# electrical schematic for MTD 31AH5C3F401 yardman blower?



## spanz (Feb 19, 2015)

have a yardman 26" 8.5 hp blower with electric motor chute control. the chute stopped moving, and I can power it with an external 12V battery, but NOT thru the toggle switch on the control handle area.

I am trying to trace out the wiring, but it is very confusing, especially with the snow blowing around me! does anyone have a schematic? it looks like there is an open circuit somewhere in my wiring harness. As I toggle the chute control, the 12V dc power drops to 3.1 V dc at the toggle switch terminals. 

It looks like there might be a series diode in the wiring harness as it starts from the 4 pin connector down near the engine. also, there is a tiny black box attached to the wiring harness....what is that thing? a relay? 

MTD was of not help.


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## Grunt (Nov 11, 2013)

Hello and welcome to the forum spanz. Here is a link to the medium frame MTD snow blower manual. The last page of the manual has an electrical schematic that MIGHT help with your problem. It does show a relay and four diodes you will have to check. I hope this helps.

http://service.mtdproducts.com/Training_Education/769-09302_medium_frame_snowthrowers.pdf


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## spanz (Feb 19, 2015)

thanks that was helpful, although not exactly what I have. Did not consider it might be an ac ALTERNATOR! I am pulling the whole harness out to work on it on a benchtop. that should get it solved.


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## Kiss4aFrog (Nov 3, 2013)

Maybe not, sorry.


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## spanz (Feb 19, 2015)

ok, here is what I did.

buzzed out the whole system. seems to work with the chute motor not installed, but hooked up.
installed the chute motor, chute does not budge
removed chute motor, replaced with Napa Parts 49-7122 window lift motor (had to tap two of the holes for a 5/16-18 thread).
new chute motor worked when not attached to frame.
new chute motor would not turn when installed in the frame and chute gear engaged.

I deduced that there was a high resistance SOMEWHERE in the harness.
finally gave up on the harness, with 15F and blowing snow all around me.
Cut harness just above the 4 pin molex connector.
there WAS some sort of device mounted right at the connector....either a zener diode (to drop the voltage) or a regular diode???
Hard wired up my own replacement harness to only power the motor and lamp without the diode in the way.
Motor turned...even when hooked to the frame. motor seemed much faster (maybe the diode WAS a zener to drop some excess voltage).
BUT, since the DC motor turned without a diode in the system, it must be a DC alternator output.
After a few tries the lamp burned out...must be higher voltage now. but since the motor is tougher, and easily replaced....I will keep IT on the higher voltage. It no longer sticks in the full clockwise position, like it used to.

NOTE: I luckily had a DPDT ON-OFF-ON toggle switch available, so I used a new switch in case the switch was hinky.

it appears there IS a relay in the harness, but seems to only power the heated hand grips. one of the reasons to NOT rewire with the heated handgrips.

Will replace the lamp and add a dropping resistor, value TBD, later on today.

ALL I lost was the heated handles, which I really did not like anyway.

If I was not in a hurry, AND if I did not want to pay an exorbitant fee, I see you CAN buy a replacement wire harness from MTD. I think it was $91. THAT would fix the diode if it was soft. 

So, in conclusion, it was either the diode, the joystick switch, or a high resistance somewhere in the harness.


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## enigma-2 (Feb 11, 2014)

May be a blown fuse. The fuse is under handle panel near switch connector. 
Replace with 5A fuse.


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## spanz (Feb 19, 2015)

enigma-2 said:


> May be a blown fuse. The fuse is under handle panel near switch connector.
> Replace with 5A fuse.


 
the fuse was good.


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