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I have a 2000 Boxster S, and after completing the heater box foam repair and properly purging cooling system I noticed that my radiator fans did not come on when operating temp was reached, but they do work when AC is in operation. Any clues for determining fault would be appreciated.

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I have a 2000 Boxster S, and after completing the heater box foam repair and properly purging cooling system I noticed that my radiator fans did not come on when operating temp was reached, but they do work when AC is in operation. Any clues for determining fault would be appreciated.

Frank:

Is it possible that It may have been that way before you repaired the heater box foam, but may not have been aware of it?

The fans and the two speeds are controlled by four relays (two for each fan, with each of the two sets having a low speed and a high speed) and two ballast resistors (one on each side).

Since the fans are working (even though it's only on the high speed), it's not the fan motors and not the fuses. If you want to double check the fuses, they are C8 (radiator fan right) and C10 (radiator fan left). Both are 40 amp fuses.

The ballast resistors' ceramic coating frequently crack because they get hot and are then sometimes splashed by cold water (as when you go over a puddle).

The relay tray is located on the left kick panel, to the left of, and below the level of your left knee as you sit in the driver's seat.

Here is a photo showing the location of the relays and the fuses (click on it for a good look):

post-6627-0-16716200-1300293863_thumb.jp

For reference to locate the relay tray, you can just see the top of the dead pedal in the bottom right corner. The four relays are in the lowest visible position when the fuse panel cover is still on (there is another row of relay receptacles below the visible row, but no relays installed in that row). The left low speed is position 19 in the relay tray, the right low speed is position 21 in the relay tray.

Fuse Row C is two rows below row A, and position "10" is closest to the side shown by the fuse arrow.

To test whether your resistors are bad (and thus not causing the fans to go on low speed), with the engine running and the engine temp below 206 degrees (e.g., engine cold), put your finger on relay 19 and then press the snowflake button on and off to turn on your a/c on and off. You should be able to feel (and hear) the relay clicking. Repeat with relay 21.

If the relay clicks and the low speed fan does not go on, then your resistor is the most likely culprit. If the relay does not click, then the relay itself may be faulty, or there is a problem with the wiring or fuse. Again, if the high speed fan is running, it's not the fuse.

The resistor is part number 996.616.101.00 although there may be a TSB with an updated part number for a new design resistor pack.

Here is a photo of what the resistor looks like on the right side and its location behind the fan housing, near the frame rail:

post-6627-0-85729400-1300295289_thumb.jp

Note that you will have to remove the front of the wheel well liner to access it for viewing and replacement.

Keep us posted with what you find.

Regards, Maurice.

Edited by 1schoir
  • Upvote 2
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I have a 2000 Boxster S, and after completing the heater box foam repair and properly purging cooling system I noticed that my radiator fans did not come on when operating temp was reached, but they do work when AC is in operation. Any clues for determining fault would be appreciated.

Frank:

Is it possible that It may have been that way before you repaired the heater box foam, but may not have been aware of it?

The fans and the two speeds are controlled by four relays (two for each fan, with each of the two sets having a low speed and a high speed) and two ballast resistors (one on each side).

Since the fans are working (even though it's only on the high speed), it's not the fan motors and not the fuses. If you want to double check the fuses, they are C8 (radiator fan right) and C10 (radiator fan left). Both are 40 amp fuses.

The ballast resistors' ceramic coating frequently crack because they get hot and are then sometimes splashed by cold water (as when you go over a puddle).

The relay tray is located on the left kick panel, to the left of, and below the level of your left knee as you sit in the driver's seat.

Here is a photo showing the location of the relays and the fuses (click on it for a good look):

post-6627-0-16716200-1300293863_thumb.jp

For reference to locate the relay tray, you can just see the top of the dead pedal in the bottom right corner. The four relays are in the lowest visible position when the fuse panel cover is still on (there is another row of relay receptacles below the visible row, but no relays installed in that row). The left low speed is position 19 in the relay tray, the right low speed is position 21 in the relay tray.

Fuse Row C is two rows below row A, and position "10" is closest to the side shown by the fuse arrow.

To test whether your resistors are bad (and thus not causing the fans to go on low speed), with the engine running and the engine temp below 206 degrees (e.g., engine cold), put your finger on relay 19 and then press the snowflake button on and off to turn on your a/c on and off. You should be able to feel (and hear) the relay clicking. Repeat with relay 21.

If the relay clicks and the low speed fan does not go on, then your resistor is the most likely culprit. If the relay does not click, then the relay itself may be faulty, or there is a problem with the wiring or fuse. Again, if the high speed fan is running, it's not the fuse.

The resistor is part number 996.616.101.00 although there may be a TSB with an updated part number for a new design resistor pack.

