Tony993

I'm a new member and this is my first post... and I could really use some help.

I have a problem with hot air always coming out of the right side vent, the left side is OK and blows cold air. I've already searched the 993 forum and have tried a couple of suggested fixes. First, I replaced the flapper control motor with no effect. Then I replaced the temperature sensor in the right mixing chamber but the problem persists.

When I run Durametric's scanner s/w attached to the OBD II port and check the A/C it still shows fault 32 Right Mixing Flap Motor.

Does anyone have any ideas what I could check next?


Tony

Falcondrivr

It sounds basic, but you checked that the vacuum lines were hooked up and leak free to that servo right?

Tony993

Hi Rick,
Thanks for the quick feedback. The servo motor driving the vent flap under the passenger side dash didn't have a vacuum tube. Should I be looking elsewhere for a servo/vacuum tube?

Tony

KASH '95 993

I have been having the same issues also, however, it corrects itself when I quickly switch back and forth between hot and cold settings on the climate control dial after about six or seven times within about 2 to three minutes...PITA.

ToreB

The hot air flap is not at all vacuum powered, it's got a an electric servo mecanism. You should see the rotation movement on it when you set temperature to minimum and maximum.
I also believe you have replaced the correct flap servo? The one that controls hot air on the right hand side of the dash is placed behind the kick carpet cover in the right footwell.
If so, and the servo is inert, you may have a problem with the driver IC/circuit inside the CCU for this servo. I have seen some posts here that indicate that defective servos can destroy the TCA2465 driver.
See here:
http://www.porsche964.co.uk/technical/climate.htm
Regards,
Tore

Tony993

Hi Tore,
Thanks for the help. I'm confident that I replaced the correct servo motor. Actully, when the new one didn't work on the RHS, I checked it out by plugging it in on the LHS. Both my motors open/close just fine when plugged in on the LHS. So the motors are good and I've since replaced the RHS temperature sensor. So, I think you may be correct about the CCU being bad. I'm going to pull A/C Regulator out of the dash and see if I can check out the G & K connector input/outputs with a multi-meter. I found some details about how to do this in the Porsche993Manual.pdf file on page 80-20 (absolute page # 1451).
Thanks
Tony

ToreB

Very good Tony.
I've repaired a few of these CCU's, and in two of them there were brownish burn marks on the PCB around the defective TCA 2465 driver. It's easy to pop the unit open to hat least have a look. If you do, remember do undo the four screws on both connector assemblies at the back. You can then remove the two metal housing halves.
I pulled out the spare part IC from a fellow Porsche club member's defective CCU unit, they are obsolete, and not easy to get hold of.
Regards,
Tore

Dudley

I was over to my mechanic (EPE in Natick - the Best) a couple weeks ago to have my car checked out.
Jerry hooked up a Hammer and he was satisfied that there were no issues. The cool thing was he could test the operation of each fan motor and each servo as we stood there. If you have a local independent, it would certainly be worth your while to have him check out the systems on you car.

Tony993

Tore,
I've taken the CCU out of the car and have it in pieces in front of me. It's not easy to view the four TCA2465 chips because the top and bottom circuit boards are soldered together at three location. They are about 3 cm apart and they face each other. However, I don't see any obvious 'browning' of any of the four chips. Do you know if I could test these with a mulit-meter and what readings I should get?
Regards
Tony

ToreB

Hi there, it is difficult yes. I were lucky to see a veeery faint brownish colouring on the PCB around the solder leg row under one of the TCA's. That was visible from the solder(outward) side. Also, most of the solderings on that IC had gotten somewhat dull due to the heating, and had not the shiny solder "blankness".
Maybe you're not that "lucky" to have had overheating inside your CCU mate. I have no schematics of the inside of the CCU unit and do not know what IC that controls what servo.
We maybe could find out by tracing the control wires to the connector on the CCU, and then follow the PCB tracks.
That would maybe require to separate the two PCBs, and some digging in the car wiring schematics.
Regards from
Tore

Tony993

Hi Tore,
Thanks again for continuing to help. Visually tracing the circuit board from chip to the correct pins on the G & K connectors sounds tough!
I did notice something else though. There are four TCA2465 chips in locations IC12, IC11, IC10 & IC9 on the printed circuit board. My IC11 chip appears to be of different vintage than the other three! I wonder if this has previously been replaced. Can you remember which one you replaced and which of the vents it controlled? Perhaps this could help my process of elimination. If I can identify which chip drives the RHS vent motor I could just go ahead and replace it. If I do that and it still doesn't work it may be time to look for a refurbished CCU.
Regards
Tony

ToreB

No prob Tony, this is good fun.
Sorry, I can't remember what IC I replaced and what servo that didn't work.
Following the PCB tracks wouldn't bee that difficult, if we identify the connector pins, a multimeter with a diode/beeper tracer would easily trace the right connections. Following the tracks on the PCB may not be necessary. I'm sure the output of the TCA (pin 2 and /or 9) is directly wired to a pin on one of the connectors, maybe some of the inputs as well, as the servo is some kind of locked loop thingy. I would compare it with a regular RC servo.
You find a PDF data sheet of the TCA by Googling it.

Well, this seems like fun and a challenge for me, I'm an experienced electronic engineer. Please exuse me if I'm diggin into this too deep with you in front Tony...
All the best,
Tore

ToreB

As far as I can see on these schematics the following is the goodies:
Yellow/Grey wire --- K/17
Grey wire --- G/8
Black/Grey --- K/4
Where K is the 25 pin connector, the 35 pin larger one is connector G. That's noted beside the CCU "box" on the schematics.
You should be able to find a connection from one of these pins to one of the TCA IC's, pin 2 or 9. As I mentioned, the easiest way would be to use a multimeter with ohm-meter/beep test function.
TCA 2465 data sheet cutout:

993 A/C schematics:

Good luck Tony
Tore

Tony993

Tore,
Based on Porsche993Manual.pdf
G8 = RH Temperature Mixing Flap Potentiometer
K4 = RH Temperature Mixing Flap
K17 = RH Temperature Mixing Flap
Here's what I found out with the multi-meter:
G8 - does not BEEP with any pin on any of the four ICs
K4 - BEEPS only with pin 9 of IC10
K17 - BEEPS only with pin 1 of IC11
I'm not sure what this suggests... does it use more than one TCA2465 to control the RH Mixing Flap Motor?
Regards
Tony

Tony993

Tore,
Perhaps I should also test for continuity between G8, K4, & K17 on the plug-in connector (currently hanging out my dash) and the RH Flap Control motor in the passenger side footwell. Just to make sure the wiring harness is ok before I start to remove/replace ICs in the CCU.
Regards
Tony