Here are your parts
Replacement parts for FRIGIDAIRE FFU1464FW0 Frigidaire/freezer | AppliancePartsPros.com

First check it the compressor is running. You can usually hear it also should be warm and vibrating.

If it is not running it could be a control or a compressor start problem.

If it is running, remove the rear cover in the freezer so you can see the evaporator coil.
Is the fan running? If not check that there is 120 volts across it and if there is replace it.

If the coils only have frost in one area then you are probably low on freon. Usually where the freon enters the coils.
This will be an expensive repair as you will need a pro.
Usually it makes more sense to put those dollars towards a new unit.

If the evaporator coils are iced/frosted over to the point that the fan cannot pull air through them you have a defrost problem.
I cannot find the method to force a defrost and believe it is controlled from the temperature control but cannot confirm this as I also cannot find a wiring diagram.
With luck someone else has this info.

So to eliminate the heater and defrost thermostat.
Unplug the unit.
Unplug the defrost heater (Item 14 in Section 3) and measure it. It should be around 20 ohms.
Unplug the defrost thermostat (Item 20 in Section 3) and measure it . It should be 0 ohms when frozen. Note that it opens just above freezing. Also if it id deformed/bulged replace it even if it measures OK.
If both the above are OK I would replace the control (Item 166 In Section 2)