tpenta

Hi gang,

I have a 997 and I posted a problem there but I didn't get much information. I'm hoping someone from the 996 crowd may have more info on this:

I noticed last week that while the AC is on, the passenger radiator fan is blowing at full speed but the driver's side fan doesn't seem to be on. Also, when I turn off the AC and the car is still on, the passenger radiator fan still stays on.

Any ideas? Someone suggested there may be a relay or fuse issue but I don't know how to check either.

Thank you.

-T

ivangene

on = low or high speed?

If high they make quite a bit of noise.

The low speed (if the same as 996) gets the same power but the power is diverted thru a ceramic resistor. The resistor gets hot and when water (from driving or whatever) contacts the resistor, it can fracture internally and fail. when this happens the fan will not come on at low speed but will still come on at high speed (when engine temp is very warm .... I forget the exact temp)

SO in the 996 you can jump the relay and test the fan to see if it works and if so test the power to see if it gets power on low speed thus confirming the resistor (highest suspect part)


the resistor is soldered in place so changing is on a 996 is a bit of a pain but can be done without removing the front bumper - IIRC Porsche sells a new fan with resistor on it for some huge amount of money, but if you can prove it is the resistor and are handy, you can just replace that for under $100 (again, on the 996)
Ed

ivangene

LINKY LINK

here is where I got my info... good pics and explains the jumping (which was done for emergency operation in this write up but also diagnoses the resistor or fan as being the problem)

Pac996

Do you have a value for the resistor and picture of location. I just happen to be a ham radio operator that smokes all types of soldier

smackboy1

It's called a "series resistor" or sometimes referred to as a "ballast resistor". I believe the part # is 99661610100 and is around $60 from Sunset. There are a bunch of posts on Renntech.org, some with pix. Just do a search under those 2 terms.

ivangene

I have thought about just using a 944/924 resistor which cost $20... I mean as long as it reduces the current and runs slow speed... who cars if it is 500 rpm or 527 rpm right??

tpenta

Thanks everyone. I'll look into this.

The fan stays on even when the car is stopped in the driveway. Even after a cold start, if the AC is on, the passenger fan comes on at full blast and stays on even if I were to turn off the AC. Nothing coming out from the driver-side fan, although it might be working at high speeds. I wouldn't know.

Thanks again.

-T

tpenta

Hi gang,

I thought I'd post an update here in case this is referenced in the future.

Just had the car cheked out and was told the codes are all normal and the fans work appropriately. Apparently, as was perhaps mentioned in this thread, each of the fans serves a different purpose and they do come on at different times. Also, the AC fan does stay on for a while even after the AC is turned off.

FYI,

-T

smackboy1

Who checked it out, the dealer? I had a similar issue where one fan would come on differently than the other fan. I asked the dealer to examine it and they told me that was "normal". But I didn't believe them and did my own research and lo and behold, it wasn't "normal" at all, the series resistor was fried on that side. Sometimes a technician will just read the scanner and if no error codes, assume everything is OK. For your own peace of mind I would check out other 997s as yours and confirm that their fan operation is the same as yours.

Zookie

im preety sure a CEL would come on for that...

thklinge

The cooling fan control is pretty simple in the 996/986 (and possibly 997/987).
The DME controls the fans via four relays in the front driver footwell. It draws a signal from a coolant temperature sensor in the engine. If your needle moves like it should in the instrument panel, both the DME and the temp sensor is doing its job. If the DME gets proper readings from the sensor it WILL NOT throw a CEL (Check Engine Light) and no error codes will be written. The DME doesn't know if the fans run or not, at what speed they run or what the temperature is in each of the radiators. Heck, the whole front end could be missing and the DME wouldn't know about it until it ran out of coolant and overheated.

Back to how it works: With the car at low to normal temperature (below 185? not sure of the exact temp) and the A/C off, the fans do not run at all. If you enable the A/C, the fans will come on at low speed. Low speed is enabled by the DME telling two relays in the footwell fusebox to turn on. They put out 12V that goes to the fan, but instead of going directly to it, it's routed through two resistors mounted on the frame that holds the radiators to the car. These resistors reduce the voltage and allows for a quiet low-speed running of the fans to cool the aircon condensers, mounted ahead of the radiators. These resistors get quite hot while in use. They are mounted low and without cover so when driving in the wet cold water will splash over them they have to endure serious temperature changes that eventually breaks them internally. When this happens the fans will not run at low speed.

When the car runs hot it will enable two other relays (one for each side) that give the fans +12V directly. The fans hit full speed (you'll hear them loud and clear, even inside the vehicle!), cools the coolant down and then shuts off.

There are a bit more to it, with a fan in the engine compartment, and valves that enable/disable coolant flow to the radiators, but that's a topic for another day.

ivangene

this is a year old ?

but good info

thklinge

Yeah, didn't notice the age of the thread before I posted. And when done I figured it was useful to have on here anyways. Sorry for the revival.

RPMulli

Hey my drivers fan was not working before and I ended up pulling the fan apart and found that the motor brushes were all corroded and seized up. I just cleaned them off and the fan ran like new afterwards.

ivangene

OT - Ride, I really like your new avatar