What is the make and model number of the freezer?
Do you mean that the temp goes from -22 to 2 and then back to -22 centigrade again?
How often does this happen?
If only once every 8-10 hours it may just be the defrost cycle in operation
The defrost cycle takes about 15-25 minutes and during this time the compressor and evaporator fan are both stopped i.e. cooling is stopped and temp rises in compartment and the defrost heater is turned on to melt the ice build up on the evaporator unit. The temp will rise from -22 to 2. Really it should not rise above 0 C as you don’t want the frozen food to even begin to thaw.
When the set temp of the defrost thermostat (or sensor) has been reached i.e. 0 deg., it signals the control board to end the defrost cycle by turning off the heater and to restart the compressor and the evaporator fan again to drive the temp back down again to the set temperature. e.g. -22deg.
-22 C is a bit cold so it may be a faulty temp sensor in the freezer. The same with the defrost sensor as it shouldn’t really go above 0 deg C.
Have you tried using a thermometer to check the temperature in the freezer if the temperatures you’re seeing are shown on a control panel, just in case there is an error in the display reading?
Check if the temperature sensor is OK. The sensor appears to be a NTC type thermistor (Negative Temperature Co-efficient) which means that as the temperature goes up the electrical resistance value of the thermistor goes down. The resistance value of a thermistor over its designed operating temperature range is known so this is how the control board knows what the temperature is at any given temperature as the thermistor’s resistance will indicate this.
Here’s an image showing the resistance chart for 6 different thermistor models. It is only to show you how its resistance changes with the temperature. The resistance values are in K Ohms i.e Ohms x 1000. As far as I know they are not the ones used in your freezer, but I may be wrong. Check if the one in your freezer has any model or type information printed on it. You may be able to find the specifications for it by searching online for the number so that you can check if it is OK or not at the given temperature.
(click on image to enlarge for better viewing)
Unfortunately its location is not shown in the parts diagrams as it is shown as NI (not indicated) in the system diagram parts list.
Also according to the same parts supplier linked above the part number for the service data sheet is 297079601.
It shows that the temperature should be between -13C to -16C when the room ambient is between 21C to 32C. at Setting #1. (approximate Celsius temperature values converted from the Fahrenheit temps shown on data sheet)
Other than this it doesn’t give much more information apart from a very basic block diagram of the freezer components and how they’re connected with each other. The thermistor (aka temperature sensor) is also shown, along with a 9V battery??, connected to the control board.
I’ve never come across a battery in a refrigerator (or freezer) before but I was wondering if it is used to maintain the settings in the event of a power failure.
I know that this is the case in computers and when the battery gets low (or flat) it can cause all sorts of strange things to happen. So it may be worthwhile also checking it to see what voltage it is or still is. I don’t know whether it is a rechargeable or a non rechargeable but in either case they have a lifespan. Just a thought.