Radiator fan resistor rating? (Page 1/2)
CSM842M4 MAR 16, 06:39 PM
I've read on this forum about the value of wiring around the low-speed resistor for the radiator fan. And in time, I may do exactly that. But, in the meantime, let's argue that, for whatever reason, a guy wanted to replace the resistor to keep the low speed. If that were the case, does anybody know the resistance of the original resistor? Or a stable source for them that doesn't want one of your offspring in exchange ( hold on just a minute...)? Seems like that guy could substitute an ignition coil resistor from an old points-type ignition and get the low speed back, if the resistance were close to the same... Any intel or experience in this area would be appreciated; thanks in advance - Chris
theogre MAR 16, 10:42 PM
OEM is like old type ignition resister but different value.

See my Cave, Rad Fan

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

[This message has been edited by theogre (edited 03-16-2019).]

darbysan MAR 17, 10:49 AM
I run dual fans on my Elky. On low speed, they run in series, in high speed in parallel. Since the series solution works on low, then I would think if you measured the resistance of your fan without the resistor, and bought that OHM resistor to use on the Low circuit, you would be good to go. It should be something pretty low- 1-2 Ohms, probably. It takes a pretty healthy resistor to survive. It needs to dissipate a lot of heat, and could be a fire hazard if the correct resistor is not used. GM used them in a lot of vehicles in the 80's when Electric fans were just coming into fashion.

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'87 GT , '00 3800 Series II SC, 4t65e, Vue Power Steering. (SOLD)

CSM842M4 MAR 17, 12:46 PM
Thanks,Ogre and darbysan. I might be able to measure the resistance, but i have my doubts since the resistor itself is now a 2-piece affair. Yes, it looks for all the world like a ballast resistor for a points ignition, but the ceramic base has broken in half. Ogre's rad fan cave says resistance should be somewhere between a third and a half an ohm. Everything at my FLAPS that we stock shows 2 ohms minimum. Guess I'll do some shopping with the usual suspects first, then hit ebay and the Rock.
theogre MAR 17, 06:49 PM
OEM spec is 0.3Ω 50W
Even now many others not just GM have two speed fans w/ resistors close to same fraction of Ω mounted somewhere on fan assembly and all I've seen are high watt, 50w or more, and uses fan air to cool it. Many current cars also have 1 time thermal fuse at/in the resistor to kill power if fan doesn't run to cool them because will "melt down" and can cause a fire because most are mounted in/on some type of plastic.

Aluminum case resistors are often smaller but Most need extra heat sink beside case case and/or a lot of force air flow to get listed power rating. Most will fry w/o that at 1/2 watts listed or less. Is why Many fools have melted things or worse using power resistors when installed LEDs for not having something to heatsink and air to cool them.

You likely never see them for Fiero at auto parts store including RA. Digikey and others yes. Do not buy them from Ebay etc because many won't last even if you get right value. Fan Power is only protected by a fuse link and car can burn down w/o blowing the link from fan motor or resistor problems.

[This message has been edited by theogre (edited 03-17-2019).]

pmbrunelle MAR 17, 10:43 PM
I've never actually seen a radiator fan resistor in a Fiero... so this suggestion may not work whatsoever.

Anyway, I found this on Digi-Key, PN A137255-ND:
https://www.digikey.com/pro...J/A137255-ND/5587161

I like it for its threaded terminals (works with ring terminals). I don't know how it would physically fit though.

Ogre is right; these aluminium-bodied resistors need to be derated when not bolted to a heatsink. At 300 W though, it should work.
darbysan MAR 18, 10:00 AM

quote
Originally posted by CSM842M4:

Thanks,Ogre and darbysan. I might be able to measure the resistance, but i have my doubts since the resistor itself is now a 2-piece affair.



My suggestion was to measure the resistance of the Fan Motor only ( not the existing resistor). Duplicating the Motor's resistance with a resistor would result in 1/2 speed when used in a series circuit. Looks like Ogre has the actual value available, so no need to do this step now.

And I agree, using any resistor without proper cooling is just a fire waiting to happen. I have a 2 speed fan on my SSR, and the resistor is huge. Note that it is placed to receive cooling flow from the Fan. See Picture.
darbysan MAR 18, 10:04 AM
Another option is to upgrade to the Volvo 2 speed fan. Doesn't use any external resistor. Cost for a new one from Amazon is less than $100, and they work great. I put one in my 3800 swap project, and was very pleased with the performance. Since you already have the relays, etc for 2 speed operation, wiring would be a breeze.
http://www.fiero.nl/forum/Forum2/HTML/121712.html
theogre MAR 18, 12:05 PM

quote
Originally posted by darbysan:
My suggestion was to measure the resistance of the Fan Motor only ( not the existing resistor). Duplicating the Motor's resistance with a resistor would result in 1/2 speed when used in a series circuit. Looks like Ogre has the actual value available, so no need to do this step now.

And I agree, using any resistor without proper cooling is just a fire waiting to happen. I have a 2 speed fan on my SSR, and the resistor is huge. Note that it is placed to receive cooling flow from the Fan. See Picture.

Pic is so small can't see the resistor.
Resistor used by Kia and others... Often in a corner of fan shroud...
CLICK FOR FULL SIZE

white part is hollow to increase heat removal.

Motor + resistor does not = 2 motors in series. Measure Ω w/ any normal meter on motor is useless for this for several reasons and beyond simple posting.
Motor will see the resistor same as in my Cave, Electric Motors
If you have wiring problems too... can fry the fuse above, the resistor w/o a fuse like Fiero has, any relay controlling the motor, and/or motor itself.
Is likely why many 84 Fiero's w/ AC have fried resistors. Many others have fried Fan Relays for same reason.
When fixing the motor etc on that circuit, you should check power on red wire and all grounds in front of car too. Check power when motor is on and off w/ engine running and check power in back as ref to see problems. Example: V in back say alt output to frame = 14.6 but V to Motor On @ relay output(s) to frame = 12 then you have other problems. That can be iffy wires, grounds, or likely both.

Before you asked... No I can't tell you what fuse are used in above pic. Dirt and minor corrosion remove any fuse marks. Resistor has no marks either. Quick guess is ~ same Ω and maybe a bit more Watts because of shape. I didn't bother to measure Ω because most meters can't read < 10 Ω reliability, more so < 1 Ω.
87convert JUN 18, 08:47 PM
Just ordered a replacement for this resistor from GMPARTSGIANT.com. GM part number 22049799. Still in stock. $75 shipped.

Rolland