MeloB

In Feb of this year I got my first Porsche, a new to me '95 Canadian 993 with 66k miles. Very happy so far but I noticed that the rear blower fan stays on for 20 mins after the engine is shut off. I have read multiple threads on this, or related topics, without being able to understand whether this is normal or if the fan is indeed running too long. So I ran a Durametric diagnostics and the following codes came up, in order:

15 - Rear blower temp sensor
24 - Fresh air flap motor
32 - Right mixing flap motor
43 - Rear blower motor - Stage 1
44 - Rear blower motor - Stage 2
45 - Inside sensor motor
46 - Rear blower motor - Stage 1
47 - Rear blower motor - Stage 2

Starting with the easiest, I changed:

1) Series Resistor for Engine Compartment Blower Motor (in Blower Duct)
Part #: 964-616-550-02-M100

2) Temperature Sensor (in Blower Duct) for Engine Compartment Blower Motor
Part #: 964-659-120-00-M100

Have noticed no change at all in fan behavior. Fan turns on as soon as ignition key is in "On" position and after the engine is turned off, regardless of how long it has run, it will run for 20 mins then shut off.

Is this normal? Do I need to look into something else? One of the concerns is obviously battery life...

Appreciate the help.

Thanks,
Mel

ToreB

These fault codes are commonly seen, the rear fan has obviously been malfunctioning some time in the past. The rear fan shall run in cooling mode if the temperature is high enough in the rear duct, and runs as long as the CCU is on after ignition off, up to 20 minutes.
What is the rear temperature when this happens? You could use the OBD tool to read out the sensor reading.
Does the fan run in low and high speed when testing it like this:
-Cool engine and rear temp sensor
-Set CCU temp and fan to minimum. rear fan should not run
-Set temp to max, rear fan shall run in low speed
-Set fan speed to 2 or above, rear fan shall run on high speed

Cheers,
Tore

MeloB

Thanks for the quick response Tore. Please see below for some answers to your questions. Sorry if these don't make sense...

What is the rear temperature when this happens? - I wouldn't call it hot. Ran the engine for no more than 4-5 minutes, fan stood on for 20 minutes. Even when I turn the ignition key to On with car completely cold, after sitting for days, fan will go on until removing the key.You could use the OBD tool to read out the sensor reading. - I will try and run it tomorrow, don't have it at the moment
Does the fan run in low and high speed when testing it like this - Is the procedure below run with the engine Off or On? Key in On position?
-Cool engine and rear temp sensor
-Set CCU temp and fan to minimum. rear fan should not run
-Set temp to max, rear fan shall run in low speed
-Set fan speed to 2 or above, rear fan shall run on high speed

ToreB

The test procedure is done with ignition on and engine not running.
Cheers,
Tore

MeloB

Here we go:

Ignition On, Temp and Fan at Min - Fan on
Temp at Max - Fan On
Fan at 3 - Fan on High speed

MeloB

Can anyone make sense of this? Appreciate the help,

Mel

ToreB

It looks like the CCU relay output is shot. This can be repaired.
Cheers,
Tore

MeloB

Thanks Tore!

Is there a part number for it? Can't seem to locate a "CCU Relay"...

Mel

Dryfly57

Hope the relay is not internal. Tore will lead you in the right direction.

ToreB

Sorry for the confusion.
The CCU has several semiconductor outputs to operate the various relays in the car. These IC's can fail, sometimes in a conducting state, causing a relay to be activated all the time when the CCU is on.

The above indicate that there is something wrong with the rear fan CCU relay outputs. However, the most common causes for HVAC problems in the 964 and 993 is not inside the CCU.

Cheers,
Tore

MeloB

Tore, thank you for the clarification. Where do you suggest I start? Is it worth pulling the CCU unit out or should I start somewhere where these problems occur more frequently?

Regards,
Mel

pp000830

What is the functional (heating cooling experience) implication of the fan running because of a failed semiconductor output?

MeloB

For me it's more about the battery drainage than the functional experience. The AC blows cold so I haven't noticed anything in that regard.

I worry that the heavy load from the aux fan running is draining the battery. I just had to replace the old one (less than 3 yrs old, bought by previous owner) and using a trickle charger now...

Mel

07C4S

My A/C stopped working Monday. I went thru the Bergvill diagnostic steps and verified BOTH my front resistors are shot. No low speed fan jumping the appropriate pins on R14 and R04. All the other tests passed. I've ordered 2 new relays and found some great posts on the replacement.

I also have an early 1995 w/ OBD1 and the Bergvill cable and software.

Here's my ? - should any codes have been thrown? I'm getting none. Wasn't sure if 41 and 42 should have been thrown? Doesn't look like there are specific speed 1 speed 2 codes for the front blowers - only the rear.

ToreB

The 993 CCU does not supervise the oil cooler and condenser fans, and fault codes 41 and 42 will never appear on a 993 CCU.

These fans are supervised in the Porsche 964, but the two CCU I/O-lines was used for the reverse gear detection input and outside temp sensor in the 993. I guess the engineers had long discussions on the removal of the oil cooler fan supervision circuit, it must have been a really tough decision.

Cheers,
Tore