How to fix no HEAT from the central vent on BMW E36

One day I've found there was no heat air from the central vent,

so I spent some time checking it out.

I checked the Water Valve first.

Since it's a refurbished part and installed a couple years ago,

it's still clean inside and worked fine plugged with 12V battery [Pic 1].
Remember NOT to break the wires when assembling the part.

I also replaced the new Connection Flange and O-rings (EPDM) of the water valve [Pic 2].

When I tested for the first time, 

there was even no hot water in the water valve hoses. 

So I tried to bleed the radiator afterward.

After that, I got heat air from the side defog vent,

but there was still no heat from central vent.

I was so so frustrated.

I started to study all the documents about E36 IHKA and IHKR,

and I found there were flaps inside the air conditioner to mix the cold and heat air.

So I took off the cover under the steering wheel,

and tried to find where was the mixing flap motor (actuator).

I could feel the motor running when I turned the mixing dial,

but the flap didn't move at all.

I guess there must be something wrong with the motor.

However, I spent hours studying how to get it off.

Lastly, I followed what Bentley service manual said,

and just pushed the "CLIP" on the motor [Pic 3].

Luckily, I took it off and unscrew it to check it out.

It seemed that the shaft was pushed out too much [Pic 4],

so I knocked the shaft to push the gear inside.

After restoring all the parts, 

I got heat finally.

It was quite a journey to find out the answer to the heat.

[Pic 1]

[Pic 2]

[Pic 3]

[Pic 4]