DJR96

OK, so the problem is that I've got warm air coming through the main driver side vents when it should be cold. Passenger side is fine.
[It is the dual zone, single fan version of Climatronic.]
So system is gassed and does cool. Fan has all speeds as per normal.
Displaying the sensor data shows everything to be ok.

I believe it will be either-
a) the drivers side blend flap isn't shutting off the heat fully, or
b) the duovalve isn't closing when it should.

There is no clicking sounds so no broken linkages or actuator arms (I suppose one could have broken completely, not just cracked and clicking).

But before I rip into the dash I want to try the resyncing stepper motors procedure. My understanding is that simply by pressing and holding the 'recirc' and 'defrost' buttons will activate this procedure. But it doesn't, no alternating flashing LEDs on those buttons. What am I doing wrong?

Also, when I enter diagnostic code readouts, it doesn't show "diA" as most instructions say it should. It does show an "E", and presumably when no faults to show it displays "E FF". So it seems like it is in the right mode, just not displaying everything as expected.

Any assistance would be greatly appreciated!!

DJR96

Following on, nothing I do seems to stop heated air coming through.

I've checked the duo-valve (three port unit) and it seems to be in near new condition. No apparent problems at all. There is power at its connector and each coil is reading about 24.5 Ohms.

In desperation I've installed the springs on top in an attempt to make it default to closed, and disconnected the coolant pump. But it still blows hot air!!! WTF!!

MarcusF

Press and hold the "REST" button on the climate control. After approximately 5 seconds, the display will change. You can now release the REST button. The left "auto" button will allow you to scroll through the menu. #01 will show you the temperature inside the car. #03 will display the temperature of the left side heater core. #04 will show the temperature of the right side heater core. #05 will show you the temperature of the evaporator sensor. If the heater is off, hot engine coolant should not pass through the heater cores and #03 and #04 should be very close in temperature to #01. If #03 is hot, the duovalve is probably letting coolant through.

DJR96

Hi Marcus, it didn't matter what I did I could not get the duo-valve to shut off completely. It appeared to be in great condition. For the moment I have removed and re-inserted the two brown plastic sleeves 180 degrees around such that the opening in the side is opposite where they should be. This has blocked coolant flow.
Which has allowed me to continue diagnosing the AC system. Which was low on gas. Not so low that it would shut down, just too low to be effective. So I've topped it up for the time being. We'll leave it for a few months and see if it leaks out. At least it'll be cool for summer - we're expecting 36 degrees C today!

Next time I open up the duo-valve I'll turn the sleeves back to where they should be. All I can think of is that the poppet valve seats are worn a bit and the solenoid doesn't have the stroke long enough to seat the valve properly. So I'll try putting a small plastic washer over the poppet valve pins to act as a spacer to ensure the solenoid is actually applying pressure on them to close properly. Even just 1mm thickness could make all the difference. I'll have to report back on my results.

Serndipity

DJR96, The blend and diverter flaps, in the air outlets, are vacuum actuated, so I'm confused as to what stepping motors you're attempting to reset/resynch.

What were your results from running the Individual Flap Test, via the N22 Pushbutton Control Module?

In your A208 cabriolet, are you running the HVAC system, in automatic or manual operating mode?

Also, when you ran the N22 Pushbutton Control Module diagnostic tests for the HVAC system values and trouble codes, was you roof open or closed?

While your malfunction is much more likely to be related to another component in the HVAC system, here is an explanation of how the duovalve operates.

The duovalve controls the quantity of coolant flowing through the left and right sides of the heater core.

When the heat requirement is low the pushbutton control module switches the duovalve solenoids to ground, the solenoids pull in and block the coolant
flow to the right and left sides of the heater core separately.

At the maximum temperature setting the pushbutton control module interrupts the ground connections current no longer flows through the solenoids, and
the coolant flow through the heater core is at its maximum.

During normal regulation the pushbutton control module completes and interrupts the circuit to ground intermittently. The closing and opening times for
the duovalves depend on the deviation between the temperature present on the interior sensor and that set on the pushbutton control module.

DJR96

Everything always done with the roof closed. I am aware some things don't work when the roof is open.

I thought all the flaps are operated by stepper motors, no vacuum bits at all. Or am I wrong here?
Anyway, I seem to be able to get airflow out everywhere as intended. Although, during the flap test mode it never actually closes everything as per test 0 and 15. There is always airflow out the side vents on the dash.

I did end up inserting a small plastic disc onto the stem of each of the poppet valves in the duo-valve. This seems to have done the trick for now. It means the plunger is able to push the valve a bit further against the seats and block coolant flow. The seats must have just been a bit too worn before.

I think I have a fully operational HVAC system now. Time will tell.

Thank you gents for your input. Hopefully this thread will be helpful to others too.
Cheers.