ataman

Everything was OK concerning my air conditioning and heating system until today. Since my old CCU had not worked; I replaced it with a brand new CCU four months ago.

When I started the car today morning, the heating system did not work. When I hit defroster switch, there was no air coming to my front window. Terrible driving experience

At the moment the CCU system report is:
1. Defroster does not work, no air is coming from dashboard air opening slids to windscreen. Whenever I hit the defroster button, it increases blower speed to the maximum but the air is coming only from dashboard vents(left, right and center) and the air is not warm, just regular temperature.
2. No heating - eventhough I turn the **** to maximum heat position- red dot- no change!
3. I can not divert the airflow to the foot area - it seems that air distrubiton slide control buttons can not operate the system
4. Blower speed selection switch is working properly
5. Cooling function also seems to be affected. No cooled air.
6. I checked the fuses and relays, all of them is OK.

Do you think my CCU is kaput again? If you think so, do you have any explanation why CCU unit is affected so frequently?

I read many post regarding servo motor and valves; but I am totaly confused.

Any comments will be appreciated.

Ray Calvo

Might suggest checking all the vacuum lines in the engine compartment. If you lose vacuum, as I remember the air distribution system will shut off all outside air supply (even to the center vents, so maybe this is not your problem).

With the engine idling, check the vacuum line around the right-side engine air intake duct (between the air filter and the intake manifold). When I brought my '95 in for the wiring harness repair, dealer never reconnected this line connection. I have also had the solenoid to the left of the engine cooling air inlet /alternator fail and cause a vacuum leak.

As far as the CCU, can only suggest to see if anything is wired into the same power supply (radar detector, CB radio, cell phone, phaser cannon, etc.). Could be causing interference and failure of the CCU.

Randall G.

Hey Ataman,

Sounds like none of your servo motors are responding to CCU requests. The 5 servo motors being:

1) Fresh air intake
2) Defrost/dash vent selection
3) Footwell vent
4) Right mixing chamber flap
5) Left mixing chamber flap

#1-3 are under the flimsy black plastic cover in the luggage compartment, at the base of windshield. Pull the cover off, and watch to see if any of the servos are responding when you move the CCU sliders, or press the recirculation button (fresh air intake). I suspect they aren't.

#4 & 5 are in your footwells. Again, change the temperature control **** setting, and see if they move. I suspect they won't.

All of the above servo motors share the same position sensing reference voltage from the CCU. Soooo... a problem with the reference voltage will cause problems with all 5.

Just to eliminate it as a possible (though, highly unlikely cause), verify the rear blower in the engine compartment is running when you request heat. Say, interior fan at 1, temp. control **** set all the way to red dot (clockwise).

As Ray suggests, you can also check for vacuum leaks. But, a vacuum leak should not affect your servo motor controlled mixing chamber flaps. That is, I don't think it would affect temperature control.

Well, this is a start. Let us know what you find.

ataman

You are right, they aren't.
#4 & 5 are in your footwells. Again, change the temperature control **** setting, and see if they move. I suspect they won't.

All of the above servo motors share the same position sensing reference voltage from the CCU. Soooo... a problem with the reference voltage will cause problems with all 5.

Just to eliminate it as a possible (though, highly unlikely cause), verify the rear blower in the engine compartment is running when you request heat. Say, interior fan at 1, temp. control **** set all the way to red dot (clockwise).

As Ray suggests, you can also check for vacuum leaks. But, a vacuum leak should not affect your servo motor controlled mixing chamber flaps. That is, I don't think it would affect temperature control.

Well, this is a start. Let us know what you find.

ataman

Dear Randall,

Here is my report according to your instructions:

1. You are right. All of 5 servos do not respond to any CCU commands.
2. Rear blower in the engine compartment is working properly.
3. I checked any vacuum leak as Ray suggests. There is no vacuum leak.

Randall G.

Hey Ataman,

Definitely sounds like a problem with the reference voltage.

The fixed reference voltage is placed across a separate resistor for each servo motor. There's an electrical pick-up that moves across the resistor, as the servo motor/flap moves. The CCU senses the voltage on this pick-up. At one extreme end, it reads 0V. At the other extreme end, it reads 5V. In-between, it reads some value between 0 and 5V, the value telling the CCU where the flap is currently positioned.

If you can find the electrical connector to any of the servo motors, you can check for:

*5V between pins #1 & 2, ignition on.
*Ignition off, check for continuity between pin #2 at the servo motor plug, and G13 on the CCU plug. Unless you're testing the fresh air-flap servo. In which case, pin #2 should connect to G18 on the CCU plug.
*Ignition off, check for continuity between pin #1 at the servo motor plug, and G18 on the CCU plug. Unless you're testing the fresh air-flap servo. In which case, pin #1 connects to G13 on the CCU plug.

Best of luck!

ataman

Dear Randall,

Thank you for your help and instructions.
1. How can we explain that everything was fine until yesterday? The car was in my garage. No handling, no accident so on.
2. Why there is no heating and cooling in the system?

Regards,

Randall G.

>1. How can we explain that everything was fine until yesterday? The car was in my garage. No handling, no accident so on.

Sorry, no idea. If you are in fact experiencing a second CCU failure so soon after having it replaced, it certainly isn't normal. Perhaps some aftermarket component hooked where it shouldn't be, as Ray suggests, I really don't know. Maybe just really bad luck?

>2. Why there is no heating and cooling in the system?

