Jean F Monroe Township , NJ September 05, 2016 Appliance: Frigidaire Refrigerator PHT219HSM5 Frigidaire Refrigerator Pht219hsm5: Defrost cycle was not working thus ice build up on evaporator coils was blocking vent to refrigerator compartment which was not getting cool freezer section seemed to be fine. How to replace Defrost Timer. Replaced defrost timer, defrost thermostat, and defrost heater. I didn't have a continuity meter to check old parts so replaced all three. Also cleaned condenser coils. Used your videos to help with repair. 1 People found this story helpful Do-It-Yourself Rating: Repair Time Estimate: 1-2 hours