to use the whole fan, I would like to see.

I was was not the seller on fleabay.

Growing up up on a farm, I learned from a young age how to southern engineer, when it's hay baling time, there isn't time to wait on ordering parts.

For reference, here's the one I'll be working with when I find time to pick it up. I plan on using the fan housing as pictured. I should be able to screw it to the box after removing the old one. I can see the difficulty in making the housing easily work that you have.

74M35A2 said:

I can't believe it pulls 42 amps @ 24v. That is a silly amout of power for just a fan motor.

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I dont think with this build it could pull that many amps, there isnt anyway to load that small squirrel cage that much. I could see how it would pull that much with the original fan and housing, small intake hole size and even smaller exhaust hole size.