Here is a photo of what the resistor looks like on the right side and its location behind the fan housing, near the frame rail:

post-6627-0-85729400-1300295289_thumb.jp

Note that you will have to remove the front of the wheel well liner to access it for viewing and replacement.

Keep us posted with what you find.

Regards, Maurice.

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I have checked fuses and pulled relays and jumped each one of them. when jumped the fans operate and when AC is engaged the fans operate. I just let the car run for half hour and the fans did not come on. I reached into radiator ducts and radiators did not seem warm. Could a faulty thermostat be the problem? My temp reads rite on the O of 180, and by the way I am in Houston so cold ambient temp should not be an issue.

Thanks

Frank

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I have checked fuses and pulled relays and jumped each one of them. when jumped the fans operate and when AC is engaged the fans operate. I just let the car run for half hour and the fans did not come on. I reached into radiator ducts and radiators did not seem warm. Could a faulty thermostat be the problem? My temp reads rite on the O of 180, and by the way I am in Houston so cold ambient temp should not be an issue.

Thanks

Frank

Frank:

When you say that when the A/C is engaged the fans operate, are they operating on the low speed?

The thermostat and its effect on the water temperature will not interfere with the clicking relay test when you depress the A/C switch. If the low speed fans do not turn on, the resistor is suspect.

Keep in mind that the fans are not supposed to turn on at all when the water temperature is below 206 degrees or the A/C is not turned on. The high speed only kicks in when the water temperature reaches over 215 degrees or the A/C freon pressure goes over a certain level.

If the fans are operating at the low speed when you turn on the A/C, even when the engine is below 206 degrees, they are working properly.

Regards, Maurice.

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I have checked fuses and pulled relays and jumped each one of them. when jumped the fans operate and when AC is engaged the fans operate. I just let the car run for half hour and the fans did not come on. I reached into radiator ducts and radiators did not seem warm. Could a faulty thermostat be the problem? My temp reads rite on the O of 180, and by the way I am in Houston so cold ambient temp should not be an issue.

Thanks

Frank

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  • 4 months later...

Anyway both fans are suposed to turn on?

On my 996 when I turn on the AC only the right fan turn on, how i can jump the resistor of the left fan to see if it is working or not? I also checked the relays, it seems that they are all ok...

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I don't know how to jump the resistor but you can turn them on in high or low with the Durametric software. Otherwise I guess you could see if both fans work in high speed when the coolant gets really hot. If both fans run in high but only one in low I guess it would be the resistor. If one fan never runs and the other runs in both high and low may be you've got a bad fan or bad connection to the fan. I think the resistor is out of the picture in high speed.

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  • 7 months later...

Appears my passenger side resistor is faulty. Used Durametric to activate the fans (didn't have an option for low/high, as some posts suggested) and only the driver's side came on. Swapped both low speed fan relays and the problem didn't follow the relay. When the car got hot enough, both high speed fans came on. So definitely got to be the passenger side resistor.

Thanks for the info and pics in this thread! They all helped for me to make this determination.

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  • 1 month later...
  • 9 months later...

2001 911 C2, body 996

After reading several threads about this subject and testing my car I found that.. The original problem was the 40A fuse, C8, for the passenger side fan was blown. After replacing the fuse both fans started to work when the A/C compressor was switched on or after reaching a temperature of 206?? (little over half way on water temp meter). But it appeared that only one speed of fan operation was working. After further testing I found that by jumpering each of the 4 relays on at a time I could cause each fan to come on, low speed and high speed, one at a time, all worked. So there was no problem with the ballast resistors. What I did find was that when the water temp was low, and the A/C was switched on, the fans came on in low speed, not high speed (as is stated several places in threads) and that my temperature never got high enough for high speed fans to come on. Only the low speed fan is used, unless the water temp gets very high??. Ambient temp was about 76deg F

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Of course, there is the lingering question of what caused the C8 fuse to blow in the first place. Fuses aren't supposed to blow unless excess amps go through them. And they are supposed to be sized so that normal operation doesn't blow them. So something abnormal lurks.

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If the A/C is on, the fans should operate at low speed regardless of coolant temperature. If one or both fans don't operate at low speed with the A/C on, then the non-working fan's ballast resistor is likely broken.

In my case, both ballast resistors were broken. Before I replaced them, the fans would operate at high speed when the A/C was on the the refrigerant pressure reached a trigger point. Then the expansion value would equalize the high and low pressure sides and the 'high speed' fans would turn off. After replacing both resistors, the fans began low speed operations as soon as I turned on the A/C.

Summary: ballast resistors are OK, the fans operate at low speed when the A/C is turned on. One or more ballest resistors broken, one or both fans run at high wpped with the A/C on after refrigerant reaches a trigger pressure level and they stop running when the expansion valve equalizes the pressure. Of course, a high collant temperature can keep the fans running at high speed in effect overiding the A/C signals.

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