924turbo2

I searched a lot on the forum but can't find a solution. As soon as I turn my key, thet oil cooler fan and ac condensor fan starts running at full speed.. Wiring loom looks good and oil sensor is connected.

I have another 964 from 89' so I switched the relay R04 en R14, problem stay's the same.

The CCU form the 964, I have put in the other 964 and if I turn the key the fans starts spinning. I did notice the other 964 had a CCU with a 993 partnumber and the modification in the wiring loom (Workshop Manual S.87-27). So this my mislead.

What can I test next ?

Rocket Rob

The fans are both controlled by the CCU. I would start using ToreB's diagnostics page. Good luck and keep us posted.

https://www.bergvillfx.com/porschehvac1

Kappi2907

Check link below, loads of info on cooler system problems:

https://www.pelicanparts.com/techart...ubleshoot2.htm

Navaros911

Souns like the ceramic encased resistors that sit on top of the coolers are possibly shot.

The car goes into max cooling mode immediately upon key turn when a fault is detected.

Search for it here, lots of info. The right side one is a pain to get to.

Picture of my car with no front bumper or wing for reference.

ToreB

The CCU must have a 964 part number in order to work correctly in a 964. A 993 unit could be made to work with wiring modifications.
Using a 964 unit in a 993 or a 964 with wiring modifications will cause malfunction of the unit, and even damage the unit.

I would start with reading out any OBD fault codes from the unit to determine the cause for these problems. This could be faulty sensor signals causing the unit to turn on the fans, or faulty CCU fan relay outputs.
Cheers,
Tore

AKB991

This may have nothing to do with the issue at hand... my 91 C4's AC fan is always running. So long as the key is in the ignition - the fan runs. I can control the speed w/ the appropriate **** but it's always going.
I did not think this made any sense and when I brought it in for servicing , to a well known / respected, indy P shop, they told me nothing is wrong. Apparently, SOME of the 964's have the fan running all the time while others
do not? I cannot claim to anything more than what I was told about it. I've always wondered if this is truly the case or not. Sorry to side track if this is irrelevant. Tore, you rock, thank you for all you do for us.

Spyerx

There are multiple fans:

the dash/suitcase fans
the front radiator ac and oil cooler fans

The ac radiator fan will only turn on when the ac is running

The oil fan only when oil is 'hot'

If the oil cooler and ac fans are always running, as Tore said, likely a CCU issue. I think a resistor issue would only manifest itself as running on high when running


The interior fans will either always run or only run on 1+, depending on year. I have a 91 and they are always on low.

AKB991

Spyrex, thanks for your response and valuable info.
Good to know that my interior fans are on all the time and that’s the way it should be. I do get some white “flakes” from the unit it times. Looks like a tiny snow storm but that’s another thread. Mine too is a 91 (C4).

924turbo2

Thank you for all the info, I tested a few thing today ,

Just to be clear what the problem is, as soon as I turn on the igniton (car/ oil fully cold), both oil cooler fan and ac condensor fan in front will turn on at high speed.

- jump the relay oil cooler and condensor fan, both low and high speed work
- restistance check of the oil cooler sensor, same as my other 964
- resistance at the CCU plug of the oil cooler sensor, same as the measured direct on the oil cooler sensor.
- Opened the CCU, look all good, nog bad solder jounts
- plugged of the two connecters of the CCU and the fans both stop turning.
- relay's R04 and R14 both work fine

Only thing I doubt is the wires of the oil temperature sensor measures around 4/5 volt between them, is this correct ?

ToreB

What part number is this CCU?

The best way to check the oil temperature sensor is to disconnect the CCU and measure on the CCU harness connector:
Ohmmeter, connect GND lead to pin G18, plus lead to pin G12. Reading shall be 22.6kOhm at 20°C, 3.8kOhm at 60°C.
The CCU puts a positive voltage on the sensor, so your measurement is normal.

It may well be that the internal CCU relay outputs for these two fans are defective. This can be fixed.
Cheers
Tore

kkswow12

sub'd here, i have a '90 and heater fan(i think) is on as soon as the key is inserted...kinda a background thing but i will get to it eventually, this could be a help...thanks...

924turbo2

Thanks Toreb, the partnumber is not visible anymore, but there are no wire modifications on the plug like my other 964 with the 993 part. CCU. I tested the (defect?) ccu in my other 964 and the fans start spinning, so the same problem.

The oil temperature sensor has the correct resistance.

I will check the relay in the ccu, anything else I can check ?

ToreB

You can read out the part number by using a Porsche compatible diagnostic tool. This would also be handy to read out all fault codes. If the CCU has two A/C switches, it is a 993 unit.
The CCU relay drivers are integrated circuits, not relays. You need CCU schematics and electronics knowledge in order to understand the internals.
Cheers,
Tore

MarcusG

What did we do before the internet?

Thanks Tor

Spyerx

I have the tools Torre mentions for any 964 owners in SoCal... happy to help get more of these running right! :-) PM me offline.