521 blower motor resister

[Aswisscheese]

Has anyone ever found a replacement blower motor resister. Like something that fits and works from another vehicle? or is there a way to repair it or like say hardwire it to be on the high setting instead of low??????????????????

[datzenmike]

The Nissan set up is power to the fuse box through the ignition switch. From the fuse box to the fan motor. The on / off switch just connects the other side of the electric fan to ground or through the dropping resistor to ground. On a two speed blower motor the resistance reduces the speed. High speed is simply no resistance and the motor operates on 12 volts. If you don't have any high speed then the fuse is blown, wire broken or the motor no good.

[wayno]

You could likely just wire the motor to 12V and use a toggle switch to turn it on and off.

Are you sure that it is not running but you cannot hear it, the 521 fan motor is not that fast, full is one click of the heater switch out, 2 clicks out is medium, and 3 clicks out is low, I cannot even hear mine running on med or low when the engine is running, but I am old and appear to be half deaf as my family was listening to a movie Thanksgiving and I could not hear what was being said as the volume was so low, but it appeared they could hear it fine.

Edited November 24, 2018 by wayno

[datzenmike]

Unless damaged or modified by a previous owner it's already wired for full or high speed. All you mentioned was the blower resistor. If there is no fan at all.... check the fuse.

[Aswisscheese]

I got this truck a month ago and been going thru it and rebuilding the heater box. A friend who has a few datsuns looked at it and said the resister was blown. I have tested it. I have been spending the last week or so getting the heater core checked out and the box fixed up. I had a shop offer to powder coat it for me. So im getting there with the heat. I am also fighting a wiring mess from the previous owners.

[datzenmike]

So.... does the fan work... or not?

[DanielC]

Here is a 521 wiring diagram.

 

The diagram shows three wires going to the heater box.  There is one electrical connector connecting the cab wiring harness to the heater box, with three wires.  The heater motor is grounded by a wire going to a screw on the heater box, and the heater box is grounded to the cab sheet metal.  The blower motor resistor in inside the heater box, and the resistor has a center tap.  When you pull the heater fan switch one one click, power from the heater fan switch is applied directly to the heater motor, it runs on high.  Pulling the fan switch  out to the second click, applies power to the center tap on the resistor, and pulling the switch out to the third click applies power to the entire length of the resistor.

If the resistor is bad, the heater fan should still run on high, because the resistor is not in the circuit.

The key must be on for the heater to come on.  The heater fuse gets power through the ignition switch.

I believe the heater fuse is the second fuse in from the outside of the truck in the fuse box.

The forward side of the fuse box should have power on all six fuses with the key on.  Check this with a test light.

With the key on, and the heater switch pulled to the first click, check for power on all the fuses on the back side of the fuse box.

GLASS TUBE FUSES CAN LOOK GOOD WHEN THEY ARE BAD.  If you have an electrical problem, you must check to see if power is getting through the fuse.

There is a bunch of electrical connectors under the dash, to the right of the glove box.  These connectors connect the dash wiring harness to the engine room harness.   It is possible there is a bad connection in the connector for the heater electrical power.  There is a connector for the heater fan switch, and the connector for the heater box from the cab wiring harness.

Using a test light, just follow the wiring from the fuse box to the heater box, checking for power.

The heater fan motor has two wires coming out of it, a blue wire, and a black wire.  Between the connector for the heater box, and the fan motor itself, There is a a single connector in the blue wire.   You can apply 12 volts to the blue wire going into the heater fan motor, and the fan should should run, pretty fast.

 

That brings us back to the question above, does the heater fan work?

 

 

Edited November 25, 2018 by DanielC