gpallem

Hi Everyone,

I am trying to find out why my heater blower fan (left hand side engine compartment) stays on continually these days; even when the engine is turned off. I had this happen once before, two months ago, but some "judicious wiggling back and forth" of the various components made it stop. This time, however, nothing seems to help, short of disconnecting the electrical connection to the blower motor--a must if you do not wish a dead battery (ask how I know . By now, I have found the blower motor to be somewhat noisy, which will probably lead to the oft-occurring seizing that I have read about in this list's archives. Before I get to that point, I will replace the fan motor--thanks to everyone that gave me pointers regarding this in a previous posting.
What I would like to know is what else I may have to replace at the same time, so that the new motor will also not continually run. Is it the resistor at the bottom of the heater pipe? Or, candidate number two, the pinky-like probe that sticks into the heater pipe half-way up? Or, something completely different?
Any insight is appreciated!

Just for the sharing of it: I have had this C-2 for almost three months and love it! I still also have my 84 Targa which I have had for the past 11-some years. Not until I drove the C-2 did I ever realize what a great car it is, and how it is a true improvement upon the 84-89 series. The C-2 feels quite a bit torque-ier (sp?), better dampened (especially up front), has much less body-flex (84 Targa vs 90 Cabrio), has much better venting/heating (aside from my blower problem , has an amazing transmission (pure joy to shift) compared with the 84 915 gearbox, has that great automatic spoiler that gives the other road users a visual treat, has in my opinion a more usable trunk (the 84's is flat front to back making you always worry about shifting groceries that will dent the hood), has done away with much of the gear whine and rattle, has airbags and ABS, and has the most perfect power steering. Before I drove the C-2, I was skeptical about these improvements, especially the steering. Now I realize that they are absolute refinements upon the theme. Was anything lost? Well, my 84 has a 22 gallon gas tank, and does have a delicacy of body lines that is somewhat less apparent in the C-2's. This is mostly because of the new bumpers which make the sides a bit more slab-like by interrupting the flowing edge of the wheel arch flares. On the other hand, the C-2 looks much more modern and updated as it doesn't sport the 12 square feet of black rubber that the 84-89-s do. Well, I could go on and on. Point is: I love the C-2.

Adrian

The most common cause of this problem is the temp sensor has shorted. I helped another 964 owner with this exact same problem a couple of months ago. You need to replace your sensor or check the wiring to ensure that the wires are not shorted out somewhere.
Put simply, your 964 thinks the engine is very hot and needs cooling down.
Yes this will flatten your battery in short order.
If you are asking, yes but the 964 has the ignition off. Yes this is true but the aircon/heating control unit remains powered for 20 mins after engine shut down to provide this engine overheat protection. If the overheat is not corrected the unit will remain powered until it is. In your case this means until the battery is flat.
The failing bearings in the motor play no role in the problem but you need to sort this as well.
Ciao,
Adrian
911C4

johnfm

Hi

I was the owner Adrian helped the other month. Its pretty easy to check the temp sensor with a multimeter - if it shows infinite resistance it is knackered! It was about £17 to replace in the UK.

Adrian

Dear John,
Or O ohms which means it is shorted. If the sensor is open circuit, the blower fan will never work because the sensor will be telling the control unit that the temp in the pipes is super cold,
Ciao,
Adrian
911C4

Randall G.

Hey gpallem,

Interesting that you also own an '84 Carrera Targa--that's the same model I owned before moving to my C2.

As great a car as the '84 is, the 964 is just better in (almost!) all ways. As you've pointed out, better shifting, faster, more comfortable and safer.

Funny you should mention the gas tank on the 964 being smaller. Yes, I do miss the extra 2 gallon capacity. I also prefer the '84's exhaust note. The 964 is a bit too quiet for my tastes. Then again, have you heard a 993 lately? Much quieter than even a 964. If there's one thing a 993 certainly doesn't have on a 964, it's exhaust note.

Enjoy your 964!

