I’m pretty new here but already I’ve learned a lot. I'm driving an '88 944na which is basically stock. Using the search feature I’ve found out how to repair my odometer and change my engine mounts, etc. Thank you all for the very useful information!

After changing the motor mounts this weekend, the car is now so quiet that I’ve noticed a hum coming from behind the gauges with the car stopped and the engine at idle. This is with the A/C and fan off. It sounds like it may be vacuum-related, but I don’t know what I should be looking for. Is this normal? Should I just install a radio and ignore the noise?

Another question is about my heater. It gets warm, but not hot. The turbo defroster from heck gets very toasty… but not the normal heater. Is there a specific sensor or valve I should investigate?

TIA!
-David

 

Odly enough, I've noticed a hum on cold startup that comes from the dash area... it goes away pretty quickly, but I think I'll pull out the stethoscope and see if I can find where it's coming from. It isn't very quiet though, like you were implying yours was.

Your heater should be burning your face... I wonder if your hum is related to that. The vents are controlled by vacuum... if there is a leak, and that's what you're hearing, they won't operate normally.

 

Thanks Kevin...
Yes, it's pretty quiet. I didn't even notice it at first. My girlfriend was sitting in the passenger seat and asked why the car was "whining." I wonder if it's related to the heater vent controls. It's not too tough to get the gauges out... maybe I'll have a look this evening. Maybe I can get under the dash with the gauges still in place and get a better idea of the source of the noise.

thanks,
-David

 

You know, the more I think about it (and I just went out to the car to verify), the more the noise sounds like an electric motor with a gear drive, just continuously running. Could it be one of the servos for the heater controls? It might explain why the heater doesn't work properly.

Any ideas? I guess I just need to rip the dash apart. I don't have a stethoscope and, as soon as I open the car door, the noise is drowned out by that oh-so-nice exhaust note.

There's an article on repairing 964 servos here: http://www.porsche964.co.uk/ which basically got me thinking along these lines.

Thanks again,
-David

 

This is a silly question, but do you have the defroster slide switch (in the middle of the front vents) pushed up all of the way to the top so that only the defroster gets the air? Just checking on the simple things first. This would probably not have anything to do with the hum though, just the vent heat.

I'm still waiting to use the heat down here in Texas.

 

Also, the heater control uses electric solenoids which control the vacuum to the different gates. When the controller goes bad, then you often hear an irritating clicking sound from between the heater controller and the glove box.

 

Hi Dan!
No, the defrost slider is fully down in the dash-vent position. I am all for checking the simple things first, since I'm new to this car (~1 month) and I don't know much about how its various systems work.

The sound I'm hearing isn't like a relay clicking on and off. It's a continuous noise, which seems to be located between the climate control unit and the instrument cluster. It seems to have two components... the first is like an electric motor "whirring" and the second is more gritty, like plastic gears not meshing well.

Maybe I'll be able to locate it if I do a little more investigation. I may need to pull the cluster, but I'll try sticking my head under the dash first.

Thanks for your help!
-David

 

Well there is (if I remember correctly...someone will correct me if I'm wrong) a small motor attached to the hose connected to the little round vent near the clock (about the size of a quarter). I think there is a small motor attached to that vent which pulls in air to check the cabin temperature. I'm on shaky ground here as I'm remembering this from about five years ago. Also, those solenoids click pretty fast although you usually don't get heat when you hear them.

 

Ok, it looks like I'll have to get a stethoscope.

I just crawled under the dash with the engine running to see if I could locate our little noise. I operated all of the sliders and *****, and the little electric actuators seem to be working fine. The temperature adjuster one is a bit slow, but maybe that's normal? The infamous "heater clip" was in astonishingly good shape.

The noise did not appear to be coming from any of the 3 actuators I could see (floor, defrost and temp. mixture). The noise actually seemed to be coming from further up and forward... near the point where the throttle cable passes through the firewall. Maybe it is coming from something under the plastic cover at the top rear of the engine bay? Maybe it's coming from somewhere else? It's like an echo chamber down there!

I haven't seen a little fan for the in-dash temp sensor tube... but that is a possibility.

The funny thing is that turning the temperature **** to full heat (red dot past 30 C ) results in only slightly warm air coming out the vents (regardless of which vents)... while pressing the "turbo defrost" button results in a great deal of heat... very warm indeed. Is there another actuator I'm missing?

What does the defrost button really do? I know it gives full heat, A/C and full fan... directed at the windshield... but does it do anything else?

Again, thank you very much for your time.

-David

 

on mine, the cabin fan still blows a very very tiny bit even when it is turned off, maybe that is what you are getting.

 

Patrat,
You know, I've noticed that on mine too... but I think this is something different. I suppose I could be hearing some crud somewhere in the squirrel cage blower or the ductwork. I suspect this one will take a while to figure out.

Thanks for the input!
-David

 

The fan stays on a very low setting even when the switch is off.... its in the manual.

 

Thanks, PennyWise.

You're right about the fan. However, the noise I'm hearing is only there when the ignition is in the "on" position (engine running). It's a little louder, and a different sound, than the fan on the very low setting. I wish I had a way to get some digital audio on it.

-David

 

Ok.. Still humming...Hmmm.. lets see. Can you identify the tune?