One fan not working?
04-15-2011, 09:54 AM
#16
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I like it when people use the search function and pull up the old thread. It keeps all of the distilled goodness in one place.
04-15-2011, 10:54 AM
#19
08-17-2013, 12:53 PM
#20
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996 AC cooling fan
During a once over inspection the mechanic IDd that the right AC cooling fan did not operate at low speed. Although obviously not ideal does this need to be addressed? They recommended the right side cooling fan be replaced at a cost of $983. what do you think? Thanks
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.
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.
08-17-2013, 01:54 PM
#21
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did you read the post that you quoted? If it runs at high speed but not at low speed it is probably the ballast resistor. ~$80.
"...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...."
Also post #5:
"...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..."
"...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...."
Also post #5:
"...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..."
08-17-2013, 03:30 PM
#22
Rennlist Member
Thanks, very informative. My fans are working fine, but I always appreciate this kind of tech post.
On air cooled 911's, it was a pretty common mod to wire the oil cooler fan to a switch in parallel for increased cooling. I wonder if a 'put my radiator fans on high' override switch would be helpful on the 996, particularly for track days? It would be simple enough to wire and would force the fans to run even if the coolant is below 215F
Here's the original post from the old Porsche Pete's Boxster Board thread linked to above. Note that is was all written for a Boxster, not a 996...
On air cooled 911's, it was a pretty common mod to wire the oil cooler fan to a switch in parallel for increased cooling. I wonder if a 'put my radiator fans on high' override switch would be helpful on the 996, particularly for track days? It would be simple enough to wire and would force the fans to run even if the coolant is below 215F
Here's the original post from the old Porsche Pete's Boxster Board thread linked to above. Note that is was all written for a Boxster, not a 996...
Originally Posted by Boxsterra on the old PPBB
Just before I left for BRBS I discovered that my passenger-side radiator fan wasn't working on the low speed. Knowing that I was going to be doing some hard driving in warm weather, I devised a hack to remediate the problem at least until I could fix it properly. The hack worked well, keeping the temps in check, even in sustained high-revving runs in hot weather.
At BRBS I did the same hack on two other cars with similar success. It seems to be a common problem that many of the older cars have at least one non-operational low-speed radiator fan.
Description
The radiator fans in the Boxster run at two speeds. The low speed runs when the car engine temp is higher than 206°F or the A/C is on. The high speed runs when the coolant temperature is higher than 215°F or the A/C freon pressure is higher than 16 bar. The low speed is controlled by a ballast resistor which is prone to eventual failure.
Diagnosis
With engine coolant temperature under 206°F, turn on your car and the A/C. Put your hand under the front bumper in front of each of the front wheels and feel for moving air from the fan. If there is no moving air then likely one of the ballast resistors is no longer working.
To determine that the problem is the resistor and not some other part of the system, get in the car, start the engine, and put your finger on the appropriate low-speed fan resistor (see below for diagram). Press the A/C (snowflake) button on then off. You should be able to feel the relay click. If not the problem is the fuse, the relay, or the wiring.
You also need to verify that the problem isn't the fan itself. Leave the car running with the A/C on and wait until the temperature reaches 206°F. The fans will kick into high speed and at this point, chances are both fans will be running. If not, there is a problem with the actual fan, the fuse, the relay, or the wiring.
Hack
There are four relays that control the radiator cooling fans: left low speed, left high speed, right low speed, and right high speed. This is also the order that they are found on the relay panel. They are relays 19, 20, 21, and 22 in this diagram:
The relay panel is under the left side of the driver's side dash. The bottom of the relay panel is about the same level as the OBD2 plug so you really have to get your head under there to see it. In this picture you can see the clutch pedal and dead pedal for reference. Note that it is not necessary to remove the fuse holder cover as shown in this picture (this pic is actually from a different hack).
Remove both the low-speed and high-speed relays for the fan that isn't working. Cut and strip a piece of wire about 1.5" long.
Insert one bare end in the output socket (pin 87, center bottom horizontal slot) for the low speed relay and the other end in the output socket for the high speed relay.
Put the relays back and test the hack. Start the car (coolant temp less than 206°F), turn on the A/C and verify that both fans are now operating.
Fix
The proper fix is to replace the ballast resistor. I will cover that procedure in a different post.
At BRBS I did the same hack on two other cars with similar success. It seems to be a common problem that many of the older cars have at least one non-operational low-speed radiator fan.
