Usually by the time that the blower wheel needs to be replaced you only have about a 1 chance in 10 that you can get it off the motor shaft. Since it sits in the exhaust which has both heat and water vapor as components the motor shaft, blower wheel hub and set screw are normally badly rusted and you might have to hacksaw the motor shaft just to save the blower housing meaning you still have to replace both the blower wheel and the motor. If you can match up the motor and the wheel and the housing is still in one piece it is doable. Be careful about matching the rotation of both the wheel and the motor. The cups (concave side) of the vanes in the wheel must rotate in the direction of the housing outlet (toward it). The rotation of the motor must move the blower wheel in this direction, but be careful as the rotation of a motor can be listed as either lead (electrical lead) or shaft end and cw (clockwise) lead end is the opposite direction of cw shaft end. Rotation of a motor can also be listed as ccw (counterclockwise) either lead end or shaft end. Of course you could be the lucky 1 in 10 that can get the wheel off of the motor shaft with lots of some type of rust buster. Access to the allen wrench set screw is through a half-circle cutout in a vane opposite the set screw by lining it up with the housing outlet or by using the short side of a 90 degree allen wrench.
Please take the following with a grain of salt!
As a tech, the above paragraph took more effort to write than i would be willing to put into a MiniMax NT. Apologies but, that's just the kind of heater those were. If you had that heater for 10 years without much trouble, you got more than your moneys worth out of it. Perhaps its time to budget for a new replacement.
I dont care to "repair" big items like blowers. Murphy's law dictates that when you replace a part within an old part, you now have a new part surrounded by an old part, a polished tur# if you will...
Sure it may save you some money in the short term, but usually something else within that item will fail not to far down the road.
If you are willing to take that on, and attempt to replace the squirrel cage, more power to you. That is well within the DIY realm encouraged here. Just know going into it that it may not be fixable.
Its just not that economical from a labor rate per hour perspective to "
have" it repaired mainly because of the uncertain outcome of the repair.
That seems to have been my luck with repairing old heaters, sometimes you get the heater, sometimes the heater gets you...
