501f freezer ices up the evaporator. After defrosting it works well until it ices up again.

It appears that your auto defrosting system (if you have one) is not working. So your evaporator coil is frozen up - all that ice serves as an insulator and not enough cold air is getting down into frig section. Until you replace either the freezer defrost element or the defrost timer all you need to do is unplug for a few hours till it fully defrosts then plug back in - will work fine for a few days at normal internal temps till the ice builds up again.

If your timer and defrost element are both working properly, THEN, you might want to check if you have enough refrigerant in the system - you may have a leak.

Melt the iced up evaporator with a hairdryer for a temp. fix. The auto defrost system isn't working. I can't find diagrams of yours but here is basically how it works.

The evaporator coil behind the cover on the back wall inside the freezer will ice up under normal conditions. Every 8 to 10 hours for around 20 minutes the defrost timer (or in most newer models the electronic adaptive defrost control) will turn the defrost heater on to melt the built up ice. There is a defrost thermostat which prevents the heater from overheating the freezer by breaking the heater circuit when the temp reaches close to 32 degrees F. The entire cooling system shuts off during the defrost cycle and starts back when the timer advances through the cycle.

If this ice is not melted it will continue to build up until the air can't flow over the coil to circulate the cold air through the freezer and into the fridge. The temperature change in the fridge is usually noticed first followed by the freezer.

If the defrost thermostat is bad, it can prevent the heater from coming on OR it won't turn the heater off when it gets too warm. It is clamped to the evaporator coil at the top to sense the temp. If it appears to be misshapen it is bad.
With an ohm meter it should show continuity when cold and none when warm.
You can also bypass(disconnect the two wires plugged into it and twist them together) the thermostat to see if the heater comes on then. If it does then you know the thermostat is bad and needs replaced.

The defrost heater is located on the evaporator. It is in a tube which is at the bottom and can also go up the sides of the evaporator. On some types you can see a burnt spot if it's bad. With an ohm meter it should show continuity from end to end when disconnected from the wiring in the freezer. You can also test the wiring for voltage when it's in the defrost mode.

If you have a defrost timer you can test it. It can be located under the fridge behind the kick panel on the front. Some are in the fridge with the controls at the top. You can turn the defrost timer till it clicks and everything shuts down. The heater should now come on. If it does, replace the timer because that means the timer is not running. If it doesn't, check the heater and defrost thermostat. Turn the timer again till everything starts back up to end the defrost cycle.

If you have an adaptive defrost control instead of a timer, replace it if the heater and thermostat test good. It is located in the fridge with the controls in some models and on the back in others.

bad defrost element or timer

DEFROST PROBLEM The evaporator coil behind the cover on the back wall inside the freezer will ice up under normal conditions. Every 8 to 10 hours for around 20 minutes the defrost timer (or in most newer models the electronic adaptive defrost control) will turn the defrost heater on to melt the built up ice. There is a defrost thermostat which prevents the heater from overheating the freezer by breaking the heater circuit when the temp reaches close to 32 degrees F. The entire cooling system shuts off during the defrost cycle and starts back when the timer advances through the cycle.
If this ice is not melted it will continue to build up until the air can’t flow over the coil to circulate the cold air through the freezer and into the fridge. The temperature change in the fridge is usually noticed first followed by the freezer.
If the defrost thermostat is bad, it can prevent the heater from coming on OR it won’t turn the heater off when it gets too warm. It is clamped to the evaporator coil at the top to sense the temp. If it appears to be misshapen it is bad. With an ohm meter it should show continuity when cold and none when warm. You can also bypass(disconnect the two wires plugged into it and twist them together) the thermostat to see if the heater comes on then. If it does then you know the thermostat is bad and needs replaced.
The defrost heater is located on the evaporator. It is in a tube which is at the bottom and can also go up the sides of the evaporator. On some types you can see a burnt spot if it’s bad. With an ohm meter it should show continuity from end to end when disconnected from the wiring in the freezer. You can also test the wiring for voltage when it’s in the defrost mode.
If you have a defrost timer you can test it. It can be located under the fridge behind the kick panel on the front. Some are in the fridge with the controls at the top. You can turn the defrost timer till it clicks and everything shuts down. The heater should now come on. If it does, replace the timer because that means the timer is not running. If it doesn't, check the heater and defrost thermostat. Turn the timer again till everything starts back up to end the defrost cycle.
If you have an adaptive defrost control instead of a timer, replace it if the heater and thermostat test good. It is located in the fridge with the controls in some models and on the back in others.

