speedbagger

hate to post another rear blower question but now that i've perused the first couple of search pages it's still not clear to me what constitutes proper operation...

if i understand correctly (please advise if wrong or somethings missing):

1. blower has multiple speed settings (not sure how many or if variable)
2. blower can engage as required by tube temp sensor (not sure what temp)
3. blower should not come on with temp dial full cold/blue (unless requested by point 2 above)
4. blower can run up to xx minutes post ignition off if temp sensor requests
5. blower should not engage on cold car during key on (no ignition)

my car is exhibiting number 5--when i key on (but not start) the blower immediately goes to what i'm assuming is high and stays on. it does not, however, stay on when i key off.

plan on checking the resistance to the temp sensor tonight but wanted to be clear on proper function before trying to diagnose.

one last question regarding the two sensors on the blower tube...how do the 'outer sensor' 964 659 120 00 and series resistor 964 616 550 0X function? in other words, what are they controlling?

i know--probably time for me to buy a manual....thanks in advance.

crg53

#5 is perfectly normal, when you turn on the key, the ecu go through a bunch of checks including the resonance valve and rear blower motor.

PS: The resistor controls high/low speed of the fan, the temp sensor turns on the fan when a certain temp is reached in the tube.

Compliments of Tore: SCROLL down to rear (aux) fan.

speedbagger

crg--thanks, but should it stay on if i don't start the car?

to clarify, if i key on only (no ignition) the blower turns on to high. then the blower turns off (for maybe half a second). then the blower turns back on to high and stays on high until i key off.

ToreB

crg53, thank you for your compliments.
speedbagger, you probably have a faulty rear fan low speed resistor. All details on this are given on my web page linked above.
Cheers,
Tore

speedbagger

toreb: great site. thanks for the link and your work.

neffets

Here is all you need to know about the operation of the fan
Under Rear aux fan
http://www.bergvillfx.com/porschehvac2.html

crg53

Neffets, click on SCROLL in post #2.

Hobbsie

On my 1990 C2, the engine blower runs on slow for 2 seconds, then off for 2, then on, etc with KOEO (key on, engine off), engine cold. Unplugging either resistor or sensor on pipe make no difference. All controls on CCU are off. Does this ring a bell with anyone?

ToreB

Rear fan cycling on high speed indicate the need for either resetting the thermofuse or changing the complete rear fan low speed resistor. I always change them these days.
Cheers,
Tore

speedbagger

ok, so problem just moved on me....

i changed the speed control resistor and my motor went from high to a lower speed during key on.

thought that was that until i keyed off (never turned ignition on) and the blower motor stayed on. it was not doing this before installing a new resistor--even with the engine warmed-up.

suggestions for whats next? relay or temp sensor (or just get both)?

pi5tolpete

My problem was the wire break at the NTC sensor. It was going to fail safe and making the CCU think the engine was hot and staying on for 20 minutes. All fixed. I have a post on this back in April 2014

ToreB

speedbagger, the rear fan shall run on low speed if you have set the temperature and fan speed controls to higher than minimum.
Cheers,
Tore

speedbagger

tore--understood, but maybe i wasn't clear...

i have the fan on zero and temp full cold and the blower runs after keying off a cold engine (never started).

pulled relay for now.

Hobbsie

Tore, I had written:

"On my 1990 C2, the engine blower runs on slow for 2 seconds, then off for 2, then on, etc with KOEO (key on, engine off), engine cold. Unplugging either resistor or sensor on pipe make no difference. All controls on CCU are off."

Am I understanding you that blower operation I am experiencing is same whether resistor or temp sensor connected or unplugged?

ToreB

Hobbsie, I would guess your rear fan is cycling on full speed, not low. Unplugging the fan low speed resistor will disable low speed operation. If it still runs with the resistor out, it must run on full speed.
I would start with checking the resistor and temperature sensor with an ohmmeter.
Cheers,
Tore