Hi @gusf ,
It seems to be a problem with the sealed system.
You said that there was no ice build up on the evap unit but is there ice build up anywhere else e.g. pipes into evap unit from condenser or into compressor from evap unit etc which may indicate restricted flow?
Being intermittent makes it difficult but I’m wondering if perhaps you have a clogged filter dryer that is restricting the flow occasionally.
Perhaps high and low pressures in the sealed system needs to be checked when the temp is warm and the compressor is running. I don’t know how it is where you are but here you need a licensed repairer to service the sealed system due to the environmental regulations regarding the handling of refrigerant gases.
Also here’s the service manual that may help as it has the parts list and shows locations etc of all the parts.
It also details how to perform a manual defrost as I was wondering if you can make it happen by doing a manual defrost and check if it happens shortly afterwards.
I realize that you said the defrost is OK but I’m wondering that if there is a restriction in the sealed system e.g. at the expansion valve or in the filter dryer due to floating sediment in the system.
It may be more noticeable after a defrost as it has had time to settle and cause the blockage as there has been no compressor pumping the refrigerant through the system during the defrost rather than when the compressor has been working for a long while so the flow is continuous and keeping things moving so to speak.
This may be also occurring when the freezer reaches the set temp in that the compressor will be turned off and only turned on again when the temp in the freezer needs to be driven back down again as it has risen above the required set temp range i.e. no refrigerant flow occurring in the system the same as when in defrost mode.
If you try this don’t let the defrost occur for too long so as to not damage the evap unit by letting it get too warm. Most defrost cycles are for 15-20 minutes but your model may be different.