blower motor and resistor pack

[brandonvalentin]

Like most folks I've been dealing with the blower motor only works on setting 4 problem for a few years now, but I could usually clean the contacts on the resistor pack and get another winter out of it. This year the thing is finally dead, with one of the contacts actually breaking clean off. I need a new one. I also need a new blower motor, because it's got a short somewhere in it, probably as a result of the way in which the resistor pack failed. If I try to put 12V to it on the bench I just get some nice sparks.

Since the motor and resistor pack seem to be no longer available, what do folks do about this? Are these Bosch motors rebuildable or can I get a new one from Bosch somehow? And what about the coil pack? Does anybody make something solid state to replace it?

Looking for recommendations on what to do for 924S (early 944 NA style blower setup).

Thanks,

Brandon

[thomasryan]

Do you have one of those ceramic windings type resistors? This is what I use on rovers but you will have to mod the wiring. Range Rover A/C Blower Motor Resistor (Same Fit As Genuine Part # PRC8010)

[brandonvalentin]

Thanks, @thomasryan. I've managed to track down some super cheap used parts via eBay and I think at this point I'm going to try that option and if they don't work out I may have to deal with the local dealer and see if we can't track some down in Germany. If I'm going to have to mod something I'll just solder up something using pulse width modulation because these ceramic pucks are for the birds.

[thomasryan]

the part i posted is for replacing the cylindrical style that looks the same as the Lucas-mater-of darkness rover part...not the hockey puck style.

on a rover, it is mounted in the windshield cowl so low and medium speed only functioned when it rained.

[Bradical]

Originally Posted by brandonvalentin

Thanks, @thomasryan. I've managed to track down some super cheap used parts via eBay and I think at this point I'm going to try that option and if they don't work out I may have to deal with the local dealer and see if we can't track some down in Germany. If I'm going to have to mod something I'll just solder up something using pulse width modulation because these ceramic pucks are for the birds.

Can't use PWM on a DC motor unfortunately, DC doesn't have a frequency to modulate.

[brandonvalentin]

Originally Posted by Bradical

Can't use PWM on a DC motor unfortunately, DC doesn't have a frequency to modulate.

Sure you can, it works great!

You use PWM to introduce the modulation to the current. As long as the frequency isn't too low to keep the motor spinning, you're good. This is what modern cars do instead of the hockey pucks and resistor coils Porsche used on our cars. I'm sure something could be whipped with a 555 timer and a potentiometer (in the old rotary switch housing) pretty quickly. If the nasty old used one I've ordered doesn't work out, I have a feeling a trip to Radio Shack is in my future.

[Bradical]

What frequency? Direct current doesn't have a frequency. The motors would have to be AC for it to work- they may have them on modern cars, but they would have to be AC motors if that were the case.

For those reading this who don't know, PWM is converting AC current to a DC signal, and then modulating a second AC waveform by pulsing the output of the DC bus to the desired frequency which creates a fabricated AC signal. You would need an AC fan motor certainly otherwise you would just be turning the motor on and off rapidly, unless that's how you are saying it is done?

[brandonvalentin]

That's exactly how it's done. You're sending a square wave to the motor that constantly turns it on and off, but at a rate that's fast enough to keep the motor spinning.

[Bradical]

Wow, brilliant. So you would use the output of the 555 timer to run an SCR or something? How far can you go as far as current-carrying capacity?

[trinitrona]

Thanks to this thread I bought the Rover part thomasryan recommended. Do you happen to know off hand (or nearly off hand) how the wiring should be modified?

I've got wiring diagrams for both cars, but I'm having some trouble wrapping my head around what goes where since the rover part has 5 leads and the OEM resistor pack has 4 (I have an '87 924S with the cylindrical resistor pack).

[thomasryan]

look at this.

Splicing In New Resistor On Range Rover Classic

and this.

http://www.pelicanparts.com/944/electrical/944_84_AC_2.jpg

do you see how the resistance is daisy chained on the grounding side of the motor? the fan gets battery voltage and the switch varies the current level by the resistors in series.

I get..

1.) brown(stock 924) to brown(rover)
2.)br/wt(stock 924) to red(rover) this is speed 2----0.5 ohms
3.)br/ye(stock 924) to blue and one black(rover) this is speed 1----1.5 ohms
4.)br/bl(stock 924) to the other black(rover) this is speed 0----3.5 ohms

high fan speed bypasses the resistor pack and goes straight to the fan switch with no resistance to ground/earth. .

by connecting the on black lead to the blue (rover) you are effectively daisy chaining the resistors like the stock windings. if low is too low, compared to stock, move the black wire that you connected to the blue to the brown wire on the rover part to get only 2.0 ohms...which is probably closer to the stock resistance..check that.


clear as mud?

[trinitrona]

Thanks very much thomasryan! You've made it pretty clear to me and I appreciate the time you took to make it plug and play for me.

[thomasryan]

Right on. NLA sometimes requires a work around but Jim Ellis and ECS tuning shows 477 971 281 as still a viable part number.