R

Rorie

Active Member
I've stripped down my heater box to blast and paint it.

The small plate which holds the 'heater resistor' fell to bits, so I removed the screw holding the resistor and it fell apart too. I wasn't concerned as I figured i'd just buy a new one, until I noticed that for some reason, it cost £130!

Photos below show my unit prior to it falling apart.

I've seen threads about replacing with a £3 resistor. But, can anybody explain how to do this? What exactly does this resistor do? I read a few old threads (2015) saying someone was making kits and putting them on ebay, but I cant find any listings now.
Screenshot_20180822-075018_Chrome.jpg
20180821_185729.jpg

Any help appreciated.
ahlxga2a.gif
 
The resistors primary function is to drop the voltage to the motor when you select slow fan speed. You would need to know what resistance a normal one is before replacing it and preferably the motors current (so you can work out the power rating required).
Just be wary that the equivalent part in some Vauxhalls has been blamed for setting cars on fire so proceed with a bit of caution
 
Just another fine example of Land Rover design. I may have a spare in my stock pile if interested.
 
I took out the securing screw and it all fell apart! The wire on the resistor is still intact, so hopefully I can measure that tonight and get a replacement.

I assume it is only housed in the air intake as a cooling aid for the resistor?

My understanding is that the control lever on the dash has a sliding resistance to control the motor, so this would then be an inline resistor for the motor? Which looks to be the case based on the wiring …?
 
Does anyone every use low fan speed, mine is always either off or full on.

You will most likely find a full second hand heater/fan unit on ebay for around £40 - £50
 
Last edited:
The dash lever is just a three position switch, off, low and high speed. Mine is always on low.
You could replace the lever/switch and resistor with a variable speed resistor and have any speed you like between off and full.
 
tottot said:
The dash lever is just a three position switch, off, low and high speed. Mine is always on low.
You could replace the lever/switch and resistor with a variable speed resistor and have any speed you like between off and full.
Click to expand...
Mine is always on low too, however to replace it with a potentiometer / variable resistor would require a physically massive one to be able to manage the power & heat. A better option would be to use some sort of transistor / mosfet based variable power supply which could be controlled by a normal sized potentiometer, that said, you would need to know the motor specs (or measure them) to get the right one.
 
Ah, so despite it looking like I have a huge range of setting, it's actually just off, low or high?!

I measured the inline resister and it's 3.5 ohms. So I'll get a replacement ordered up.and all should work fine
 
Just had a look at the wiring diagram and it says that the resistor is 10 Ohms and that the motor is rated at 1 amp but protected by a 15 A fuse! Resistor seems reasonable but a bit suspicious about motor rating!
 
Rorie said:
Ah, so despite it looking like I have a huge range of setting, it's actually just off, low or high?!

I measured the inline resister and it's 3.5 ohms. So I'll get a replacement ordered up.and all should work fine
Click to expand...
!
 

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ah , so it does...

Comments on old posts i've found say things like:

"should only need a 1 or 2 ohm power resistor in series with the fan. (must be in the airflow before the matrix to cool the resistor)"

"I replaced my blower resistor with a 50w aluminium cased power resistor" ... "There was nothing wrong with my blower, other than I wanted to increase the slow speed slightly."

- at 50W, assuming 12v, that gives 2.9 ohms.

"I have used a 3 Ohm 100W aluminium clad wirewound resistor in my series fan to give two speeds."

So the only things i can find discuss low resistance...much lower than is noted in the wiring diagram.... And my measurement over it just now shows 3.5ohms
 
Some basic electrical theory and very rough calculations based on a bit of guess work and your 3.5 ohm reading.
We will assume that normal operating voltage is 14 v rather than 12 v (as the alternator will be charging the battery)
Assume that the motor gets say 6v at low speed (could be more or less, just a guess at the moment)
That means the resistor needs to drop about 8 volts (14 - 6)
To drop 8 volts over a 3.5 ohm resistor requires a current of 2.3 amps. (8 V divided by 3.5 ohms).
Heat needed to be dissipated by the resistor will be 18.5 watts (volts x amps = 8 x 2.3) or (current squared x resistance = (2.3 x 2.3) x 3.5).
In theory anything with a power rating over 20 watts would work in this scenario however you also need a sufficient heatsink area to dissipate that heat efficiently.
If anyone knows the actual voltage on slow speed you can change the figures above to recalculate the minimum resistor wattage.
 
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