Because your temperature mixing servos aren't repositioning the mixing flaps. The mixing flaps are used to mix heated air from the heat exchangers and cool air from either outside or inside the car. Without repositioning, you're getting whatever mix they're stuck at. Which is probably luke warm...

Are you going to try checking for proper voltage and continuity?

ataman

Of course, I will check for proper voltage and contuinity. Actually, I have already begun to check the servos for
1)Fresh air intake
2) Defrost/dash vent selection
3) footwell vent
with ignition on -engine off- position. There were no voltage, I mean 0V.

Then I thought maybe I have to check them with engine running position. Guess what, battery went to flat I put trickle charger (Porsche Battery charger to cigarette lighter). I must wait for until the battery recover itself.

I am not sure that during my voltage checking test whether CCU was on or off. So I think, I have to test all system again according to your instruction. I will let you know test report as soon as I have.

Meantime, if I find 0V at servo's pins #1 & 2, what does it mean? Just out of my curiosty.

Regards,

Randall G.

Hey Ataman,

If the interior fan will run, then your key is in the correct position, and the servos should be powered.

0V between pins #1 & #2 means your CCU isn't providing a 5V reference voltage for the servo/flap position. Or, there's an open on sensor ground (G18). If you get 0V between pins #1 & #2, you can try checking voltage between pin #2 (or pin #1 for the fresh air flap) and a convenient ground. If you get 5V, then you have a problem with sensor ground G18.

If you want to get kinda' tricky, you can try disconnecting the arm off of one of the mixing chamber servos, and manually positioning the flap to see if you get hot air. Of course, you need to do this with the engine warm, or you won't have any heated air, anyway.

Best of luck!

ataman

Dear Randall,

This is my test report according to your instructions.

First of all, I could not test the servos of the Right & left mixing chamber flap because I could not reach them. The data which I provide you is related to the servos of fresh air intake, Defrost/dash vent and foot well vent.

1. The voltages between pins #1 & 2 are 0V when ignition on. I measured also during engine running position. No changes, the voltages are again 0V.
2. The voltages between all Pin #2 (and also Pin#1) and a convenient ground are 5V.
3. Ignition off, the continuities are intact. I mean there is no disconnection between:
a. Pin #2 at the servo motor plug and G 13 on the CCU plug for foot well and defrost servos.
b. Pin #2 at the servo motor plug and G18 on the CCU plug for fresh air servo.
c. Pin #1 at the servo motor plug and G 18 on the CCU plug for foot well and defrost servos.
d. Pin #1 at the servo motor plug and G13 on the CCU plug for fresh air servo.
4. My interior fans work properly and they respond to CCU’s command.

I am waiting for your comments and instructions.

Many thanks and regards,

Randall G.

Wow, that's great work, Ataman! In particular, very interesting that you were able to get 5V when using a convenient ground. Sooo.....your CCU is putting out 5V, but the sensor ground inside the CCU appears to be open. Thus, no complete circuit for current flow.

>2. The voltages between all Pin #2 (and also Pin#1) and a convenient ground are 5V.

Just to be absolutely clear, when you said you got 5V at pin #1, you meant only with respect to the fresh air flap, correct? If you have 5V at both pins #1 and #2 for all servos, that means you have a short between G13 and G18. If so, I'm surprised a fuse hasn't blown.

It's a long shot, but you may be able to open your CCU, and figure out where/if there's an internal break on the G18 line (assuming you don't have a short between G13/G18, as described above).

I'm a little surprised you're not experiencing problems with other components that use G18 sensor ground, e.g.: the oil cooler temperature sensor, the rear blower duct temperature sensor.

Getting creative here.... If the 5V is only present when the ignition is on (and, again, assuming you don't have the short described above), you may be able to splice the G18 wire to ground. And, I think everything would work like it's supposed to. Of course, if the 5V is always hot (ignition off), this would create an ignition-off battery drain.

Finally, here's an excerpt from the HVAC electrical diagram. From this, you can see where you were measuring between pins #1 and #2, and how you should have found 5V across the pins. You can also see the servo motor power (pins #4/5) and position sensor (pin #3).

http://members.rennlist.com/rgranaas...Schematic2.jpg

Hope this helps, and please keep me posted on what you find.

ataman

Dear Randall,

I did all test again in order to be sure what I did yesterday.

1.I found 5V at both pins (Pin#1 and 2) for all servos, including fresh air flap. I thought I was going to find a short between G13 and G18 in CCU. But!
2.I removed CCU from dashboard and opened it. There was no short between G13 and G 18, strange!
3.Then I checked G 18 electric line on the circuit board of CCU. Oops there is. I found a gap (disconnection) on it. Using with a wire, I closed the gap and everything begun to work as it¡¦s supposed to.
4.At the moment, my air conditioning and heating system works without any problem. Thank you.
5.Now, we have to find what caused to this gap, in order to prevent another CCU depended problemļ let me remind that the CCU is a brand new. I changed it four months ago.

Randall, I really appreciated your help and patience. Without your help, definitely, I would not solve my problem.

Many thanks and regards,

Randall G.

That's great news, Ataman! Bet it feels good to have it fixed, I'm glad I could help.

Odd that the G18 line would develop an open so soon, being a brand new unit. Maybe just (real) bad luck. Hopefully, your repair will be permanent, and you won't have any CCU problems for a good long while.

Enjoy your heat!