Description
The radiator fans in the Boxster run at two speeds. The low speed runs when the car engine temp is higher than 206°F or the A/C is on. The high speed runs when the coolant temperature is higher than 215°F or the A/C freon pressure is higher than 16 bar. The low speed is controlled by a ballast resistor which is prone to eventual failure.
Diagnosis
With engine coolant temperature under 206°F, turn on your car and the A/C. Put your hand under the front bumper in front of each of the front wheels and feel for moving air from the fan. If there is no moving air then likely one of the ballast resistors is no longer working.
To determine that the problem is the resistor and not some other part of the system, get in the car, start the engine, and put your finger on the appropriate low-speed fan resistor (see below for diagram). Press the A/C (snowflake) button on then off. You should be able to feel the relay click. If not the problem is the fuse, the relay, or the wiring.
You also need to verify that the problem isn't the fan itself. Leave the car running with the A/C on and wait until the temperature reaches 206°F. The fans will kick into high speed and at this point, chances are both fans will be running. If not, there is a problem with the actual fan, the fuse, the relay, or the wiring.
Hack
There are four relays that control the radiator cooling fans: left low speed, left high speed, right low speed, and right high speed. This is also the order that they are found on the relay panel. They are relays 19, 20, 21, and 22 in this diagram:
The relay panel is under the left side of the driver's side dash. The bottom of the relay panel is about the same level as the OBD2 plug so you really have to get your head under there to see it. In this picture you can see the clutch pedal and dead pedal for reference. Note that it is not necessary to remove the fuse holder cover as shown in this picture (this pic is actually from a different hack).
Remove both the low-speed and high-speed relays for the fan that isn't working. Cut and strip a piece of wire about 1.5" long.
Insert one bare end in the output socket (pin 87, center bottom horizontal slot) for the low speed relay and the other end in the output socket for the high speed relay.
Put the relays back and test the hack. Start the car (coolant temp less than 206°F), turn on the A/C and verify that both fans are now operating.
Fix
The proper fix is to replace the ballast resistor. I will cover that procedure in a different post.
07-28-2016, 05:26 PM
#24
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Fan help
I just wanted to help some of you guys with fan issues . I read that there is a hack to bypass the fan resistor by jumpering relays, I tried this and it didn't work for me. I did however cut out the resistor and solder the 3 wires together because my fan was not working ( trying jumpers on relays and everything ) . I was worried that the wires might get hot bypassing the resistor but they did not even get warm. I now have a fan that comes on with the Ac button on and when the car reaches the correct temp to kick it on. I will tell you it now only comes on high speed but being in Texas that's a good thing. I'm posting this because I could not find anything about just removing the resistor , it works great but it's always straight to high speed. If you dont mind the extra noise and a cooler temp in traffic ( or its just a hot area) . It's better for you Ac system also as it reduces the pressure. I am figuring out a lot about these cars because I had to install a ls3 engine into her after the failed engine bearing and now have better cooling for a 530hp v8.... Don't hate me !!!
2002 c4s with a lope is pretty cool.
Also yes the regular 996 is a different fan and radiator that the c4s and turbo but they both work by bypassing the resistor..
2002 c4s with a lope is pretty cool.
Also yes the regular 996 is a different fan and radiator that the c4s and turbo but they both work by bypassing the resistor..
07-28-2016, 05:34 PM
#25
Rennlist Member
I just wanted to help some of you guys with fan issues . I read that there is a hack to bypass the fan resistor by jumpering relays, I tried this and it didn't work for me. I did however cut out the resistor and solder the 3 wires together because my fan was not working ( trying jumpers on relays and everything ) . I was worried that the wires might get hot bypassing the resistor but they did not even get warm. I now have a fan that comes on with the Ac button on and when the car reaches the correct temp to kick it on. I will tell you it now only comes on high speed but being in Texas that's a good thing. I'm posting this because I could not find anything about just removing the resistor , it works great but it's always straight to high speed. If you dont mind the extra noise and a cooler temp in traffic ( or its just a hot area) . It's better for you Ac system also as it reduces the pressure. I am figuring out a lot about these cars because I had to install a ls3 engine into her after the failed engine bearing and now have better cooling for a 530hp v8.... Don't hate me !!!
2002 c4s with a lope is pretty cool.
Also yes the regular 996 is a different fan and radiator that the c4s and turbo but they both work by bypassing the resistor..
2002 c4s with a lope is pretty cool.
Also yes the regular 996 is a different fan and radiator that the c4s and turbo but they both work by bypassing the resistor..
