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Rear cooling fan

enzo

New member
Joined
23 Feb 2012
Messages
11
Hi Guys,
My rear cooling fan doesn't activate when I turn engine off..
Fan operates when engine is hot and I have ignition on but engine not running.
I've heard it cycle from slow to fast fan so just problem when I switch engine off.
Have checked fuse,relay and changed the resistor..
So issue seems to be power to fan only when ignition on
Any ideas guys??
 
enzo said:
Hi Guys,
My rear cooling fan doesn't activate when I turn engine off..
Fan operates when engine is hot and I have ignition on but engine not running.
I've heard it cycle from slow to fast fan so just problem when I switch engine off.
Have checked fuse,relay and changed the resistor..
So issue seems to be power to fan only when ignition on
Any ideas guys??

Hi,

The rear cooling fan will only operate when the engine is turned off if the engine temp is above a certain temperature. I'm sorry but I cant remember what that temperature is, however I'm sure Tore B will be along shortly and give you that information.

Here in Spain after a brisk drive my fan cuts in after about 5 minutes of leaving the car in the drive. Runs for about a minute then cuts out, 5 minutes later it cuts in again and then out, does this 2 or 3 times.

Always makes me think that if someone was walking by when it kicked in it would frighten the s**t out if them as there would be no one in the car.

ATB :)

Here you go, just got this off Tore B's web site. Quote"


Rear (AUX) fan
The rear fan(s) has two purposes. (Turbo models have two rear fans) One is to help blowing air through the heat exchangers onward to the front fans to improve the heating of the cabin. The fan run at two speeds, and typically starts at mid temperature setting on the CCU. The fan will run on low speed if the fan speed knob on the CCU is below 2. Fan settings above 2 will set the rear fan speed to high. Remember, the operation of the fan is also dependent on the temperature setting, i.e. if it's set to minimum, the rear fan will not start since no heated air is needed to the cabin. However, on minimum temp setting, the fan could automatically be started by the cooling function, see below.
The second function of the rear fan is to do additional cooling of the heat exchangers/engine when in normal operation, (if temperature knob is set to minimum and mixer servo flaps are closed) and at ignition off by blowing the heated air out through two spring loaded dump valves under the engine. The mixer flaps closes to enable the fan to build up enough air pressure to open the dump valves.
The CCU supervises the engine/air duct temperature with a temperature sensor, (see picture) and run the fan at low speed (40-45degC) and high(62-57degC) when ignition is ON and mixer valves are closed. (minimum heat setting) At igntion OFF, the fan run in low speed if the air duct temperature is above 75degC, and shall stop when below 70degC. The maximum fan run time at ignition off is 20 minutes. If the fan does not stop you might have a problem with the temperature sensor or the fan relay.
Un Quote"
 
Thanks for the replies
Sorry my post was not so clear..
The rear fan functions as normal except for the cooling cycle .
When engine is cold and I switch ignition so dash lights illuminate..the fan does not operate (normal) but after driving and engine off and hot .. If I turn ignition so dash lights operate I can hear the fan operate to cool engine down ..
The problem is when I remove the key the fan doesn't operate even though engine is hot
So wondering is there a relay or switch that powers the fan independently of the ignition..
Thanks
 
The rear fan is controlled by the Climate Control Module, and it uses a temperature sensor mounted in the rear air duct to control the operation at ignition off. This temp sensor is NOT the cylinder head temp sensor.

You might have a problem with the air temp sensor, you could measure it with an Ohmmeter or use an OBD tool to read out the read value in the CCU.

My DIY page has the information already quoted in the post above, as well as pictures of where the sensor is placed, see the Details page:
www.porschehvac.bergvill.com
Cheers,
Tore
 
Thanks Tore
Will get CCU read..
One final question should the fan operate with temp 9 o'clock on gauge when I turn engine off, and does it start straight away or as mentioned before 5 mins after engine off..
 
It does not matter what temperature setting you have on the CCU, at ignition off the rear fan will start if it's hot enough back there, and it can be active for up to 20 minutes. I've never seen it starting up after five minutes with ignition off though, but it is possible it can do so.
Cheers,
Tore
 
ToreB said:
It does not matter what temperature setting you have on the CCU, at ignition off the rear fan will start if it's hot enough back there, and it can be active for up to 20 minutes. I've never seen it starting up after five minutes with ignition off though, but it is possible it can do so.
Cheers,
Tore

Hi ToreB,

Yep it probably is more than 5 minutes, I seem to get in, unpack the shopping :D and then hear it through the kitchen window, maybe more like 10 to 15 minutes after stopping and then active for the 20 odd minutes you mention, cutting in and out.

ATB :)
 

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