How does a thermo switch work?

Asked By: Abel Ebelt | Last Updated: 18th June, 2020
Category: home and garden indoor environmental quality
4.4/5 (694 Views . 32 Votes)
A thermal switch is an electromechanical device which opens and closes contacts to control the flow of electrical current in response to temperature change. It cuts off the current to critical machinery when a temperature limit is exceeded preventing potential burn out or failure.

Click to see full answer


In respect to this, what is a thermo switch?

A coolant fan switch is a small and very simple switch comprised of typically two wires. This switch is configured to work based upon the temperature of the engine. As engine temperature rises to a specific threshold, the switch is activated powering on the coolant fan.

Beside above, what are the signs of a bad temperature sensor? Common symptoms of a bad engine coolant sensors are overheating, hard starting conditions, poor idle, check engine light ON and the electric fans do not work properly. The easiest way is to read the trouble code memory and check the value from the sensor, to make sure it's a possible value.

Also to know is, why does my radiator fan not turn on?

A fan failure, or a failure of the fan relay or control circuit is bad news because it can allow the engine to overheat. Engine thermostat is stuck OPEN (engine never gets hot enough to turn on the fan) Faulty fan relay. A wiring problem (blown fuse, loose or corroded connector, shorts, opens, etc.)

What are the symptoms of a bad temperature sensor?

Symptoms of a bad or failing coolant temperature switch (sensor)

  • Poor fuel economy. One of the first symptoms associated with a problem with the coolant temperature sensor is poor fuel economy.
  • Black smoke from engine. Another symptom of a possible problem with the coolant temperature sensor is black smoke from the vehicle's exhaust.
  • Overheating engine.
  • Check Engine Light comes on.

38 Related Question Answers Found

How does a radiator fan relay work?

The function of the cooling fan relay is to convert a low voltage signal from either the electronic control module (ECM) or a thermostatically controlled sensor. The cooling fan relay takes the low voltage signal and internally switches the relay “on” to allow battery voltage to be supplied to the radiator cooling fan.

Does thermostat control radiator fan?

The thermostat in the cooling system controls many of the electric fans. When the temperature in the engine reaches a certain preset temperature, the fan will begin cooling the engine. When the temperature dips below that preset temperature, the fan will turn off.

Where is the fan switch?

The electric cooling fan switch is installed into a coolant passage of the engine near the thermostat housing and operates the radiator electric cooling fans when the coolant temperature reaches a specified temperature.

What is a thermo unit?


The Model 3605-A Thermo Unit by King Nutronics Corporation is a self-contained portable dry well temperature calibration system based on a Peltier element, which permits the generation and control of temperatures from –40°F to 250°F, with an unsurpassed accuracy of ±0.5°F throughout its operating range.

What is the sensor on the radiator?

A coolant temperature sensor (CTS) (also known as an ECT sensor or ECTS (engine coolant temperature sensor) is used to measure the temperature of the coolant/antifreeze mix in the cooling system, giving an indication of how much heat the engine is giving off.

How do you know if your car thermostat is working?

Start your car's engine and allow it to idle. Look through the radiator filler neck to see if the coolant flows. At this time, it should not be flowing as your car has not reached the operating temperature to cause the thermostat to open. If you find the coolant is flowing, it means the thermostat valve is open.

How do you check a relay?

Listen for a click when the relay is energized. Check the energized condition of the relay contacts. Use a digital multimeter (DMM) to test the resistance between each pole of the relay and the corresponding NC and NO contacts for that pole. All NC contacts should read infinite resistance to the corresponding pole.

Where is the temperature switch on a car?

On most vehicles, the coolant temperature sensor (CTS) can be found somewhere near the engine thermostat, which allows it to function optimally. The tip of the CTS is probably located right next to the engine coolant.

How can you tell if a fan relay is bad?


Symptoms of a Bad or Failing Cooling Fan Relay
  1. Engine running hot. One of the first symptoms commonly associated with a bad or failing cooling fan relay is an engine that runs hot or overheats.
  2. Cooling fans do not function. Non-functional cooling fans are another common symptom of a potential problem with the cooling fan relay.
  3. Cooling fans stay on at all times.

Why is my Kawasaki Mule overheating?

Air trapped in the system will usually make it's way to the water pump. The water pump does a good job of pumping coolant, but it won't pump air. Thus the radiator stays cold or cool and the engine overheats. That's why the system has to be bled.

Why does my cooling fan stay on all the time?

If the cooling fans are staying on at all times, this is another (less common) symptom of a possible problem with the cooling fan relay. The cooling fan relay essentially functions as the switch for the engine's cooling fans, and is therefore an important electrical component of the vehicle's cooling system.

What temperature should thermo fans come on?

Re: Thermo fans and engine temps
Use a 72 degree thermostat (TRD ones are 72 degrees but prohibitively expensive - suggest the Tridon catalogue). Set the fan to come on at 75 or 80.

Should both fans be on when AC is on?

Both radiator fans should always run when the AC compressor is engaged. Both radiator fans should always run when the coolant temperature sensor in the bottom tank of the radiator reaches about 212*F.

Do I need a relay for electric fan?


You need to use a relay on any high draw component..Especially Fan motors, and TWO in parallel are preferred as a Safety Issue. A Relay Coil (Or Set of coils) Will only draw an amp to an amp in a half, Whereas The motor will draw 17 amps and Spike on startup, or If you Suffer a rotor lock on the motor..

How much is a cooling fan relay?

So, when the cooling fan relay stops working, the coolant can get too hot, and the car can overheat. To get your cooling fan relay replaced, you will pay, on average, $80-$160, depending on the type of car you have and the mechanic's fees. The labor should cost around $70, while parts should run you $10-$50.

Where is the cooling fan sensor?

The cooling fan relay is normally located in either the underhood fuse and relay center or mounted to the electric fan assembly behind the radiator.