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Blower Motor

John Stamey

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Power TO the fan motor is through a relay that is turned on by the ignition switch. To activate the fan the other side of the motor is grounded by the fan switch. Speeds are provided by multiple resistances with the highest speed having no resister at all and having full voltage.


If your horn works then the fusible link is alright.


Power is through a 20 amp fuse that is 10 over from the left side of the fuse box. If blown then there is no power to the fan. Never trust looks, test with a test light or meter.


The 1" square plastic heater relay and the headlight relays are mounted on the top of the fuse box with the heater relay the left one. If you have electric windows there are three relays and the heater relay will be the middle one. The relay should click when the ignition is turned on.



Does the fan work in the high position? but not on the lower speeds? 






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4 hours ago, Stoffregen Motorsports said:

Does the 720 have a relay, and not a resistor? A bad resistor will run the fan on high, but not at lower speeds.


Has both. Fusible link (Black) to fuse box. #10 fuse (20 amp) to relay. Ignition ON trips the relay sending power to the heater fan. Fan is grounded by the heater fan switch which selects resistances to ground to slow the speed or directly to ground for highest speed.. 

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On mine before I got my new custom made heating and Air.The yellow 20 amp fuse would pop out and my blower motor  would stop working.The part that would hold the fuse was burnt and the fuse wasn't getting a good connection.I ended up bending the fuse prongs to make it seat in there tight and it worked.I no longer have any Nissan heating and air parts in my truck,mine has been rewired.But I do have the original blower motor that works and a brand new white resister that I got from Nissan long ago that is still new in box for sale,the resistor does not fit my 85....271They gave me the wrong one,the right one is black.I bought a new resistor,new blower back then and it was the loose 20 amp fuse.So check the fuse box where the 20 amp fuse goes,it may be melted.27150--03WOO.The White one is a 3 -Speed,black one is a 4 -speed one.The white one is no longer in stock at Nissan but the black one is.27150-62W20.


These resistors have an onboard fuse

The original ones were two strips of copper with a solder blob holding them together

If your resistor fuse is blown, there are two things that you must check and correct so that you do not blow the fuse on your new resistor

1) Bad or dying blower motor- make sure your blower motor spins freely and runs at full speed when tested with 12 volts

2) Because the resistor generates heat during operation, it is installed such that air blows across it
Low air flow from either a bad blower motor, or an obstruction such as leaves, paper, animal nest, a rag, etc will cause the resistor to overheat and melt the fuse

So if the fuse on the resistor blows, it is not because the resistor is defective, it is because something blew the fuse

Another problem with the earlier fuse design, is that it used a ceramic screw to hold everything together
These ceramic screws were prone to break, which causes all of the fuse parts to fall off and get lost, resulting in an open circuit
You will notice that the new resistor uses a metal screw so that this can not happen






Edited by Thomas Perkins
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