22 replies to this topic

[jd lj]

I'm in the process of reassembling my car and connected the power a fortnight ago. After doing so and checking that everything works I found that the interior fan only works on the high speed and not on low.
Prior to starting the resto I didn't have this problem so I have my doubts that it is caused by the switch which logically you'd expect to be the fault. I also tried my spare switch and had the same problem.

I plan on checking all the terminal connections again but is there anything else that could be the culprit that I should be checking?

[TOERUNNER]

Resistor is my guess

[jd lj]

Where do I find that? Excuse my lack of electrical expertise.

[jd lj]

I'm thinking out loud here but I could test the spare fan motor I have but without removing the heater box.

[S pack]

James, have a look up under the dash on the passenger side. You will see one of the wires leading to the fan motor goes to a wiring connector that plugs onto two male spades protruding down through the panel.

That is the resistor mounted into the heater box base plate.

 

Test a spare heater motor on your car. If the low speed still doesn't work then either the fan switch or the resistor or the wiring is faulty.

[jd lj]

Ok, I know the resistor in the heater box that you're referring to.
As I mentioned previously the switch was working previously and I've tried a second switch. But I'll go through the suggestions above and report back.

Thanks

[jd lj]

So after looking at the wiring diagram I saw that it looks like in one of the switch positions power to the fan motor has to go through the resistor wire element in the heater box first. I figured that if I unplug the wires from the resistor and join those 2 terminals with some wire and bypass the resistor I could test it that way. Doing this the fan works in both switch positions but the speed sounded equal.

Judging by the wiring diagram the resistor will only heat up to help with the demisting in the low position.

It looks like I'll have to take the heater box out to rectify this, bugger.

[TOERUNNER]

So after looking at the wiring diagram I saw that it looks like in one of the switch positions power to the fan motor has to go through the resistor wire element in the heater box first. I figured that if I unplug the wires from the resistor and join those 2 terminals with some wire and bypass the resistor I could test it that way. Doing this the fan works in both switch positions but the speed sounded equal.

Judging by the wiring diagram the resistor will only heat up to help with the demisting in the low position.

It looks like I'll have to take the heater box out to rectify this, bugger.

The resistor reduces voltage  to the fan to slow it down in the low position. it has nothing to do with the demister, get a multimeter and check the ohms reading across the terminals of the resistor and if it is open circuit the resistor is rooted.

[TOERUNNER]

So after looking at the wiring diagram I saw that it looks like in one of the switch positions power to the fan motor has to go through the resistor wire element in the heater box first. I figured that if I unplug the wires from the resistor and join those 2 terminals with some wire and bypass the resistor I could test it that way. Doing this the fan works in both switch positions but the speed sounded equal.

Judging by the wiring diagram the resistor will only heat up to help with the demisting in the low position.

It looks like I'll have to take the heater box out to rectify this, bugger.

The resistor is there to reduce voltage to the fan motor so the fan runs slower. 

[jd lj]

Yes, I also wondered if the fan speed was higher with my wire being thicker than the resistor wire.

Previously I had assumed that the resistors was intended to heat up when current passes through it due to being such thin gauge wire and then the fan would use that heat for the demister, but it didn't make sense why there's no connection to the heater controls. As I said I'm no auto electrician. But I've learnt a bit more today. Thanks.

[Heath]

If the "resistor" wire is broken, it would cause this problem. Checked continuity?

 

On my LH/LX loom that I started off with to wire my Torana, the only real damage it had on the main harness was that a resistor wire (the 9V points ignition supply, not the low speed fan in this instance) was absolutely rooted. It had been hot, and all the insulation was compromised, it was cracking away etc.

 

So I concluded that the service life of a "resistor" wire can certainly be shorter than regular wires around it, due to it heating up more etc. (I am also no auto electrician)

[claysummers]

Sounds pretty obvious that the resistor is open circuit, needs replacing or bypass. If anyone knows the rating you can get a replacement from somewhere like Jcar and wire it in.


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[Bruiser]

So after looking at the wiring diagram I saw that it looks like in one of the switch positions power to the fan motor has to go through the resistor wire element in the heater box first. I figured that if I unplug the wires from the resistor and join those 2 terminals with some wire and bypass the resistor I could test it that way. Doing this the fan works in both switch positions but the speed sounded equal.

Judging by the wiring diagram the resistor will only heat up to help with the demisting in the low position. It looks like I'll have to take the heater box out to rectify this, bugger.

