Unplug the Frigidaire freezer or refrigerator. Lift it slightly from the floor on one corner and walk it away from the wall. Pull it away from the wall so you have enough room to pull of the access panel and work between the unit and the wall.
Remove the back access panel with a screwdriver. Locate the defrost heater and timer on the Frigidaire, which is usually located on the bottom near the back of the unit. Use a flashlight to illuminate the inside of the unit.
Pull the wire connectors from the defrost timer with needle-nose pliers. Do not rip or strip the wires. Pull the defrost timer from the Frigidaire unit and discard it. Insert the new defrost timer into the slot and reconnect the wiring. Refer to the defrost timer's instruction manual for wire orientation to ensure proper hook-up.