Frigidaire freezer that will not get colder that -5 to -7 C. I replaced thermistor, defrost thermostat and control panel. A repair tech has said the compressor is good. what I am missing?

Many of the frigidaire units had problems with the defrost termination thermostat located in the freezer compartment. (I have repaired many). It is around 12 dollars
It is clipped to a tube located in behind the freezer back panel. take out the
plastic vent and motor, unplug the motor (very carefully to prevent pulling out the
leads) the defrost termination thermostat has two leads and is clipped onto a
tube. The replacement will have heat shrink and wire nuts, but I often use
**** splices under heat shrink tubing to ensure no moisture gets into the connections and a dab of silicone at the ends of the heat shrink. Make sure the "colder" knob
is set in the middle on the vent stack as this will cause problems if set to "colder".
I have only seen one defective defrost timer (incorrectly assembled) which caused the
gear to stick in one position. You can manually rotate the timer to check operation with
a screwdriver in the access hole on the bottom of the temp control panel. (oddly the new timers are of a different make if it has failed). Unplug unit before servicing.

You are correct on your evaluation of the " tech " the # 4 thermistor is bad . This tells the main control board , the temp of the coils , if they need defrosted , when they are thru defrosting . This thermistor is the 1 " long , torpedo looking piece , clipped on the top left of the coils , with 2 white wires going to it . Part number WR55X10025 . It would be advisable to also replace the # 5 thermistor , located at the bottom of the freezer , slightly in front of the drain , also with 2 white wires going to it , slid into a housing . This thermistor , is the freezer thermistor , which tells the control board , the freezer temp and when to cycle off due to selected temperature .

The timer is the main control board behind the refrig , behind the 8X10 panel . If you have a defrost problem , Pull the refrig out and remove the 8 " x 10 " panel . Behind this panel , is the main control board . Unplug the refrig . Remove the BLUE plug from the board , with 3 larger wires going to it . Looking at the blue plug , the sequence will be wire1,wire2,space,wire3 . Get a short piece of insulated wire , and strip about 1/4 inch from each end . Insert 1 end into wire2 , and the other into wire3 . Plug the refrig back in . After about 3 min , look in the freezer , at the bottom , behind the crisper , look for a red glow . If no red glow , unplug the refrig , and reassemble the plug and cover . This no glow , indicates a shorted defrost heater . It is also advisable to replace the defrost thermostat ( pt. number WR50X10068 ) when replacing the heater . To access these parts , you will have to remove the inside rear wall of the freezer . The heater , is at the bottom of the coils , held on with 2 screws , and the thermostat , is the 1 " cylinder , with a blue and pink wire going to it , clipped on the top left of the coils .
If you do get a red glow , then the # 4 thermistor is bad . This tells the main control board , the temp of the coils , if they need defrosted , when they are thru defrosting . This thermistor is the 1 " long , torpedo looking piece , clipped on the top left of the coils , with 2 white wires going to it . Part number WR55X10025 . It would be advisable to also replace the # 5 thermistor , located at the bottom of the freezer , slightly in front of the drain , also with 2 white wires going to it , slid into a housing . This thermistor , is the freezer thermistor , which tells the control board , the freezer temp and when to cycle off due to selected temperature .

I have never found a control board causing a defrost problem .

Pull the refrig out and remove the 8 " x 10 " panel . Behind this panel , is the main control board . Unplug the refrig . Remove the BLUE plug from the board , with 3 larger wires going to it . Looking at the blue plug , the sequence will be wire1,wire2,space,wire3 . Get a short piece of insulated wire , and strip about 1/4 inch from each end . Insert 1 end into wire2 , and the other into wire3 . Plug the refrig back in . After about 3 min , look in the freezer , at the bottom , behind the crisper , look for a red glow . If no red glow , unplug the refrig , and reassemble the plug and cover . This no glow , indicates a shorted defrost heater WR51X10101 . It is also advisable to replace the defrost thermostat ( pt. number WR50X10068 ) when replacing the heater . To access these parts , you will have to remove the inside rear wall of the freezer . The heater , is at the bottom of the coils , held on with 2 screws , and the thermostat , is the 1 " cylinder , with a blue and pink wire going to it , clipped on the top left of the coils .
If you do get a red glow , then the # 4 thermistor is bad . This tells the main control board , the temp of the coils , if they need defrosted , when they are thru defrosting . This thermistor is the 1 " long , torpedo looking piece , clipped on the top left of the coils , with 2 white wires going to it . Part number WR55X10025 . It would be advisable to also replace the # 5 thermistor , located at the bottom of the freezer , slightly in front of the drain , also with 2 white wires going to it , slid into a housing . This thermistor , is the freezer thermistor , which tells the control board , the freezer temp and when to cycle off at selected temp .