You could try to jump the low speed wire to the non-resistor high speed fan lug on the fan box connectors
if that’s not what you described just then
the switch will put 12 v onto either wire. If you reverse them, high becomes low and versa visa
This would eliminate the switch being the problem without doubt.
Then it has to be the resistor.
You could put a pot in the high speed wire and have a variable speed adjustment,
at the appropriate resistance value, of course.
Just where to drill the hole in your dashboard is the problem

If the fan sped up, it could have been that the extra wire thickness lessened an bit of a voltage drop,
if there was one already
and higher voltage at the other end sped your fan up
I reckon you’re onto it

[Rockoz]

You could try to jump the low speed wire to the non-resistor high speed fan lug on the fan box connectors
if that’s not what you described just then
the switch will put 12 v onto either wire. If you reverse them, high becomes low and versa visa
This would eliminate the switch being the problem without doubt.
Then it has to be the resistor.
You could put a pot in the high speed wire and have a variable speed adjustment,
at the appropriate resistance value, of course.
Just where to drill the hole in your dashboard is the problem

If the fan sped up, it could have been that the extra wire thickness lessened an bit of a voltage drop,
if there was one already
and higher voltage at the other end sped your fan up
I reckon you’re onto it

Finding a 'pot' with a good enough current rating may be difficult.

Few I have encountered over the years would handle the current required for more than about half a millisecond before they let out their smoke.

 

If you check on ebay for nichrome resistance wire you could make your own resistor.

Just need to find the resistance of the original part, then wind one up to the same resistance.

There are various ohms/foot values to choose from with a good supplier.

 

The problem may also just be one of the resistor connections. 

But you will have to obviously access it to find out.

 

Cheers

 

Rob

[dron]

Hi

    There are a lot of fan resisters out there, Most AC repaireres or auto elec's should be able to find something that will work, May not be the exact thing but not hard to mount one with 2 screws into the heater box and wire it in.

I know that the higate caterlog lists several generic resisters. They will not sell to the public so back to needeng to go to an auto electrical place. A random lenght of wire or a resister from Jaycar may not be a good thing, If it is not up to the job the magic smoke may come out. Then again it may demist the window as things burn I guess

[jd lj]

I pulled out my spare heater box from under the bench in the shed and noticed that the resistor is firmly mounted to the base plate but on the one in the car it's not so firm and pushes up a bit but then springs back down. I'll run some wires to test the resistor in the spare heater box and then if I have to I'll pull the heater box out and swap the resistors over. Obviously I'm really not keen on pulling out the heater box and then refitting it but it'll annoy me later if I don't. I'm not a fan of compromising.

[VDO]

You don't need to remove the heater box to replace the resistor pack.

Just switch the resistors over.

[jd lj]

I removed the heater box this morning and removed the resistor. One end of the resistor wire was no longer connected. I took the resistor from my spare heater box and swapped it over and refitted the heater box and now it's all working as it should. I was reluctant to do this job but it only took about 1.5 hours all up but would've annoyed me down the track if I hadn't.

I don't think that you could replace the resistor without removing the heater box as you wouldn't be able to access the rivets that need to be drilled out.

[S pack]

I removed the heater box this morning and removed the resistor. One end of the resistor wire was no longer connected. I took the resistor from my spare heater box and swapped it over and refitted the heater box and now it's all working as it should. I was reluctant to do this job but it only took about 1.5 hours all up but would've annoyed me down the track if I hadn't.

I don't think that you could replace the resistor without removing the heater box as you wouldn't be able to access the rivets that need to be drilled out.

.

I'm not looking forward to pulling my heater box out to replace my wiper motor.
 

[jd lj]

The trick to accessing the two nuts on the drivers side is to lie on your back in the passenger and with the center console removed use your left hand/fingers to reach them that way. I wanted to rectify this before I put the passenger side seat back in.

[73SUNBURSTEXYOUWON]

.
I'm not looking forward to pulling my heater box out to replace my wiper motor.
 

Just dont drive in rain Dave, she'll be right mate.

[S pack]

Just dont drive in rain Dave, she'll be right mate.

The Preslite still works but she is like me, getting older and slower.
 

[Glacier73]

Recently had to pull my heater box out to replace the passenger side wiper pivot, found removing the two nuts on the studs of the drivers side the most difficult part of the job, found it best to remove the drivers seat to allow better access so could lay on my back and be directly below it, flexy extension for socket also helped.