The inner-workings of a refrigerator can be a mixed bag. Some components are fairly easy to service or repair, while others should only be handled by professionals.
Servicing the Limit Switch
The limit switch is found only on frost-free refrigerators and freezers. Its function is to keep the defrost heating element from exceeding certain set temperatures. If a refrigerator has lots of frost in the freezer compartment, the problem may be the limit switch. However, other components -- the evaporator fan, the defrost timer, and the defrost heater -- can cause the same problem. Check these for malfunctions, as detailed below. If these parts are in working condition, the problem is most likely in the limit switch. Don't try to fix the limit switch yourself; call a professional service person for replacement.
Servicing the Thermostat Control
The thermostat control is usually mounted inside the refrigerator. Its visible control knob is turned to regulate the refrigerator/freezer temperature. The workability of this control can be tested in various ways, depending on the problem. To test the thermostat control:
Step 1: If the compressor runs all the time, turn the control knob to the OFF position. If the compressor still runs, unplug the unit, then pull off the control knob and remove the screws holding the thermostat in place. Pull out the thermostat and remove either the red or the blue wire from its terminal. Plug in the unit. If the compressor doesn't run, the thermostat is faulty. Replace it with a new thermostat.
Step 2: If the compressor runs after the wire is removed from its terminal, there is probably a short circuit somewhere in the unit's wiring. In this case, don't try to fix the problem yourself; call a professional service person.
Step 3: If the refrigerator or freezer runs but the box doesn't cool, unplug the unit and remove the thermostat with a screwdriver. Disconnect both wires from the thermostat. Tape the ends of the wires together with electrical tape, and plug in the appliance. If the refrigerator starts and runs normally, the thermostat is faulty. Replace it with a new one of the same type. Connect the new thermostat the same way the old one was connected.
Step 4: If the freezer compartment is normal but the refrigerator box doesn't cool, set the dials that control both compartments to mid-range. Remove these knobs (they're usually friction-fit). Then unscrew the temperature control housing; you'll see an air duct near the control. Replace the knob on the freezer thermostat and turn the control to the OFF position. Open the refrigerator door and look closely at the air duct. If this duct doesn't open wider in about ten minutes, the control is faulty. Replace the control with a new one of the same type. Connect the new control the same way the old one was connected.
Servicing the Evaporator Fan
In some cases, a faulty thermostat may not be the cause of a warm refrigerator or freezer. A warm box may also be caused by a defective fan, a blocked fan, or broken or bent fan blades. If the blades are jammed, try to free them. If they're bent, straighten them with pliers. If this doesn't solve the problem, call a professional service person.
On some refrigerators, the door switch operates the evaporator fan. If the fan seems to be malfunctioning, the door switch could be faulty. Test the switch as detailed in the last page, and replace it if necessary.