I replaced the double heater defrost timer and defrost thermostat in my ge profile tph21pbsbww,it is not fully defrosting.The lower part of the evap coils builds up ice and then cooling stops in the refrigerator section. Is it possible that the heaters can be installed upside down. I noticed the bottom heater does not emit the same amount of heat/light as the top heater.I also noticed that the top heater has more coils per inch in the glass case than the bottom one should that be reversed?