MattB

Hi,

I am the proud new owner of a 90 C4 Cab as of about 3 months ago, after parting with my 78 SC last year. I love the C4, but am running into the same problem(s) with the AC unit... Always on, and now I am hearing the tell tale sounds from the rear blower motor. I have ordered the replacement blower motor... Where is the temp sensor located? Does anyone know the replacement part number.

Matt

Jeff Curtis

Matt, first of all...congrats on making the switch to a 964, I've been tickled since.

The temp sensor is located on the plastic downpipe coming from the blower motor in the engine compartment. It senses heat coming up from the engine when you shut it off and keeps the fan on...blowing cool air through the heat exchangers, a valuable "assistance" tool in keeping your motor cool. To remove the temp sensor, just push down and twist 90deg. and pull it out.

BTW, noticed that you said you have a new blower on the way...I just replaced mine and have a few tips for ya:

1) The new blower motor is likely to be a 993 part...if so, you'll have to transfer the 3 aluminum spacers from your original motor, as the new ones are longer.

2) To facilitate downpipe to blower motor reassembly, slide the rubber sleeve for the downpipe all the way onto the downpipe, put lower end into the receiver in the engine sheet metal and line up downpipe to new blower motor, sliiiiiide the rubber sleeve into place and tighten the clamps...it's REAL easy.

MattB

Thanks for the tips Jeff. I also found a very helpful posting from Tom Sharpes with a link to a technical article (with useful pics) on Pelican Parts website that walks through the replacement process (http://www.pelicanparts.com/techarticles/964_blower_motor/964_blower_motor.htm).

I was aware of the difference in the length of the bushings, but not the downpipe to motor assembly tip - Thanks

Do you know the Porsche part Number for the temp sensor? or is there another description? The guys at Pelican were not able to find the part

Surfer2001

Hey guys I’d like to revive this topic once more, as I have this issue right now. I’m a little confused because some of the posts here refer to the rear blower (in the engine compartment), my problem is the AC/HEATER blower located in the front trunk, and the sound comes from under the windshield wipers. The fan stays on until I pull fuse number one.

Rocket Rob

Do you have access to another CCU? It sounds like you may have a fault in yours. Another option is to use a Scantool or hammer.

Porscheholic

Have you tried replacing the relay that is located in left side of the engine compartment? I had the some problem and that solved it for me.

Surfer2001

UPDATE: I talked to a local guy that has a business rebuilding Porsche CCU, he gave me some trouble shooting steps.
Pull the CCU out of dash and disconnect the unit, then check to see if the fan is still running. If it is the CCU is ok.

This means the blower amplifier is suspect.

This is a costly item and before going any further I’m suppose to unplug the blower and search for a short.

So far I’ve unplugged a few plugs and the blower stops, but I’m not sure what to do now.

boxsey911

For your information this is the blower amplifier. It's located under the scuttle panel (two screws to remove) in the front trunk near the windshield. You can see that I've unplugged it in the pic:



The usual symptom of this being faulty is that you no longer have control of the fan speeds when you turn the control on the CCU.

user 783003

The other day, my heater blower stayed on after I turned the car off. It was a hot day (90F) up here and I'd just driven 60 miles on the freeway, so I thought it may have been normal. Plus, it didn't stay on forever, just 10 to 20 minutes.

Today, it did the same thing (again in the 80's) when I got home from work. After having it parked for an hour, I drove a couple of blocks and it still stayed on. I checked a few things on the blower, disconnected, it, pulled it out, put it all back together, washed and dried the car. After it sat in the driveway for 2 hours, I pulled it into the garage and it still stayed on after pulling the key.

Just ohmed out the temp sensor (part that turn 90 degrees into the heater blower down tube) and it's open, infinite resistance. Based on what I'm reading above, that should mean it's very cold, and shouldn't run at all, correct?

Any suggestions? At what resistance does a normal temp sensor ohm out?

Is this related to my A/C compressor not engaging?

Rocket Rob

The heater blower running after turning the engine off is normal. If the outside temp is high, then it can run for up to 20 minutes. It was 95 yesterday and my car's blower was running when I parked it in the garage after driving home from work.