Defrost cycling causing condensation inside chamber and then causes ice buildup

During the defrost cycle, does the H-42 ever change or does it say that the whole time?  Also, what is the display saying temp inside the cryostat?

How is the seal around the window? It may be sucking in humid room air when cooling down and condensing inside the chamber. Much like a fridge with a bad door seal will grow a puddle or the freezer fills up with ice.

Thank you for responding.  I wanted to go back and observe a full defrost cycle but since it was lasting too long, greater than 45 minutes,  I interrupted it.

As soon as the defrost cycle starts, within the first minute H-42 shows up on the temperature display and remains there throughout the defrost cycle.

After the first 5 minutes the temperature in the chamber as measured by my own thermometer was -11C.

After 21 minutes it was +2C.

After 25 minutes it was +4C.

At this point condensation started appearing on the window and on the microtome surface inside.

The window insulation looks secure since we do not see any issues once the cryostat cools down to -20C, there is no frost buildup inside or around the edges.  

Ok, it would appear that the temp sensor for the defrost cycle is broken, thus the defrost cycle is running too long and it is causing this ice and frost issues.  This sensor is difficult to obtain, if you need assistance on that please let me know.

Can you tell me where the sensor is located and how to get access to it?  This issue started shortly after someone did preventative maintenance on the cryostat so maybe the sensor has fallen off or the wire has been damaged.

It is highly unlikely that this happened during the PM is the sensor is not easily accessible. It is located in the evaporator and requires taking off the top.  I recommend that a service tech do this repair.

Also, this sensor is not readily available as parts have been discontinued for this model.  Also, it is not a generic sensor like some models.  If you need assistance with the repair or obtaining the part, please email me.

Thank you for all your help.  I have a repair tech coming in next week and will discuss it with him and let you know if we need assistance with obtaining the part.