If the evaporator coils behind the back panel of the freezer are icing up because of auto defrost failure that will stop the circulation of cold air and eventually affect the freezer too.
The evaporator coil behind the cover on the back wall inside the freezer will ice up under normal conditions. Every 8 to 10 hours for around 20 minutes the defrost timer (or in most newer models the electronic adaptive defrost control) will turn the defrost heater on to melt the built up ice. There is a defrost thermostat which prevents the heater from overheating the freezer by breaking the heater circuit when the temp reaches close to 32 degrees F. The entire cooling system shuts off during the defrost cycle and starts back when the timer advances through the cycle.

If this ice is not melted it will continue to build up until the air can’t flow over the coil to circulate the cold air through the freezer and into the fridge. The temperature change in the fridge is usually noticed first followed by the freezer.

If the defrost thermostat is bad it can prevent the heater from coming on OR it won’t turn the heater off when it gets too warm. It is clamped to the evaporator coil at the top to sense the temp. If it appears to be misshapen it is bad.
With an ohm meter it should show continuity when cold and none when warm.
You can also bypass the thermostat to see if the heater comes on then. If it does then you know the thermostat is bad and needs replaced.

The defrost heater is located on the evaporator. It is in a tube which is at the bottom and can also go up the sides of the evaporator. On some types you can see a burnt spot if it’s bad. With an ohm meter it should show continuity from end to end when disconnected from the wiring in the freezer. You can also test the wiring for voltage when it’s in the defrost mode.

If you have a defrost timer you can test it. It can be located under the fridge behind the kick panel on the front. Some are in the fridge with the controls at the top. You can turn the defrost timer till it clicks and everything shuts down. The heater should now come on. If it does, replace the timer because that means the timer is not running. If it doesn't, check the heater and defrost thermostat. Turn the timer again till everything starts back up to end the defrost cycle.

If you have an adaptive defrost control instead of a timer, replace it if the heater and thermostat test good. It is located in the fridge with the controls in some models and on the back in others.

It can be one of three things. Unplug and use an Ohm Meter to measure the resistance of the defrost heater that is mounted on the evaporator coil in the freezer compartment. Then disconnect the defrost heater and measure with ohm meter. It should measure in the 20 ohm range. If it measures as "open" replace the coil.

Next suspect is the defrost timer mounted in the front of the compressor compartment. It's tough to test, so I'd just replace the timer.

Finally, there is a sensor mounted on the top of the defrost heater that shuts off the defrost heater when it reaches a high temperature. If the coil tests OK, and you are going to replace the timer, you may want to replace the sensor too.
It is awkward to test, the temperature of the sensor needs to be be below room temperature to close. The cost of the sensor is low enough that you may not want to replace the timer, then test the system, and then have to go back in to replace the sensor later.

Check defrost heater that goes into drain tube. When the drain freezes ;the defrost water spills into the icemaker.

Check the condenser fan underneath the unit accessable form the back behind the cardboard cover. It should be running when the compressor runs. OR Check the evaporator behind the rear cover inside the freezer. Check for ice build up. . Light frost everywhere(NORMAL) or a partial pattern of ice(LOW ON FREON) or nothing(LOW FREON OR COMPRESSOR PROBLEM).
If the evaporator coils behind the back panel of the freezer are icing up because of auto defrost failure that will stop the circulation of cold air and eventually affect the freezer too.

check defrost timer, defrost heater, defrost thermostat. In most newer models the timer has been replaced by an electronic control board. If the heater and thermostat are ok it’ll be the control

Make it a habit to defrost it every week. You see, when ice forms around the evaporator tubes (which runs around the walls of fridge and freezer), heat exchange reduces (that means heat is no longer absorbed from the things inside the refrigerator) and cooling stops. See whether freezer walls or fridge walls are damaged. Do not use knives or any other sharp tools to remove ice. Do not forcefully remove items that are difficult to take out from the freezer. Defrost and remove them.

If its a frost free upright freezer and the evaporator is frosting up with a snow like frost you have a defrost problem.. defrost themostate, heaters, or timmmer