Why is my freezer not freezing?

Hi,

You said that “I checked the temperature sensor with the ohm meter, and it seems OK, ….”. Just curious whether it was it showing the correct resistance for the temperature indicated or not?

Here’s a composite image taken from the service manual and the 502AT thermistor datasheet showing the resistance value for the thermistor at the various temperatures.

(click on image to enlarge for better viewing)

Did it go into forced operation and signal that it did after you left it overnight? (see p.66 or 67 of the service manual)

Hi,

Can’t see it to well from your image but did you measure the sensor out of circuit i.e. disconnected from where it plugs into the connector at the back and measured directly across the sensor wires themselves, not at the plug point still plugged in? Hopefully this makes sense ;-)

The reason is that as can be seen from the wiring diagram (see below) the sensor is in parallel with some other sensors and if measured with it still connected the reading on the meter wouldn’t be accurate.

If you didn’t measure it when disconnected, unplug the sensor and measure directly across the two sensor wires at their plug and not at the socket that it plugs into. That way you are looking only at the sensor with the meter. Try not to touch the sensor itself with your fingers as this will start to warm the sensor and alter the reading.

If you did measure it out of circuit and the reading was 7.5 Ohms then this indicates a temp of appprox. 15C

(click on image to enlarge for better viewing)

The fact that the sensors are all connected would be taken into account when the circuit was designed so as to give an accurate display but would still rely on the fact that the sensor has to give the correct resistance reading at the specified temperatures whether it was connected as it is or as a standalone sensor.

Hi @katkacyt,

One thing that may have been overlooked as I couldn’t see it mentioned in the question/comments etc.

Is the evaporator fan in the freezer operating? The door may have to be closed for it to operate as usually evap fans are turned off when a door is opened to prevent the cold air from being blown out the door. It falls out fast enough as it is ;-)

If a door switch is visible in the door jamb and is not a hidden magnetic switch in the frame then with the door open you should be able to manually operate the switch to start the fan again. The lights should also turn off when the switch is operated. If there is no visible door switch then you may have to mark a blade of the fan with a marker pen etc, and then close the door and open it again about 5-10 seconds later and check if the blade has changed position indicating that the fan has operated. The fan should be operating as long as the compressor is operating.

Only suggest this as you said that frost is forming on the coils and this won’t occur if the temp is above 0 C. so the temp in the evap unit is <0 C and this is not being distributed throughout the freezer.

The caveat with all this is that there are two fans in the refrigerator for cooling purposes, one in the freezer compartment and one in the refrigerator compartment, so the freezer fan may be stopped while the compressor is running IF the control board thinks that the freezer is cold enough but not the refrigerator.

If the fan doesn’t operate at all here’s an image of the operate circuit from the control board. Disconnect the power from the fridge and then disconnect the cable on the board and test between pins 4 & 8 on the cable and also between pin 7 and the fan motor itself, should be a red wire on the fan. I don’t know what the resistance between 4 & 8 will be but it won’t be open circuit. I think that the red wire may be the fan sensor wire but I may be wrong. Anyway there should be a connection from the board to the fan on all 3 wires, and the fan motor should be between 2 of the 3 wires

(click on image to enlarge for better viewing)

The above is just trying to eliminate another possibility, so if the freezer evap fan is OK and since you have checked the freezer temperature thermistor circuit back to the control board and it is OK, that only leaves the control board OR perhaps a sealed system problem i.e. a compressor problem or a lack of refrigerant due to a leak. Low refrigerant levels can mean that the refrigerator gets cold enough but not the freezer. Check for any oily residues on the condenser coils or under the compressor. There is a special lubricating oil mixed in with the refrigerant to help lubricate the compressor. If there is a leak anywhere, the refrigerant will escape to the air undetected but the oil will leave a trace.

You can either replace the control board (find a supplier with a good returns policy if it turns out not to be the board) and if it isn’t the board then the high/low pressures in the sealed system will need to be checked. Depending on your location, this most probably will have to be done by a licensed refrigerator repairer, due to the regulations regarding the handling of refrigerant gases that apply in a lot of places.