effects of a bad cooling fan resister. - 986 Forum - The Community for Porsche Boxster & Cayman Owners

mountainman · 04-08-2014, 08:17 AM

Just did a durametric check of my cooling fans on the 04 boxster S. Both fans worked on high and only the right on low. Switched low speed relays and nothing changed. I assume the ballast resister is bad on the left side.
My question is what effect will it have on anything if I can't get it fixed for a while. Will the high speed fan just come on quicker to cover for the inoperative low speed or is there another effect. It may be a while before I can get to replacing the resister.

Steve Tinker · 04-08-2014, 03:30 PM

Usually, when the ballast resistor fails on the lower setting, the fan will not run at the slow speed - it does not revert automatically to the higher speed.
So your car will be left operating on one fan @ the slow speed, but if you think your temps are maybe too high, switch on the A/C which automatically reverts fans to high speed.

mountainman · 04-08-2014, 03:49 PM

Quote:

Originally Posted by Steve Tinker

Usually, when the ballast resistor fails on the lower setting, the fan will not run at the slow speed - it does not revert automatically to the higher speed.
So your car will be left operating on one fan @ the slow speed, but if you think your temps are maybe too high, switch on the A/C which automatically reverts fans to high speed.

I didn't think it would automatically go to high speed because the low speed was inoperative, but assumed that if the temperature started toclimb because the low speed wasn't working that that would cause the high speed fan to come on and maintain the temp at normal. I have not noticed any increase in operating temp and I have no idea how long it has been inoperative. I will of course replace the resistor asap and as suggested can run the ac if need be.

mikesz · 04-09-2014, 04:23 AM

My right fan wasnt working at all and binding. Caused fuse to blow and melted part of my fuse block. I wound up swapping out both fans. My left one like yours only worked on high speed. Probably could have gotten away with replacing the resistor but I had the car apart anyway and cleaned the radiators while I was at it.