I am trying to find a well defined fan functioning guide, i.e., with the key on and the engine off, what is running, and if the engine is off and the key on and then switch the a/c on without engine running, does anything run.... then once engine is running, does anything run, or nothing until the thermostat tells fan one to run, and if engine is not hot enough to run fan one, but i trun on ac with engine running, does fan two only come on and or both fan, regardless of whats hot ot whats not.

this may all be mapped out somewhere here but i did some searches , and none of it seems too well defined, and to what when and why with our fans.

I am repairing my 944 and havent had it on the road drving it yet, and want to catch these things before i even attempt to do so.

Thank you to all who respond. <img src="confused.gif" border="0">

 

An FAQ from "notJustPorsche" e-group.
Courtesy fo Makis Livadis

Hope this helps
-----------------

Hi,

A number of people have complained in the past that their porkers
radiator fans are on all the time. This happened to me today again. I
decided to get the books out and study this phenomenon and try to
undestand it once and for all.

Principle of operation of the Fans
The 944 post 85/2 is equiped with two Fans. The Fans are controlled
by a control unit that is capable to drive the fans at two speeds.

The control unit takes input from the following sources.
1. Two termo-switches monitoring the coolant temperature, one is
activated at 92C and the other one at 102C.
2. One AC Low Pressure or refrigerand temperature switch.
3. AC switch.
4. One Intake pipe cooling switch (16V models).


From the wiring diagram I can deduce the following action.
1. Thermo-Switch (92C) on - Forces low speed fan operation. Note,
both fans are on not just one.
2. Thermo-Switch (102C) on - Forces high speed fans operation.
3. AC Low Pressure switch on - Forces high speed fans operation.
4. AC switch on - Causes high speed fans operation (probably)
5. One Intake pipe cooling switch (16V models)on at 42C - same as AC
switch on.

Control Unit pinout
30M1 - 12V Fan1 power
30M2 - 12V Fan2 power
V1 - Slow Fan1 speed
V2 - Slow Fan2 Speed
M1 - Fast Fan1 Speed
M2 - Fast Fan1 Speed
TS - 92C Thermal Switch grounded on switch on
TF - 102C Thermal Switch grounded on switch on, also AC low pressure
switch grounded on switch on.
X - 12V Control unit power.
31 - Ground
AC - 12V if either AC switch or Intake pipe cooling switch (16V
models) is on.

Debugging procedure
I believe the fans should be on if TS or TF are grounded and AC is
set to 12V. So if the fans are on after switching engine off and
ignition on to the following:
1. Remove cotrol unit
2. TS grounded? If yes, low speed fans selected.
3. TF grounded? If yes, high speed fans selected. (note this
overwrites 2 above)
4. AC at 12? If yes, high speed fans selected.
5. If none of 2,3, 4 Fans should be stoped.
6. If 5 but fans running then control unit likely to be broken.

Hope this info helps if you are affected by this phenomenon.

I think in a hot summer day if the fans are running more than you
would expect blame porsche. But they may have a reason for doing so.
If on a cold winter day this is still the case then suspect something
wrong with your car.

Makis

 

test sorry ignore

 

Im really surprised that no one has come up with a flow chart or something to spell out in simple terms the fan issues, relating to my former question.

still looking for answers. <img src="confused.gif" border="0">

 

nobody at all eh?