Alternative For Fan Resistor

RBBailey

Well-known member
Callsign: KF7KFZ
My fan resistor is apparently dead since the fan only works on what Land Rover has jokingly called "high" for many years.

Are there any viable alternatives that wouldn't be too difficult to make fit, and wouldn't cost as much as one of the originals? And are there any magicians who know of a way to change the thing without taking the wing off?
 

NPT90

Well-known member
on a RHD defender the box comes out without issues, it's only held on by 4 bolts IIRC. If not the resistor is housed on top of the heater box, if you can see where the wiring attaches to the box (then to the fan) I believe it's screwed in place (though it may be riveted).

I am pretty sure anything that would fit would achieve the same result as far as the fan resistor. Since the 'low speed' is essentially just an inline resistor to earth you could just eliminate it or replace the 'low speed' resistor with anything 10ohm for a factory low speed or, if it were me, I would probably find a factory 6 or 8 ohm to increase the low speed a bit.

 

RBBailey

Well-known member
Callsign: KF7KFZ
It's LHD......

I think I know what you are on about. But it has brought up a question -- maybe it isn't the resistor? Maybe the switch? I have what I think is a three speed switch from an NAS 110. The fan only comes on when in high. So either the resistor in the fan is dead in a way that does not allow the fan to turn on at all (because isn't the high setting just running without any resistor?) or the fan switch is dead at the first two settings. Or.....?

I may be able to figure it out, but how would I test?
 

Red90

Well-known member
If you have non-standard wiring, you will really need to investigate what is going on. The stock system is very simple as shown above. The switch is on the ground side of the circuit.

You mention that the fan is a "joke" on high. It should not be. The fan has more or less as much flow as most car heaters assuming we are talking of the normal heater. Maybe you should start with explaining what exact heater you have in the truck. Has it ever been overhauled?
 

RBBailey

Well-known member
Callsign: KF7KFZ
I have a standard LHD heater fan and box. But on the inside it is an NAS 110 dash. So you have to remember that instead of feeding air to the floor and defrost only, mine also comes out of 6 dash vents, after getting lost in the mines of Moria (interior dash) on the way there. It spreads out quite a bit compared to the standard four vents in a Defender. So I do think my fan is working well. It is quiet, and pops on nice and quickly.

This is the switch that is in the dash. And when I wired it up, I knew it wasn't the same as standard, but I figured that one of the low settings should also feed 12v to the fan, where the resistor is. However.... now that I'm thinking about it.... this switch might actually be providing a lower voltage already, except for when on high. But I can't find information on the switch enough to know.

https://cdn.autodoc.de/thumb?m=1&id=10090627&lng=en&ccf=21875996
 

Red90

Well-known member
This is the switch that is in the dash. And when I wired it up, I knew it wasn't the same as standard, but I figured that one of the low settings should also feed 12v to the fan, where the resistor is. 6
The switches do not provide 12V to the fan. The fan is switched on the ground side. Please carefully review and understand the diagram posted above. Then follow the wires and make sure it is wired exactly as shown.
 

RBBailey

Well-known member
Callsign: KF7KFZ
Yes, it is as shown. It's using factory wiring. Only difference is the switch itself. It is the one posted above, labeled ERA 662193.
 

Red90

Well-known member
Okay. Check for voltage at the low speed wire to the switch with the ignition on. If there is not voltage there, check at the heater plug. If there is voltage, jumper the wire to ground.
 

RBBailey

Well-known member
Callsign: KF7KFZ
Right, the fan should run when jumped to ground, on each of the two wires, one low, the other high.

Checking the switch might take a bit as it is behind the main dash facia.......
 

NPT90

Well-known member
its pretty easy to get to, its like 5 screws, the housing for the switched has a ground wire and the 2 contacts are spring loaded clips.

It could easily be the fan itself at this point as its pretty aged
 

RBBailey

Well-known member
Callsign: KF7KFZ
Yeah, it's just that I had it off for a year, and only got it installed this summer! That plastic scares me to fool with it. Don't want any cracks.
 

brdhmltn

Well-known member
The ohmite website has some good candidates for a replacement resistor. The IS series look especially close to what was in some of the aftermarket fans. I havent looked up specific part numbers for pricing. Have to do a fan replacement soon, so I'll be forced to look into it. Big thing is that it needs to be overspeced or heat sinked to last longer than the stock resistor in the situation where the fan doesnt spin up quickly and causes surge current through the resistor that's so fast the fuses are too slow to protect it. Thermal shock also in cold start with high inrush through the resistor. I always seem to blow fans and/or resistors when I forget to turn the fan off when starting the truck.
https://www.ohmite.com/high-power/
 
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NPT90

Well-known member
I don't know that I wouldn't use something like this
Cheapo fleabay

And just bypass the resistor in the box. I mean it's nice and neat in there and all it's just silly expensive
 
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