Refrigerator Thermostat not working FIX

Refrigerator thermostat is one of the main components inside the refrigerator . Thermostat is the component that allows the user to set the refrigerator temperature . This is basically a switch that turns off at a set temperature.  However , these thermostats can eventually go bad . Bad thermostats can cause non functioning  cooling system or always on cooling system .(which can cause refrigerator Ice buildup ) In this tutorial lets look into what cause the refrigerator thermostat not working and how to fix it.

Purpose of a Thermostat

Thermostat Inside - Thermostat Not working Fix

Thermostat Inside

As we have mentioned earlier Thermostat is a switch that breaks the power supply to the cooling system. Thus , preventing over cooling . It switches the compressor and the fan . The main purpose is to allow the user to set the desired temperature inside the refrigerator. The thermostat also have some role in prevention of ice building up inside the refrigerator freezer compartment. Even if you set  the thermostat to it’s maximum value the thermostat not going to cause the cooling system to work all the time. Because , The maximum value you can set in the thermostat is decided by the engineers to prevent any over cooling that may cause ice build up that cannot be cope-with the defrost circle.

Working Principle of a Thermostat

Thermostat Inside parts

Thermostat Inside parts

There are mainly two mechanical thermostat types the bi-metal thermostat and capillary tube thermostat . Most common type of thermostat that used in refrigerator is the capillary tube thermostat . Capillary tube thermostat consist of three main parts The Capillary tube system , Mechanical Relay and Mechanical adjusting system.



The Capillary tube system

Thermostat Capillary Tubing and Bellow - Thermostat Not working Fix

Thermostat Capillary Tubing and Bellow

It’s a long metal tubing with hole inside .In one end there is a sensing bulb and at the other end is the The capillary bellow (diaphragm) .This tubing is a hollow tubing and it’s confined system filled with freon gas . One side of the tube is crimped (Sensing bulb side) and the other side is open to the bellow . As the tubing exposed to the cold temperature the gas contracts .Causing , bellow to contract .The bellow is pushed by a mechanical system connected to the relay .As the bellow contracts the mechanical components that pushes the bellows also moves towards it. At one point this mechanical system will trigger the relay  opening the contacts .Thus , Breaking the circuit (Open circuit).

Mechanical Relay

Thermostat Inside Relay - Thermostat Not working Fix

Thermostat Inside Relay

Mechanical relay is a relay that trigger using mechanical means  .The mechanical relay of a thermostat is situated under the thermostat .The contraction of bellow cause the plate that pushes the bellow to move up ward .This upward action release the pressure that put on the relay causing the contacts to be opened . Once the temperature inside freezer increases the bellow will expand pushing the plate other side .This forward action of the plate will put the pressure on the relay causing the relay to make contact .

Mechanical Adjustment system

Thermostat Inside Adjustment system

Thermostat Inside Adjustment system

This system consist of one main dial and hidden adjuster.The main dial rod is fitted with the knob that user can rotate and set temperature. The hidden adjuster is a screw adjuster that set the tension of the spring that pushes the plate towards the bellow .If you rotate the screw adjuster anti-clockwise you can increase the tension of the spring .Thus , Increasing the value of the main dial can reach (Setting the maximum). If you rotate the screw clockwise you can reduce the tension of the spring .Resulting , lowering of the value of the main dial can reach .This same assembly is used for for pushing the relay trigger .

Refrigerator Thermostat Not working Fix

There are are several things that can cause defrost timer malfunction . However ,These things can be fixed easily .Here are some of the causes of refrigerator thermostat not working and how to fix them.


Checking refrigerator heater

Checking the motor coil

Rust is very common cause where metal and moisture present .There are many moving metal parts inside a thermostat . Rusting can cause stuck and broken parts which will cause the malfunction of the thermostat regulator .

fix – If you can see any rust use a sand paper or wire brush to remove the rust and If there any damaged parts due to rust . Try to replace the part .Then , Apply some grease on the moving mechanical parts.

Damaged Capillary System

Simple puncher  in the capillary tubing and bellow can cause the refrigerant gas to be relisted to outside. That’s why you should be careful when handling the capillary tubing . It can lost it’s seal anytime specially at the place where capillary tube and bellow connects .

Testing – you can test if the capillary system is good or bad by measuring the movement of the bellow .You don’t have to take apart the thermostat. Look at the top of the thermostat you will see a metal part (dial) inside a rectangular shaped cutout. It moves as the bellow contracts and expands.Look at the position of that dial at room temperature .Then , Put the capillary tube inside a glass filled with ice cubes . See whether the dial moves or not (results may take some time ) . If you cant see any movement in the dial you have either bad capillary system or a mechanical problem

Fix – If the capillary tubing goes bad there is little or less you can do .It require special equipment to fill and fix the puncher .

Bad relay Contacts

Sanding contact points - defrost timer not working fix

Sanding contact points of defrost timer

As the relay trigger pushes and retracts the contacts made and breaks. As the contacts touches each other sparks can appear these sparks appear due to the current flow through two contact points . These sparks can cause the contact points to be damaged. If contact points are damaged and deformed the contacts are not properly made .Thus, No current flow. This is one of the main causes of refrigerator thermostat not working.

Fix – Use a fine sand paper (600P -1000P) and sand it down to it’s proper shape to make sure proper contacts made between each contact points .


cleaning refrigerator connector pins

Cleaning oxidized metal parts

If you are living in a coastal area ,you know that oxidization is a big problem in day-today life. These oxidization can effect any metal part inside the defrost timer .

Fix – Take apart the defrost timer. Use a toothbrush dipped in a isopropyl alcohol . Then , Brush any metal part inside. You can also use a contact cleaner and spray to the metal contacts inside the defrost timer.


In conclusion

Capillary tube thermostats can go bad due to various reasons. Mechanical thermostats can be easily repaired .In the otherhand electronic thermostats . Although , some repairs require special tools most repairs doesn’t require such knowledge or tools. You should be careful when handling capillary tube .It can be easily damaged .

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