Rich W

Well, I don't - but my wife does!

Rich W

Update:

I've repaired the malfunctioning servos, and checked the remaining servos for proper operation. Servos are now functioning correctly.

When the defroster vents (and temperature cold) are selected I get air flow from the passenger side, but little to no flow on the driver's side (LHD). With the defroster button depressed, there is a little more flow, but the same distribution. With the temperature selected to maximum heat, there is flow on the driver's side as well, indicating the rear blower is operating correctly. The rear blower operation has also been verified at the engine compartment.

The LH fan appears to be operating correctly, as I can hear the air blowing through the fan exhaust plenum. The RH fan, however, does not appear to be working with the defroster button depressed. I have verified there is 12 volts at the leads to the fan, but was unable to determine if any air was blowing through the RH fan exhaust plenum.

Can anyone out there give me some additional guidance?

fcuesta

Hi Gentlemen,
Excellent info shared above. I'm a novice at this .
My question is I have a 91 964 Targa and really hot air blows out of the drivers side vent when the setting is set to cold and fan on 1 Center and passenger vents blow cold air from the outside like they should.

(no AC turned on. Its about 54 degrees outside and a bit cold) Are there any flaps or servos I need to unstick relating to that particular vent?
How do I access it? though the front hood, or under the dash...
Thanks a lot.

Take care,

Fred

fore!

Hi guys,

I've got the same heat dilema and I can't help thinking it all came around as a result of some @$%@^ tea leaf shattering a side window and sending glass everywhere. (all for a stinkin' radar detector!)

Anyway I know there's glass down inside the dash. I know there's glass in the hvac system - a couple of weeks back I had the heat problem, cycled the temp and distribution controls with the fan on full and could hear glass moving around inside the system. The air distribution system works well.

And now I can't get rid of the heat no matter what i do. I can get air from outside but it's being mixed with heat.

Anyway I have 2 questions - do we have the same heater servo's on the outside of the front footwells as in the 993s? (maybe theres glass pieces keeping them from closing?) And, is there anyway to access the system to get the glass out?

thanks

M - 93 RSA (red)

Adrian

Dear Fred,
Your drivers side mixing chamber servo vlave is stuck in the full hot position. This is as is described in this thread in the luggage compartment right up the back on the drivers side. You can pop the actuating arm off and set it manually to the cold position or any other position in between. You can even remove the servo and tie off the arm in the desired position whilst you fix the servo or replace it.

Dear M,
The system of air distribution is effectively divided in half. I suspect you have to look at this problem as a). servos which are in the luggage compartment and b) glass fragments which are inside. All I can suggest is that you make up a long thin hose (I did this once using heat shrink tube) and attach it to your vacuum cleaner. I actually shrunk the tube to the vacuum cleaner nozzle with a piece of dowel wood to make sure it did not close up completely. Use this thin tube to get into the vents and try and grab the glass fragments.
Ciao,
Adrian
964C4

fore!

G'day Adian,

In the dead of night when all was quiet - I checked the servo's and listened to them cycling. They all seem to do thier thing and produce the required air flow.

Good idea with the small hose on the vacuum cleaner.

The heat comes to the front of the car on both sides via ducting that runs up on the outside of the footwells. I noted in the 993 forum that they have a hot air supply valve in the footwell - do we have them too?

M

Adrian

Dear M,
The hot air is supplied direct to the mixing chambers from the differential pressure valves left and right.
The 964 has a footwell flapper valve which is servo operated but this is just to transfer heat to the feet. The ducting on the underside of the dash. It has nothing to do with the supply of hot air from the heat exchangers to the mixing chambers.
I re-read your post. To get rid of the heat you have to put the temp control **** in the blue dot position.
The other problem maybe that your rear blower fan is running all the time. This will also force heat forwards but if the mixing chamber valves are in the full cold position you should not get heat anyway.
I think you may have to exactly explain what your problem is so we do not head off on the wrong track.
Ciao,
Adrian
964C4

fore!

