Close all doors on the Frigidaire refrigerator. Leaving the doors open might reduce the effectiveness of the defroster. Kneel and listen for a ticking or clicking sound coming from the bottom of the unit. This is an auditory indicator that the refrigerator has entered its automatic defrost mode. The compressor will not run. Instead, heaters will turn on to melt the frost buildup. In some models, you can see the infrared glow in the freezer compartment.
Note the current time, while letting the defrosting procedures continue. Time the full defrosting cycle, though the defrosting timer may have begun minutes before you noticed. Time the bottom-freezer and side-by-side refrigerators for 30 minutes. Time top-freezer refrigerators for 20 minutes. This hands-off troubleshooting step confirms that the timer is functioning to specifications.
Kneel again to hear if the defrost timer has stopped, after the full 20 to 30 minutes. If it has, that means automatic defrosting procedures have concluded and the timer is working to specifications. Your Frigidaire will turn back on and begin cooling.
Contact a service technician, per Frigidaire's suggestion, if the defrost timer appears to have never operated properly.