Pull the refrig out and remove the 8 " x 10 " panel . Behind this panel , is the main control board ( you already know , since you changed it ) . Unplug the refrig . Remove the BLUE plug from the board , with 3 larger wires going to it . Looking at the blue plug , the sequence will be wire1,wire2,space,wire3 . Get a short piece of insulated wire , and strip about 1/4 inch from each end . Insert 1 end into wire2 , and the other into wire3 . Plug the refrig back in . After about 3 min , look in the freezer , at the bottom , behind the crisper , look for a red glow . If no red glow , unplug the refrig , and reassemble the plug and cover . This no glow , indicates a shorted defrost heater ( pt. number WR51X10055 ) . It is also advisable to replace the defrost thermostat ( pt. number WR50X10068 ) when replacing the heater . To access these parts , you will have to remove the inside rear wall of the freezer . The heater , is at the bottom of the coils , held on with 2 screws , and the thermostat , is the 1 " cylinder , with a blue and pink wire going to it , clipped on the top left of the coils .
If you do get a red glow , then the # 4 thermistor is bad . This tells the main control board , the temp of the coils , if they need defrosted , when they are thru defrosting . This thermistor is the 1 " long , torpedo looking piece , clipped on the top left of the coils , with 2 white wires going to it . Part number WR55X10025 . It would be advisable to also replace the # 5 thermistor , located at the bottom of the freezer , slightly in front of the drain , also with 2 white wires going to it , slid into a housing . This thermistor , is the freezer thermistor , which tells the control board , the freezer temp , when to cycle off , associated with the fan speed also .

Pull the refrig out and remove the 8 " x 10 " panel . Behind this panel , is the main control board .. Unplug the refrig . Remove the BLUE plug from the board , with 3 larger wires going to it . Looking at the blue plug , the sequence will be wire1,wire2,space,wire3 . Get a short piece of insulated wire , and strip about 1/4 inch from each end . Insert 1 end into wire2 , and the other into wire3 . Plug the refrig back in . After about 3 min , look in the freezer , at the bottom , behind the crisper , look for a red glow . If no red glow , unplug the refrig , and reassemble the plug and cover . This no glow , indicates a shorted defrost heater WR51X10055 . It is also advisable to replace the defrost thermostat ( pt. number WR50X10068 ) when replacing the heater . To access these parts , you will have to remove the inside rear wall of the freezer . The heater , is at the bottom of the coils , held on with 2 screws , and the thermostat , is the 1 " cylinder , with a blue and pink wire going to it , clipped on the top left of the coils .
If you do get a red glow , then the # 4 thermistor is bad . This tells the main control board , the temp of the coils , if they need defrosted , when they are thru defrosting . This thermistor is the 1 " long , torpedo looking piece , clipped on the top left of the coils , with 2 white wires going to it . Part number WR55X10025 . It would be advisable to also replace the # 5 thermistor , located at the bottom of the freezer , slightly in front of the drain , also with 2 white wires going to it , slid into a housing . This thermistor , is the freezer thermistor , which tells the control board , the freezer temp , when to cycle off , associated with the fan speed also .

It sounds like the # 4 thermistor is bad . You will have to remove the lower inside rear freezer panel ( 2 or 4 screws ) and on the top of the coils , you will see a 1 " long torpedo looking piece , clipped on , with 2 white wires going to it . Part number WR55X10025 . This thermistor , tells the maon control board , the temperature of the freezer coils ( evaporator ) and when to defrost and when to stop defrosting and turn the compressor back on . There is also a defrost thermostat which cuts the heater off to keep from over heating , but I do not believe this is part of your problem . You should also replace the # 5 thermistor , located behind the oval grill , mounted on the lower right side of the freezer . This thermistor , tells the main control board , the temperature of the freezer section .