Adrian,

OK - I've down and dirty and checking things out.

With the temp set to minimum (blue) and both sliders on the left (closed) and recirc button off (outside air coming in) I can't get rid of the heat on the passenger side. Drivers side is fine.

M

fore!

All is OK again.

Pulled the r/h servo, took it apart, tested the motor OK. Checked the contacts - signs of burn!!

Clean off, reset tension, re-assemble, test and re-install. Ye ha!

That was easy. Thanks all.

M

fcuesta

Hi Adrian,

Thanks...This is a really great forum by the way. After taking the plastic protector off and exposing the servos, I noticed the driver's side servo was indeed stuck in the hot position and wasn't operating at all while the others did.

Pried off the control arm to air valve for the time being, took apart the servo and cleaned and re-bent contacts of the circular springy thingamajigs, reassembled and viola. It works again. Now if only I could readjust the control arm to *fully* close the air valve. I'm feeling a tiny bit of heat (better than last time) now, but I'm confident I'll get it right in a few minutes.


Thanks again!!

Fred

Jeff Curtis

RICH!! Shoulda brought it over...after all, you're only about, say 5 miles from me?

I'm glad I read through all the posts before replying, as I see that you figured out that the 993 servo (updated part) is delivered with the arm in the wrong position - easily adjusted.

Good job, I had the same issues a few years ago.

Now, when are we gonna pull out all your stuff to fix the condensor coils and make sure we have the procedure "down packed" before doing it on MY C2??

Bring it over and we'll get your servos in order...it'll cost ya some of this though:

Rich W

Another question:

Where are the "differential flapper valves" physically located within the system. I pulled the squirrel cage covers off to observe fan operation and motor operated flapper operation for heat, and all work fine. I'm still only getting defroster heat on the passenger side, with a trickle on the drivers side. It sounds like air is trying to blow past some kind of restriction, but I can't see it from the front due to the air conditioning condenser coil.

Any diagrams would be GREATLY appreciated!

And Jeff, if you are the first to supply one that leads me to the correction of this annoying problem, a six pack is yours!

Randall G.

Hey Rich,

I had this exact problem back in '97. Copied from my maintenance log on John Mile's website running reports:

"Diagnose problem with A/C, left defroster inop.—replace left mixing flap motor."

The shop also replaced the rear blower, but I think that was just a coincidence. (I had problems with blowing the fuse before.)

Are you sure the mixing flap motor is okay? In particular, when running the defroster?

What I think could be happening:

-Mixing flap is supposed to be positioned fairly wide open to receive heated air from the rear blower.
-Instead, it's positioned to receive fresh air.
-But...the fresh air intake is barely open. So, you get very little air at the windshield.

That's my guess, anyway.

No matter what, I'm sure the shop didn't mess with the differential pressure valves when they fixed my defrost.

Good luck!

Rich W

Randall,

Great info. I am pretty sure the mixing servo is working properly - I observed it operate the flapper that lets heat into the mixing chamber when I had the fan cover removed. I was getting the same effect at the windshield - little air on the driver's side, plenty on the passenger's side.

Yeah, I'm pretty flummoxed. If I knew exactly how the whole air blower assembly was configured, I'm sure I could figure it out, but...

Randall G.

Rich,

Sorry I can't be of more help. Perhaps you can double check the mixing servo, to make sure it's really working?

Suppose you can take a look at the differential pressure valve? You can see its exhaust in the rear wheel-well. I've never tried it myself, but it should be blowing lots of air if it's stuck in the dump-heated-air position (vented). Of course, the rear blower will need to be running to make the test valid. But, to be safe, I think you'll want the engine off. You might compare the left and right side differential pressure valves, to get a feel of what you should expect.

Roly has lots of great pictures of the disassembled HVAC unit which should be helpful. There's also a nice pic of the unit on page 334 of Adrian's book.