Front heater Rheostat (resistor) ???

camo westy

My 85 Weeekender has always (since I owned it) had one speed of heater fan - High---

I took out the heater today, figured I'd take a week and fix some electrical issues, including the heater rheostat replacement. Also finish the new 'Fear No Deer' steel bumpers (photos when finished next week!)

The usual suppliers have no source for the VW resistor (rheostat)

VW used the same switch and blower motor in Jetts/Golfs - any reason to not use the Jetta resistor and fid a suitable mount for it?

Thanks
Bates

Wildthings · Samba Member Joined: March 13, 2005 Posts: 52333

You don't need a rheostat, just a resister. One from another VW product or many other different makes should work is the resistance is similar.

zuhandenheit · Samba Member Joined: June 27, 2008 Posts: 897

A rheostat is like a variable resistor--a knob that produces greater or lesser resistance. The dash knob for the blower motor is not a rheostat: it's just a switch. If I remember correctly, it sends 12v either directly to the motor (this is 'high'), or to one of two routes through the big resistor, one of which lowers voltage more than the other (the resistor functions as two resistors in one part--one has a higher ohm rating than the other).

Vanagon Nut · Posted: Mon Dec 15, 2008 8:27 pm Post subject:

Is the resistor pooched?

My understanding is that it's usually the switch that fails first. And FWIW.......

Not suggesting it's the right way to do it, but when I rebuilt the air exchanger/replaced fan etc., since I was adapting the wires to the new motor, I extended the wires and mounted the fan resistor "outside" up by the rad (you can see the 3 wires going up at the RH end of the fresh air ram) for me, I figured it was a whole lot easier to get it if it fails.

Image may have been reduced in size. Click image to view fullscreen.

Someone elses idea, but makes sense to me. I assume the resistor gets hot at times, so I was careful where I mounted it.

Neil.
_________________
1981 Westy DIY 15º ABA
(VW Gas I4)

1988 Westy DIY 50º ABA

VE7TBN

morymob · Posted: Tue Dec 16, 2008 5:04 am Post subject:

Next time fan resistor goes out mine will be changed to the variable reostat type ,u get any speed u need and is off an older Plymouth car and flaps may carry simuliar ones.

morymob · Posted: Tue Dec 16, 2008 5:05 am Post subject:

Next time fan resistor goes out mine will be changed to the variable reostat type ,u get any speed u need and is off an older Plymouth car and flaps may carry simuliar ones.

ftp2leta · Posted: Mon May 04, 2009 9:02 am Post subject:

Any source for new resistor?

None at VW! GoWesty? Bus depot?

Thanks, Ben
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Vanagon Nut · Posted: Mon May 04, 2009 10:24 am Post subject:

If resistor not available, could a Jetta/Golf resistor be used?

I understand they use a similar/same fan.

Neil.
_________________
1981 Westy DIY 15º ABA
(VW Gas I4)

1988 Westy DIY 50º ABA

VE7TBN

Dogpilot · Posted: Mon May 04, 2009 2:05 pm Post subject:

You know, a while back this resistor discussion came up and others had pointed out the Jetta resistor to be the same values, it may not have the same form in mounting. I cannot remember (that neuron was sacrificed for some other bit of trivia) what the issue was, but it had been successfully used as a replacement. The switches are cheap and frequently the issue with the fan.

A rheostat would not really be a good idea for a couple of reasons. First it would be really expensive needing to handle 12-18 amps load. This means it needs to be able to shed a lot of heat, the reason the original resistor is on a ceramic substrate. The rheostat would get quite warm itself, kind of an alternate heating source on your dash. It also may not fit the dash, needing to be a large wire wound affair.
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Vanagon Nut · Posted: Mon May 04, 2009 2:22 pm Post subject:

Wildthings · Samba Member Joined: March 13, 2005 Posts: 52333

If you want variable speed, then what you want is some form of high amperage light dimmer that will work on 12VDC. Way less heat being generated than using either the stock resister or a rheostat.

Dogpilot · Posted: Mon May 04, 2009 4:55 pm Post subject:

Wildthings is on the correct path. You need a circuit that switches off rapidly varying the duration of the pulse to the motor. These run a lot cooler than the resistor brute force technique. These circuits also use a lot less power. Nickels mean so much to manufacturers so spending even a tiny amount more on parts means big losses for them. So until the cost of a switching circuit is cheaper than a switch and mondo resistor, they will continue to use the Flintstone technique of a switch and resistor.
_________________
Geology with a Syncro rocks!
86 Syncro Westy AKA "The Bughunter"
98 Disco I
08 Range Rover SC
08 VW Rabbit S
1951 O-1G

tencentlife · Posted: Mon May 04, 2009 4:55 pm Post subject:

Right, to do variable speed without the expense, bulk, and heating with consequent early demise of a true rheostat, you would want a Pulse-Width controller instead. They are out there, it's a much more common way of controlling a DC motor these days, but for the expense and complexity, three speeds is fine with me.
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OilNBolts · Posted: Mon May 04, 2009 7:37 pm Post subject:

High power PWM is a recipe for RF noise. Lots of harmonic content in that square wave. I think modern cars are doing it three-phase with a brushless motor, and varying frequency.
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tencentlife · Posted: Tue May 05, 2009 7:29 am Post subject:

Academic at this point, but we use many different solar controllers that are all PWM circuits, all at higher power than would be needed in this app, and far higher than that. None of them makes any RF that can be picked up on radio sets. A quality controller is not a problem in this regard.

Besides, the whole vehicle is a rolling RF generator.
_________________
Shop for unique and useful Vanagon accessories at the Vanistan shop:
https://intrepidoverland.com/vanistan/
also available at VanCafe.com!

Please don't PM here, I will not reply.

Experience is death to doctrine.


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