What is correct gap for blower resistor contacts ?

DCred911SC · 04-19-2005, 04:42 AM

Can anyone help out here please ?

The fresh air blower on my SC works at max speed on position 1, the correct speed on position 2, and max speed where it should be (position 3).

I have removed the fan unit and it appears that the speeds are controlled by a resistor block, which I have also removed. Looking at the resistor block I gather that the resistors are cooled by airflow from the fan, and if they get too hot, the contacts close putting the fan on full speed and thus increasing airflow.

Looking at the pics below, the contacts for speed 1 have closed up (probably by rust and age). Does anyone have a spare fan unit where they could take a look at the resistors and give me an idea of what the gap should be for both speeds 1 and 2 resistor contacts

Thanks a bunch

David C

seventyeight911 · 04-19-2005, 06:19 PM

can you move the contact points apart to see if they are welded together?

DCred911SC · 04-19-2005, 11:59 PM

Yes, I can move the contacts apart. No welding together, they part freely.

Split50 · Split50's Garage

No help here I'm afraid but my car did exactly the same thing, max on speed 1 & 3 then after a while 1, 2 & 3.
I hope you get an answer soon as the blower is too loud to use.

Tim

seventyeight911 · 04-20-2005, 07:41 AM

where is this part located so i can remove mine?

Hugh R · 04-20-2005, 09:13 AM

Quote:

Originally posted by seventyeight911
where is this part located so i can remove mine?

Smugglers box

Mysterytrain · 04-20-2005, 10:17 AM

Just a thought but shouldn't they both be open. It looks to me like they are meant to close if the coil (resistor) gets too hot. Looking at the picture there is nothing that would would make the contacts work except for heat. I'm guessing they work as follows..resistor 1, the big one would be the slow speed. Resistor 2 would be the middle speed and no resistor would be high speed. It appears that the contact is shorting out resistor one..so you are getting full voltage to the blower. The contact arm on resistor two appears the be straight..I'm seeing a curve on the first resistor's contact blade. I would measure the gap on the other side and do some cleaning and bending.

PeterTarga · 04-20-2005, 10:47 AM

Hi,

I also have a problem with the fresh airblower, he is always on speed 3, the two metals that make a short circuit over the resistors must be bi-metals, and after a long time, like mine and this SC, the function of the bi-metal is lost, so i believe that you should replace this part by a new one. I looked already for a new part but i couldn't find one.

Peter

john walker's workshop · 04-20-2005, 12:27 PM

they're circuit breakers, like in many headlight switches (other than 911s). they should be closed in normal use.

DCred911SC · 04-21-2005, 01:47 AM

seventyeight911 - The resistor block is located in the air duct of the fan housing. Once the fan housing is out, this is what you need to do

1. disconnect the electrical spade connectors from the motor.
2. remove the butterfly flap on the fan housing air outlet (nearest the resistor block.
3. remove clip from butterfly flap linkage and pull out mounting bar.
4. unscrew the two screws holding the resistor block into the housing.
5. The resistor block can withdrawn, albeit with a bit of patience out of the air outlet. It is easier to take out the grommet where the electrical wires go though the fan housing and then feed the wires through as the resistor block is withdrawn.

Mysterytrain - You're right, I could set the gap the same as the other one, but I'd rather try to get the factory settings if possible. If all else fails, I'll probably try that.

Here's another thought, if there are any electronics wizards out there, is it possible to replace these archaic resistors with the types used in circuit boards. The resistors are marked with 2.5 ohms (for speed 1) and 0.75 ohms (for speed 2).

Split50 · Split50's Garage

Looked at my PET cd, its called a temp switch
Pelican sells them for $67.52 as a special order item or you could probably get one from your local OPC

Tim

Mysterytrain · 04-21-2005, 07:14 AM

I installed some footwell blowers in my 78 targa and had to come up with a resistor setup to control the fan speeds. I , of course went the over kill route and used a 2.2 ohm and a 1 ohm 100watt aluminum housing power resistors that were about $15.00 each and about 3" long. They work great..but they aren't going to fit in your location. Personally, I would clean up what you have and tweek the blade. If you are planning to keep the car forever and use the blower often the original part might be a good investment before they are no longer available.

DCred911SC · 04-21-2005, 08:08 AM

Tim (split50) - can you get the part No from your PET CD ? Car is an 82SC

Thanks

Split50 · Split50's Garage

Hi David,

Thought I already had, obviously not!

911 618 151 00

Good luck

Tim

DCred911SC · 04-22-2005, 05:29 AM

In case anybody is wondering, I've ordered one one the local OPC. Cost was £42

jakz · 06-26-2013, 09:25 AM

reviving the old thread to ask if anyone found out if the resistor contacts are supposed to be closed? i just took out mine and was pretty rusted so i cleaned it but i cant make it work

best regards

theiceman · 06-26-2013, 10:05 AM

they are suppose to be closed ... the intention of the resistor is to take some of the load so the fans will run at different speeds. The resitirs are of course power resistors and give off large amounts of heat so are mounted in the air tunnel.
if something goes wrong and the resistor heats up too much the bimetalic switch will bend and seperate the contacts .. killing the power to the circuit until the resistors cool down.

When you are on full power there is no need for any resistors as all the power is going to the fan therefore they are all bypassed and usually works .. when checking these make sure you have good continuity between the contacts on the bench and at the connectors.

jakz · 06-26-2013, 02:28 PM

thanks iceman that made sense to me also but actually i made a test heating the resistors with a heatgun and when they get hot the switch closes because the coils compress when heated so having them closed all the time doesnt sounds right but i dont undersatnd a lot about this

does anyone know if the fan speed is regulated by the amount of "earth" on each contacto or are the coils in the resistors meant to get hot and close either one or both so earth would be tripled when fully closed?

i have no idea how this works but would like to understand so i can come up with a mod to make it work a little better

regards!

theiceman · 06-26-2013, 03:17 PM

Quote:

Originally Posted by jakz

thanks iceman that made sense to me also but actually i made a test heating the resistors with a heatgun and when they get hot the switch closes because the coils compress when heated so having them closed all the time doesnt sounds right but i dont undersatnd a lot about this

does anyone know if the fan speed is regulated by the amount of "earth" on each contacto or are the coils in the resistors meant to get hot and close either one or both so earth would be tripled when fully closed?

i have no idea how this works but would like to understand so i can come up with a mod to make it work a little better

regards!

wow i believe you but that makes no sense at all does it

i need to see a schematic .. what car are they off ?

jakz · 06-26-2013, 03:30 PM

Quote:

Originally Posted by theiceman

wow i believe you but that makes no sense at all does it

i need to see a schematic .. what car are they off ?

i know! thats why im having trouble figuring out

here are the diagrams from a 73, mine is a 74 but it looks almost the same

http://www.pelicanparts.com/911/911_Parts/Electrical/911_electrical_1973_CIS_Part2.jpg

http://www.pelicanparts.com/911/911_Parts/Electrical/911_electrical_1973_CIS_legend2.jpg