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Parts for Whirlpool W1TXEMMWT00 Refrigerator - AppliancePartsPros.com

See the attachment for the tech sheet.

This type of problem can be difficult to diagnose.
All I can do is give you a few things to check.

How often does the freezer temperature rise?
If it is around every 8 hours it may be a defrost problem.
Force a defrost cycle and the check that the evaporator/freezer fan shuts off during defrost.
If the fan stays on then it is blowing warm air from the defrost cycle into the freezer.
If the fan is off but the defrost is generating too much heat then it mat be the defrost thermostat is not opening.

FYI: The defrost cycle is a fixed time event but the defrost thermostat should open removing power from the defrost heater once the frost/ice has melted off the evaporator coils. The defrost cycle then continues but with the heater off. So if it does not open too much heat is generated and this will raise the freezer temperature.

Does the compressor seem to be cycling correctly?
Or does it try to start several times before finally kicking on.
This could be a compressor or compressor start device problem.

If the compressor cycles OK then it may be a problem with the control thermostat. If when the freezer temperature is high and tapping or moving the cold control knob slightly causes the compressor to come on then I would replace the control thermostat.

It would be a good idea to remove the cover in the freezer so you can inspect the evaporator coils.
They should have a fairly even coating of frost on them.
Be sure to do this test after the compressor has been on for half an hour or so. If you check them during or shortly after a defrost cycle you may end up with the wrong conclusion.
While in there check the defrost thermostat if it is deformed/bulged replace it.