Thermador T36IT800NP evaporator ices

[wddanie]

My 10 year old Thermador T36IT800NP makes a ticking noise and I found it is ice forming on the refrigerator evaporator coil, which contacts the fan to make the ticking noise. I researched this and it seems to be a pretty common complaint but I have not found postings that list what the solution finally was. I replaced torn door seals, ran the service program and the sensors are giving accurate readings. The heater defroster measured 93 ohms and the heating element was 576 ohms, which matches the values I found in an online service manual. The temp limiter measured closed. I ran a wire down the drain tube and did not feel any obstruction. I fired up the defrost heater with the service menu and I felt it get warm, but it only stayed on for a few seconds and did not feel very hot to my fingers.

The ice on the evaporator is mostly clear, but they are some white spots scattered in the ice block. 

I can't find anything obviously wrong, but I am a DIYer and think someone more experienced will know what is the likely root cause. I would prefer not to throw new replacement parts at it when I can't detect a failure. 

After melting the ice with a hair dryer, it runs fine for about a week, then I hear the ticking and have to manually defrost it again. 

Could it be a problem with the sealed system? If so, I think I am within the 12 year warranty and might be able to get Thermador to cover the repair cost.

I attached a few pics.

Thanks in advance for your help!

[BrianG]

System is low on refrigerant. Parts are covered for 12 years.

[wddanie]

Brian, Thanks for the advice! Do you think Thermador figure out where the leak is and fix it or will they just add some coolant? 

[BrianG]

Usually the leak is in the coil or the capillary tube by the coil. In your case I bet it’s the coil. You’ll also need a new compressor and filter drier. You’ll want someone experienced doing the repair or they can make a mess of things pretty quickly. 

[wddanie]

Thanks for the insights! I will shop around for a good Thermador dealer in ATL. Do you happen to know anyone here?