Sounds like defrost timer is not putting the refrigerator in defrost every 8 hours. You freezer should be below -5 degrees. Also the condenser beneath the refrigerator possibly needs cleaning. First slowly turn the defrost timer clockwise until freezer goes in defrost. You should hear the sound of crackling noise in freezer after about one minute into defrost. If timer does not come out of defrost or does not turn itself then replace it. Let me know what you find, Thanks Sea Breeze

Sounds like a defrost problem or a plugged drain... to get it to work temporary defrost the freezer. Unplug the refrigerator, open the door and get a blow dryer and warm up the freezer. wait until the water stop dripping out or about 12 to 24 hours and then you can plug it back in . it will work for 2 to 3 weeks.

To unplug the drain.defrost the freezer .remove the back cover. Use a pipe cleaner to clear the drain. pour a few cups of hot water down the drain.

The defrost systems is:
HEATER-DEFROST
THERMOSTAT-DEFROST
Adaptive defrost control
Start with the adaptive defrost control board. The fresh food section light switch and light bulb must work. To initiate a defrost cycle, open the door and push the light switch in and out 5 times within 6 seconds. The compressor and fans should shut off and the defrost heater should come on. Open the door and push the light switch in and out 5 times within 6 seconds to remove the refrigerator from the defrost mode and back into a cooling mode.
Frigidaire - referance model FSC23F7DSB3
This product comes equipped with an Adaptive Defrost Control (ADC). To activate manual defrost, press and hold the Freezer temperature UP (WARMER) key while pressing the Fresh Food temperature DOWN (COLDER) key 5 times within 6 seconds. A �d� in the freezer temperature window and �F� in the refrigerator temperature window will display when the heater is activated. To deactivate manual defrost, press and hold Freezer temperature UP (WARMER) key while pressing the Fresh Food temperature DOWN (COLDER) key 5 times within 6 seconds. �d� and �F� will be displayed until the defrost cycle is complete. (approx. 8 minutes)

Heater / Thermostat
You will have to remove the back panel of the freezer to check the heater for and thermostat for continuity. Heater are the lease likely part to go bad... I always change thermostat and timers together.
let me know if this helps or we can chat if you need more help.

Sounds like a defrost problem or a plugged drain... to get it to work temporary defrost the freezer. Unplug the refrigerator, open the door and get a blow dryer and warm up the freezer. wait until the water stop dripping out or about 12 to 24 hours and then you can plug it back in . it will work for 2 to 3 weeks.

To unplug the drain.defrost the freezer .remove the back cover. Use a pipe cleaner to clear the drain. pour a few cups of hot water down the drain.

The defrost systems is:
HEATER-DEFROST
THERMOSTAT-DEFROST
Adaptive defrost control
Start with the adaptive defrost control board. The fresh food section light switch and light bulb must work. To initiate a defrost cycle, open the door and push the light switch in and out 5 times within 6 seconds. The compressor and fans should shut off and the defrost heater should come on. Open the door and push the light switch in and out 5 times within 6 seconds to remove the refrigerator from the defrost mode and back into a cooling mode.
Frigidaire - referance model FSC23F7DSB3
This product comes equipped with an Adaptive Defrost Control (ADC). To activate manual defrost, press and hold the Freezer temperature UP (WARMER) key while pressing the Fresh Food temperature DOWN (COLDER) key 5 times within 6 seconds. A �d� in the freezer temperature window and �F� in the refrigerator temperature window will display when the heater is activated. To deactivate manual defrost, press and hold Freezer temperature UP (WARMER) key while pressing the Fresh Food temperature DOWN (COLDER) key 5 times within 6 seconds. �d� and �F� will be displayed until the defrost cycle is complete. (approx. 8 minutes)

Heater / Thermostat
You will have to remove the back panel of the freezer to check the heater for and thermostat for continuity. Heater are the lease likely part to go bad... I always change thermostat and timers together.
let me know if this helps or we can chat if you need more help.