Radiator fans, interesting find
07-12-2002, 04:58 AM
#1
Racer
Thread Starter
Radiator fans, interesting find
The day before yesterday I turn the key to the ignition on position (without starting the motor) and both fans start to run at full tilt with a completely cold engine (a/c button off, all controls to far left). It had done this once before but I thought I had it fixed. Somthing else to note is the car has always run on the hotter side of warm. I am giving this problem top priority.
I have not completed the troubleshooting steps that are detailed in the shop manual yet, but I thought I would post what I found while evaluating the fan system.
I don’t know what Year the 928 incorporated the infinitely variable fans with flap control, but these units are quite complicated. One of the sensors that contributes input to the system is the gold anodized two poll CAN that sits on top of the A/C drier known as the Pressure Sender, Frigen (Porsche shop manual) or the Pressure Transmitter P/N 928.606.150.00 (PET5). This is by no means a simple on and off switch. It is a Frigen sophisticated little unit with many moving parts and a miniature rheostat inside of it.
For starters when removing or installing either of the nuts that hold the two harness wires in place, be very careful not to apply too much force in either direction. Those bolts are hollow. A wire runs up the middle of each bolt and are soldered to the tip. The red wire is connected directly to the rheostat and the blue wire is connected to a hinged plate with two spring-loaded arms that are moved by A/C PSI up and down the rheostat.
So the next time you open the hood to check your oil, peel back the two rubber boots to see if anyone has broke off one of the hollow bolts and simply reattached the harness wire with the remaining threads (minus the red or blue wire now). It worth a look!
Cheers
Max
I have not completed the troubleshooting steps that are detailed in the shop manual yet, but I thought I would post what I found while evaluating the fan system.
I don’t know what Year the 928 incorporated the infinitely variable fans with flap control, but these units are quite complicated. One of the sensors that contributes input to the system is the gold anodized two poll CAN that sits on top of the A/C drier known as the Pressure Sender, Frigen (Porsche shop manual) or the Pressure Transmitter P/N 928.606.150.00 (PET5). This is by no means a simple on and off switch. It is a Frigen sophisticated little unit with many moving parts and a miniature rheostat inside of it.
For starters when removing or installing either of the nuts that hold the two harness wires in place, be very careful not to apply too much force in either direction. Those bolts are hollow. A wire runs up the middle of each bolt and are soldered to the tip. The red wire is connected directly to the rheostat and the blue wire is connected to a hinged plate with two spring-loaded arms that are moved by A/C PSI up and down the rheostat.
So the next time you open the hood to check your oil, peel back the two rubber boots to see if anyone has broke off one of the hollow bolts and simply reattached the harness wire with the remaining threads (minus the red or blue wire now). It worth a look!
Cheers
Max
07-12-2002, 10:57 AM
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Interesting reading Max - thanks for sharing.
FWIW - I believe that the S4 models are the beginning of the flaps/fans mods for the engine cooling.
Actually, the fans are only 3 speeds (voltage signals sent from the controller based on inputs from coolant temperature, AC pressure, and transmission temperature) and the flaps are 2 positions as well (30% and full open based on the same input parameters).
FWIW - I believe that the S4 models are the beginning of the flaps/fans mods for the engine cooling.
Actually, the fans are only 3 speeds (voltage signals sent from the controller based on inputs from coolant temperature, AC pressure, and transmission temperature) and the flaps are 2 positions as well (30% and full open based on the same input parameters).