View Full Version : Resistance values for heater fan resistors?
I've got that standard problem that my low fan speed doesn't work. It eventually got to the top of the list of things to do and, when I got the assembly out, the low fan speed resistor just fell to pieces in front of me.
Question is does anyone know what the resistance values of the four resistors are? Oh, and what wattage they see?
I was gonna just buy another one from Toyota and then thought,there's got to be a nicer way to do this than four coils of bare wire, surely?!?
Frmo memory its only something like 2 ohms 1/4 watt.. but a 1/2 watt cant do any harm :D
wire wound is preferable i think.
lplpaca
13-06-04, 12:26 AM
You can pinch them out of old broken radios / tv's - the big white oblong ones, have a ceramic coating tp dissipate heat so no more failures, or bare wires, or if you have any money left from the rest of your repairs / mods to your supra you can get from the likes of Maplins, Radio Shack, any good radio/electronic spares shops in your area!
Paul C
beninsupra
13-06-04, 12:36 AM
I think someone on the Smartgroups forum posted the value as being 1.4 ohms. I just got some high-power resistors from Maplins and connnected them up like this:
http://homepage.ntlworld.com/p.freeman60/Supra/IMGP1603.JPG
They're three 4 ohm resistors wired in parallel which is the same as 1.33 ohms. I actually found putting them side by side like this meant that they wouldn't fit back in the duct, so I had to move one of them round to make a kind of triangle if that makes sense (couldn't be bothered to take another photo!). You might be able to get away with just one resistor of the right value, but I decided to use three to be one the safe side as they do get pretty hot.
It works perfectly like this, and the resitors were about 20p each.
HTH,
Ben
The whole point about them being open wire coils is that they will vary the resistance depending on the temperature of the surrounding air. If you replace them with fixed resistors this is not going to be the same effect.
The whole point about them being open wire coils is that they will vary the resistance depending on the temperature of the surrounding air. If you replace them with fixed resistors this is not going to be the same effect.
Hi Lofty, sorry, I'm not sure I understood correctly, it seems that your saying that that the fan is intended to change the speed it runs at because the ambient temperature of the air will affect the resistance of the resistors but surely the major change to the temperature of the resistors is due to the current running through them, isn't it?
they do get pretty hot
I assumed they were open coils to help them to stay cool?
They're three 4 ohm resistors wired in parallel which is the same as 1.33 ohms. I actually found putting them side by side like this meant that they wouldn't fit back in the duct, so I had to move one of them round to make a kind of triangle if that makes sense (couldn't be bothered to take another photo!). You might be able to get away with just one resistor of the right value, but I decided to use three to be one the safe side as they do get pretty hot.
It works perfectly like this, and the resistors were about 20p each.
Ben, do you seen any change to the way the fan operates in low mode versus mid and high mode since you did your mod?
The whole point about them being open wire coils is that they will vary the resistance depending on the temperature of the surrounding air. If you replace them with fixed resistors this is not going to be the same effect.
Not for fixed low/med/high fan speed running. They just clamp down the ohms to the blower motor, and are not temperature sensitive.. The temperature sensitive running is controlled by a different circuit AFAIK, using two temp sensors & the solar sensor in the dash (little black cube just under where you put your tax disk is the solar sensor; the vent just above the glove box is the cabin temp sensor.. not sure where the ambient temp sensor is though!)
Not for fixed low/med/high fan speed running. They just clamp down the ohms to the blower motor, and are not temperature sensitive.. The temperature sensitive running is controlled by a different circuit AFAIK, using two temp sensors & the solar sensor in the dash (little black cube just under where you put your tax disk is the solar sensor; the vent just above the glove box is the cabin temp sensor.. not sure where the ambient temp sensor is though!)
I sort of agree with that statement, but you have to ask why they are designed in this way. Why didn't they just use large wire-wound resistors instead? Resistance will vary with temperature and Ohm's law tells us that with a fixed voltage and a varying resistance the current must alter, therefore the fan speed must also vary slightly. I guess not everything on the Supra is well designed though, and this could just be another example.
The ambiant temperature sensor is mounted in the bumper grille on the passenger side, next to the intercooler.
I sort of agree with that statement, but you have to ask why they are designed in this way. Why didn't they just use large wire-wound resistors instead? Resistance will vary with temperature and Ohm's law tells us that with a fixed voltage and a varying resistance the current must alter, therefore the fan speed must also vary slightly. I guess not everything on the Supra is well designed though, and this could just be another example.
The ambiant temperature sensor is mounted in the bumper grill on the passenger side, next to the intercooler.
I agree that the coil arrangement is pretty wierd, but suspect it's down to a friday afternoon design after too much saki :) (bit like the myriad of different switch types, or the totally bizarre driver's window switch)
I'll root in the trsm wiring diagrams too see just how the auto system actually controls the fan speed.. i don't think it takes the coils into account though,as i'm pretty certain i saw a motorised potentiometer somewhere which would do the job..
beninsupra
14-06-04, 09:47 PM
I'm also kind of doubtful that the resistors have anything to do with varying the fan speed dependent on temperature. I suspect this arrangement is just very cheap and a good source of revenue for Toyota. Of course, it's always nice to do things properly and I did look into buying some resistance wire, but Maplins only have one sort which is v. pricey and you'd need loads of coils in order to get the required resistance.
I decided to use three resistors to be on the safe side as the max wattage resistor you can get is 10 watts, and so using 3 = 30 watts which I'm sure must be adequate. The only problem I envisaged after I'd soldered it all up was that I might be putting a bit of large physical restiction in the air vent, but it doesn't seem to have made any difference at all and blows out air just as it used to on the higher speeds (I bought the car with speed 1 already knackered so can't vouch for that but it seems fine now).
I suppose that I could measure how many amps it's drawing with a 1.33 ohm restriction thereby working out the watts (= V x A) and therefore the minimum number of resistors needed (may only be one in actual fact, especially with the cooling effect of the air). One resistor certainly wouldn't pose any sort of airflow restriction at all.
Ben
The more I think about it, the more I think that you guys are right. The resistor pack will need to dissipate a large amount of heat. Ceramic enclosed resistors will get hotter than open wire coils. Ben's repair demonstrates how much wire is required and what better way to fit a long piece of wire into a small space that coiling it?
:notworthy
OK, I did this mod about 2 weeks ago now.
I used one of those brass encased resistors with the heat sink bolt downs. It's a 1ohm 10watt jobby. I deliberately left the fan on 1 for the first week and it didn't burn out (it did stink for the first day though!). Cost me £3 fom our local radio repair shop.
OK, I did this mod about 2 weeks ago now.
I used one of those brass encased resistors with the heat sink bolt downs. It's a 1ohm 10watt jobby. I deliberately left the fan on 1 for the first week and it didn't burn out (it did stink for the first day though!). Cost me £3 fom our local radio repair shop.
Excellent! do you have a pic/part no. as I need to do mine sometime.. :)
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