GE Profile PSF26PGWBB Technical Service Manual

Also see for Profile PSC25PSWSS: Owner's manual and installation Dimensions and installation information

– 36 –The system is designed to run the fan until the freshfood evaporator thermistor reaches 35°F.Once this temperature is reached, the fan continuesto run for an additional 5 minutes. Under normalconditions, the defrost time takes approximately30 minutes. The maximum time the fan runs in lowspeed is 60 minutes. If the evaporator thermistorhas not reached 35°F after 60 minutes, the controlswitches to extended defrost #1.Fresh Food Extended Defrost #1Occasionally there may be excessive frost on theevaporator coil. This can be attributed to numerousdoor openings, extremely high humidity, poordoor gasket seal, etc. If the normal defrost fantime exceeds 60 minutes, the fan switches to highspeed. The control continues to monitor the freshfood evaporator thermistor for 35°F. When 35°F isreached, the fan runs for an additional 5 minutes athigh speed. The fan can run up to an additional 30minutes at high speed, trying to reach 35°F. After 90total minutes of fan time (60 at low speed and 30 athigh speed), if the fresh food evaporator is still below35°F, the control will switch to extended defrost #2.Fresh Food Extended Defrost #2If the fresh food fan has been operating for 90minutes, the main control searches for a fresh foodthermistor temperature above 52°F. If the fresh foodthermistor is above 52°F, the main control boardassumes there is a problem reading the fresh foodevaporator thermistor, ends the defrost cycle, andreturns to normal cooling.If the fresh food thermistor is less than 52°F, themain control board assumes there is refrigerantleaking through the 3-way valve, keeping the freshfood evaporator cold during the defrost processwhile the freezer evaporator is cooling. The maincontrol board shuts off the compressor and runsthe fresh food fan at high speed until 2 conditionsare met: the evaporator thermistor reaches 35°Fand the fresh food thermistor is 2½°F above theset point. As in the other cycles, the fan continuesto run for an additional 5 minutes after the 35°Fevaporator temperature is reached.Fresh Food Forced DefrostIf the main control board senses the fresh foodsection has been cooling for 45 minutes, itimmediately stops the refrigerant flow throughthe fresh food evaporator. The main control boardchanges the position of the 3-way valve if cooling isstill required in the freezer, or turns the compressoroff if the freezer is satisfied. The fresh food fanoperates on high speed until the evaporatorreaches 35°F, plus an additional 5 minutes after theevaporator reaches 35°F.To prevent the refrigerator from going into forceddefrost when first installed or after a power failure,the control will disregard the 45 minute time limit ifthe freezer temperature is above 20°F.Note: If the fresh food evaporator thermistor iseither open or shorted and the 35°F cutoff cannotbe determined, the main control board defaults to afixed defrost cycle of 1 hour at high-speed fan.Freezer Defrost CycleThe freezer evaporator utilizes a defrost heaterto remove frost from the coil. The control boarddetermines the length of time the heater isenergized. It does this by monitoring the freezerevaporator thermistor. Once the temperature ofthe thermistor reaches 75°F, the control cycles thedefrost heater off. A bimetal safety thermostat(L140-30) provides a backup in the event theevaporator thermistor fails. The safety thermostatprevents the temperature from exceeding 140°F.Note:During the freezer defrost cycle, the compressordoes not operate, even if the fresh food sectionis above the set point.When initiating a freezer defrost cycle, there isa 6-second delay from the time the main boardshuts off the power to the compressor and whenthe defrost heater is energized.••