Radiator fan not turning on when AC is off

[mark in sunnyvale]

Ok, I think I figured out what my temp gauge is going crazy. My radiator fan won't turn on when my AC is off. This causes my temp to go really high during stop and go traffic.

I'm about to spend some quality time this weekend checking all the sensors.

Any one with an idea which sensor/ resistor is responsible for turning on the fans when the AC is off. I believe TP mentioned theres a Low and High speed resistor?

Thanks!

Mark

[jerseyjoe]

Ok, I think I figured out what my temp gauge is going crazy. My radiator fan won't turn on when my AC is off. This causes my temp to go really high during stop and go traffic.

I'm about to spend some quality time this weekend checking all the sensors.

Any one with an idea which sensor/ resistor is responsible for turning on the fans when the AC is off. I believe TP mentioned theres a Low and High speed resistor?

Thanks!

Mark

<{POST_SNAPBACK}>

Well I just had this problem,sorta. My left fan would not turn on when the right did for cooling/low speed. It turned out to be the resistor under the fan motor. Was easy to replace since I had the bumper cover off for radiator cleaning.

If both of yours do not come on it may be a temp sensor. i would think both resistors would not go bad at the same time. IMO. hope this info is helpful.

[mark in sunnyvale]

Hi Joe,

Did you find out if there was a test spec for the resistor? Also, I would you happen to know the part number.

Of course, I just removed and re-install my front bumper over the weekend! Oh well, it wasn't that bad to remove it.

Thanks again!

[Loren]

I don't know the test spec - chances are you can't get a good reading without taking it out of the circuit. Porsche recommends (in the service manual) to cut the wire and then splice in the new one and cover with heat shrink tubing. You do not need to remove the bumper these are visible under the front fenders.

[mark in sunnyvale]

Thanks for the picture, Loren!

Joe, do you recall if your left fan turned on when you turned on the AC? I was looking at the description of operation for the fan. It said low speed should turn on if the AC is on. Then, I looked at the wiring diagram, I don't see how the resistor can be bypassed when AC is on. I'm starting to think my problem is not the resistor.

I might splice the resistor anyway, to check if I have an open circuit.

[Tool Pants]

Send me an email with the problem so I can print it out and show it to Peter, if you do not figure it out. I will be seeing Peter next week when he gets back from 987 school.

[jerseyjoe]

Thanks for the picture, Loren!

Joe, do you recall if your left fan turned on when you turned on the AC? I was looking at the description of operation for the fan. It said low speed should turn on if the AC is on. Then, I looked at the wiring diagram, I don't see how the resistor can be bypassed when AC is on. I'm starting to think my problem is not the resistor.

I might splice the resistor anyway, to check if I have an open circuit.

<{POST_SNAPBACK}>

PM me your number, i can explain it way better then i could write it all down

[Jenno]

When I had the resistor problem the fan would not come on with A/c or high temperature. The easiest way to access it is to loosen or remove the wheel-arch liner.

[mark in sunnyvale]

Thanks for the response everyone. I still haven't figured out what's causing my problem.

Jenno's post confirms that it's not a simple resistor problem. =(

I tested all the relay, and they all work fine. For anyone out there who needs to test their radiator fan relay, it's the same relay type as the horn. (position 10). I just swapped the relay from the fan to the horn and honked the horn (I'm sure my neighbors loved that). If it's broken, the horn will not work.

Back to my quest.

When I had the resistor problem the fan would not come on with A/c or high temperature.  The easiest way to access it is to loosen or remove the wheel-arch liner.

<{POST_SNAPBACK}>

[speed123]

Thanks for the response everyone. I still haven't figured out what's causing my problem.

Jenno's post confirms that it's not a simple resistor problem. =(

I tested all the relay, and they all work fine. For anyone out there who needs to test their radiator fan relay, it's the same relay type as the horn. (position 10). I just swapped the relay from the fan to the horn and honked the horn (I'm sure my neighbors loved that). If it's broken, the horn will not work.

Back to my quest.

When I had the resistor problem the fan would not come on with A/c or high temperature.  The easiest way to access it is to loosen or remove the wheel-arch liner.

<{POST_SNAPBACK}>

<{POST_SNAPBACK}>

TO ALL BOXSTER 2001 PRO OUT THERE, SIMPLE QUESTION ??

WHEN DO THE RADIATORS FANS COMES ON WHEN THE A/C IS SWITCHED OFF AND ENGINE IS RUNNING??

[Stefan]

Most resistors are coded with color stripes that tell you the intended resistance. Take a look at the existing ones to find out what they are supposed to be.

[PTEC]

Both side fans should come on low speed with AC operation. If you let the car idle long enough you should get high speed of both. If you're getting low speed but not high speed, then chances are the resistor is burnt out. If you're not getting either speed.... then I dunno.

If you didn't already check the fuses, each side has its own fuse.... C8 and C10 in the footwell fuse box.

Either way, I'm pretty sure the Fans are triggered by the DME whether the AC is on or not. The DME sees the AC operation over the CAN and then it triggers the fans.

[0586slb]

There are four relays in total. Two for the left fan, and two for the right. The first stage (or slow speed) relays - one for each side, are paralleled and will switch together, also the full speed relays are paralleled and will switch together too. They are switched directly from the DME, whether it decides the AC requires them or the engine is too hot.

Stefan, colour coded resistors are only used up to about 2W. (For printed circuit boards) Anything required to dissipate more power will not be colour coded.

PTEC, your description is slightly muddled, as the resistors being in circuit make the motors turn more slowly. Your description should have been "If you're getting high speed but not low speed, the resistors are burned out"

A very easy way to test the resistors without having to dive under the car, is to remove relay 19 & 20. Measure the resistance between pin 5 (87) of socket 19 and pin 5 (87) of socket 20. This should be 0.55ohm. Remove relay 21 & 22 and repeat. Again, 0.55ohm.

After all that, the temperature sensor is a split NTC device that has one sensor for the instrument cluster and one for the DME. One can go bad without the other, hooking the car up to a diagnostic computer will show this straight away.

Chris

[PTEC]

PTEC, your description is slightly muddled, as the resistors being in circuit make the motors turn more slowly. Your description should have been "If you're getting high speed but not low speed, the resistors are burned out"

A very easy way to test the resistors without having to dive under the car, is to remove relay 19 & 20. Measure the resistance between pin 5 (87) of socket 19 and pin 5 (87) of socket 20. This should be 0.55ohm. Remove relay 21 & 22 and repeat. Again, 0.55ohm.

After all that, the temperature sensor is a split NTC device that has one sensor for the instrument cluster and one for the DME. One can go bad without the other, hooking the car up to a diagnostic computer will show this straight away.

Chris

<{POST_SNAPBACK}>

This guy knows his stuff! I just looked at the wiring diagram, and you're exactly right about the high working but low not if the resistor was burnt out. Also about the double NTC coolant temp sensor being split between the DME and the cluster.

I learned something today.

[paolo356]

Thanks a lot guy, my left fan is off, now i can check relè and fuse,

i already changed the motor's fan, but without resolve the problem,

i think that this problem of high temperature cause the coolant tank failure, for high pressure, because now my tank leak and i must change it..... :(

Thanks Again from Italy

Paolo

Edited July 27, 2005 by paolo356