Frost-free freezer "modification"

[VanMarco]

HELLO!
I bought a freezer today at the usual store that sell used/refurbished ones. here where i live there are many shops that import appliances from Germany and fix it and resell it. I have already bought 4 from them, unfortunately one died recently and i needed urgently another one.
I didn't want to buy another 25 years old one, even though very reliable, the gasket can be ruined.
They had some nice frost-free ones, but, none, the electronic board worked. The price was quite low though, so I bought one.
They call these "modified". Essentially, the electronic board that controls the freezer is faulty, so they simply bypassed it, using a regular mechanical thermostat (which I plan to replace with a nice electronic one with numbers and all) and a defrost timer.
Now for me it does not matter if the board is not working anymore, but am I going to encounter any issues or downside of this mod?
Thank you in advance.

[helius]

The electronics are unnecessary for a fridge or freezer to perform its functions, as the older models didn't have any. A bimetallic thermostat and mechanical defrost timer should work fine and are much more reliable.

[VanMarco]

ah thanks, i also figure that in theory it would be better, as those parts they used, are simple and common to find a replacement for, my other miele freezer got faulty, the part costed 40 euro yes, a simple ptc probe.
sorry for the weird question, i bought based on general condition, gasket is new

thankssss

[helius]

You can check that the condensor coils are getting hot and the inside and outside fans are running, and that the compressor pump starts smoothly. That pretty much covers the mechanical aspects.
If the compressor's start capacitor is weak it may not start smoothly. Replacing the capacitor (or replacing it with a higher value) is very simple.

[amyk]

The electronics are unnecessary for a fridge or freezer to perform its functions, as the older models didn't have any. A bimetallic thermostat and mechanical defrost timer should work fine and are much more reliable.

Agreed; a mechanical thermostat has far less to go wrong, and when it does, is also much easier to fix. A lot of fridges from the pre-electronics era are still working perfectly well today.

[VanMarco]

I collected the freezer today, the defrost timer is like this
it is set pretty much like the image, just a few teeth down per 24 hours, is it normal to defrost this little every day?
Thanks.

[Seekonk]

Normally what happens is the mechanical timer is connected to the thermostat power out.  This gives compressor time on the timer.  So, every 24 hours of compressor time the heater will turn on.  This is also connected to a relay so when the heater is on, the compressor is off.  Once the heater turns off the compressor will run till down to temp again. 

With that timer you could also do defrost every 12 hours or other time period depending on how much buildup you get.

In series at the heater is another sealed thermostat.  That opens when the coils reach a temp over freezing.  These tend to fail a lot so make sure the heater circuit has continuity once down to temp.

[VanMarco]

Thank you Seekonik. i checked what the mechanical thermostat does, i remember those to be very inaccurate, even having a difference of 5C or more, this one does like -21 off, -19 on, is it possible they can be really that accurate???

[VanMarco]

I may have found a problem with the MOD.
Normally, it was fine, one time I open, and there are iced drops of water from the top evaporator, and on the door, right in front of where the evaporator is.
I suspect that when the defrost cycle is carried out, the fan is not actually turned off.
I will verify this today, but if that is the case, it means i need to put a relay in such a way that also the fan shuts down during defrost?

[VanMarco]

I did check this today, apparently the timer does nothing more than leave both compressor and fan off for 45 minutes.
the ice i found, I have no idea where it comes from, maybe the gasket?

[helius]

It could be that the drains are plugged up. Inside the evaporator chamber, are the fan, defrost heater, and a drainage channel. When the ice is melted off the evaporator, it runs down the drain and should pour into a pan near the condensor (this provides extra cooling effect from the water vapor to the condensor).

Defrosting turns on a heater, which you should be able to measure if you have a power meter (Kill-O-Watt, etc). The power used by the defrost can be more than the cooling cycle.

[VanMarco]

Hello.
I am rewiring the thing correctly and decently, as it was really badly made. I have uploaded pics of inside the evaporator, as i wanted to know which cable goes where, now that i checked, other than i found a huge lot of electrical tape in a high moisture environment, i found these two parts that i have no clue what they are. if you read the exploded view the red part that i dont understnd what it is should be 0140, listed as "NTC sensor" but the white part that looks like a cap, I cannot find it.
https://imgur.com/a/bgel63r
exploded view https://www.siemens-home.bsh-group.com/uk/spareparts/media/58300000195577_aet_000_a_01.png?dataPk=9382965968926&width=1442&height=1019
it appears the red part is some sort of sensor for temp, it should be 25C one like this. https://sajjs.com/en/sensors/112-sensor-refrigerator-bosch-480132103383-whirlpool-sensors-whirlpool-nr57180.html
So do you know how do I wire this correctly, and most importantly, how do i avoid moisture going into the connections?

[helius]

The 25°C sensor is described in reply #6 by Seekonk:

In series at the heater is another sealed thermostat.  That opens when the coils reach a temp over freezing.  These tend to fail a lot so make sure the heater circuit has continuity once down to temp.

Making the connections moisture-safe is a good use for silicone dielectric grease. Put a little grease inside plug-in terminals and put grease in a heatshrink tube, then shrink the tube over the connection/splice. (It helps to use a sheet of waste cardboard or whatever to catch grease squeezed out during shrinking). This is a good compromise between protection and serviceability, since the dielectric grease can be removed later if needed, but provides very good moisture protection.

[VanMarco]

thanks mate. It also appears they wired 2 defrost coils in some way, there is some sort of blue wire that goes all around the drain pipe, i am almost 100% positive it's not stock, as it does not appear on the exploded view. I have put up a schematic of what all that mess look like. The white part i have no idea what it is, looks like a capacitor of sort. Is this defrost "coil" around the drain really necessary?

[helius]

The defrost timer is outside of this, right? Without knowing how the different sensors are placed, I can't hazard a guess to their function. Maybe they are both overheat/PTC elements that become open when the evaporator is sufficiently warmed.

[VanMarco]

I rewired all correctly, with good heatsrhink and silicone grease inside, i am now not sure how to manage defrost, itried 30 min, it seemed a bit excessive, right now, it is set at 15 mins 3 times a day, I dunno if i can get away with 2. the first day of test i left no defrost for 24 hours, and i could tell by the fact that it was struggling to cool that it was frosted, once the 30 min defrost ended, it went back to cool as before. Any idea how much defrost i would need?

[helius]

It depends on the size and design of the evaporator, but standing fridge-freezers I have seen have been sold with options for defrost every 12 or every 24 hours. The defrost cycle lasts about 10 to 15 minutes and the heater burns about 600 watts.

[VanMarco]

The heater is 200 W in that particular freezer

[helius]

If you will not be opening it constantly, then a 15 minute defrost every 12 hours should be sufficient. The more humidity that gets let in to the compartment, the faster it will ice up.

[VanMarco]

Thanks for all the patience!!
I think when the freezer will be empty again maybe i fit one of these https://www.aliexpress.com/item/1005001387229724.html
this is an exact clone of the eliwell 974
it will probably do a better job at defrosting when needed rather than by a time schedule, but i am a strong believer in if it ain't broken don't fix it