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Billy Mac 09-09-2002 06:00 PM

Both cooling fans stay on all the time
I have an 89 N/A 944 and both cooling fans are staying on all the time and they have run down the battery.My quess is cooling fan relay? What do ya'll think and where is located..Thanks for the help

thamlin000 09-09-2002 06:17 PM

I'm having fans problems myself, right now. Try this link. ns

Billy Mac 09-09-2002 06:28 PM

Great link Thanks

951carter 09-09-2002 10:32 PM

could also be the fan temp switch in the radiator

overkill 09-10-2002 01:57 AM

its probably the Thermo Switch.

Z-man 09-10-2002 08:30 AM

The cooling system on our cars are very, very complicated and can be expensive to fix. (ex: there's a separate circuit for the low fan speed vs. high fan speed). The fan switch relay is expensive ($125.00!).

If you're tracking down the problem on your own, like said before, start with the fan switches and thermo. Make sure that if you're going with a lower temp thermo, get the lower temp fan switches. (Not a bad idea at all, btw: gets your fans on sooner!)
If it is the fan switch, I'd replace both at the same time. (One of those if one goes, the other is likely to follow!)

Good luck!

Billy Mac 09-10-2002 03:40 PM

I bought the thermo switch today and then I came home and unplugged the connector from the old switch before I put the new one on to see if the fans would stop and Guess what one of the fans stayed on and the other turned off.The fan on the drivers side stayed on???? What next..Thanks Bill

divezic 09-11-2002 10:00 AM

I figured you had either a bad AC relay or a combined bad thermo switch and a bad cooling fan relay.

With your troubleshooting so-far I'll bet you had the latter. It looks like the cooling fan relay is still stuck in the closed (energized) position. Pull the relay and and use an ohm meter to see which pins are closed. De energized, it looks like pins 30 and 87 should have infinite resistance. Same with pins A and B. If either or both sets have close to zero resistance while deenergized, then the relay is bad.

Or lightly yet firmly tap on it a few times, reinstall, and see if that fixed it.

This is a swag because I'm looking at the schematics for an '84 944, but the wiring logic seems to be the same. I believe the relay is the same in early and late models (Part # 141-951-253B which is about $8 from Pelican Parts).

Makis 09-12-2002 03:26 PM


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.


Billy Mac 09-13-2002 05:35 PM

Does anyone have any idea where the fan relay is located.I'm going to work on my car Saturday...Thanks Bill

Bob's944 09-13-2002 05:42 PM

1 Attachment(s)
Not sure, but I think '89 is the same as 85.5... he's my list/ location diagram.... G-10

Billy Mac 09-14-2002 01:39 PM

Thanks for all the input, it was the fan relay and i got real lucky my next door neighbor used to own a used european car lot and he has a box full of old switches and relays and he had the one I needed. I must be livin right Thanks Bill

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