Air Conditioner Thermostats & What They Do

Appliance temperature controls

What’s a Thermostat?

All heating and cooling devices contain at least one thermostat; otherwise, they wouldn’t know when to stop heating or cooling. A thermostat simply controls whether a device is operating or not. It doesn’t control the rate of cooling or heating. Turning the thermostat down to its lowest setting will not make the room get colder any quicker.

Early technology relied on the expansion and contraction of certain materials when heated or cooled. The expansion of mercury was often used to complete a circuit when it expanded in a chamber. Bi-metallic strips had one metal that expanded at a different rate which made the strip bend at a set temperature, again completing a circuit.

More recent developments include thermistors that have different electronic resistance at different temperatures and thermocouples that produce a current when heated. Mercury is banned in thermostats due to its toxicity but we still find old ones in use. Old mercury thermostats need to be disposed of by a registered company, not just thrown out with the trash.

Thermostat Applications

Some appliances that have thermostats are quite obvious, such as a clothes iron or a refrigerator. As you adjust the temperature on either, what you are in fact doing is altering the point at which the thermostat activates. On an iron, as you turn the knob to increase the temperature, you increase the point at which the bimetal strip heats up and expands sufficiently to break the electrical contact to the heating element, often with an audible click. On a refrigerator, the opposite is happening.

As you lower the temperature, the electrical contact with the cooling compressor is maintained until the temperature is low enough. Almost every electrical device that you own will have at least one thermostat, if only to prevent overheating. Often these fuses will reset themselves as the device cools down, but in some cases, the fuse blows and will need to be replaced by a specialist like those we have here at West Coast Chief Repair.

Signs of a Faulty Thermostat

Sometimes the air conditioning won’t start there are many possibilities for this but if the thermostat is malfunctioning and sending the wrong reading, the whole system may fail to turn on or to turn off. Climate fluctuations from room to room and a blank screen are other indications.

Fixing an Air Conditioning Thermostat

Of all the parts of an air conditioning unit, the thermostat (also known as the control panel), is one of the easier components to service. If you are going to attempt anything yourself, ensure power to any devices that you are working on is turned off and any other appropriate safety measures are in place.


Not all thermostats have batteries, some are powered by the main electricity supply but others have standard batteries that can be changed relatively easily. Methods and models vary but the unit will normally unclip after loosening a couple of retaining screws. Two AA/R6 batteries are the norm and should be located in an obvious position, replace them and put everything else back as you found it.

Dust & Dirt

Everything in the home gathers dust and dirt in time. Use the same method of unit removal as above and using a soft brush, clear any dust or buildup of dirt. Conversely, over-zealous cleaning can knock the unit off balance, make sure it’s level when it’s put back.


If the position of the thermostat is not representative of the rest of the house, then it will turn the AC on and off at the wrong temperatures. Make sure there’s nothing producing heat nearby, like a computer or direct sunlight. Due to the complexity of even the most basic home electrical appliances, the kind of specialist that visits your home will depend on the problems that your equipment exhibits.

Other Thermostatically Controlled Domestic & Commercial Appliances

West Coast Chief Repair engineers are trained in dealing with all makes of domestic appliances and regularly update their skills to keep them abreast of the most modern developments. If for example, your clothes dryer is not getting hot enough or your dishwasher is leaving the dishes wet, these are possible indications that there is a problem with the heating control system that may be due to a faulty thermostat.

A hot plate that gets hot enough only to cool down before heating up again could point again at a fault in the thermostat control system. Call us in the morning, and we can be with you the same day. We’ll have your appliance up and running again as soon as possible.


Refrigeration is another specialty of ours. Due to the gasses used and the very cold temperatures that are reached, all our engineers that deal with refrigeration and freezers are trained specialists. We are mindful of the possible loss of chilled and frozen foodstuffs, so we will be with you as soon as possible to repair and recalibrate your thermostats.

Heating, Ventilation & Air Conditioning (HVAC)

This is one of the most complex areas with several thermostats and thermocouples in various areas of the system. If one should become faulty, it can shut your whole system down or cause part of it to act erratically. Having a detailed knowledge of HVAC systems can help pinpoint the problem quickly and efficiently. Part of the problem for the non-specialist is that so many parts are interlinked that a problem showing in one area can be caused by a component in a different part of the system.

This is why our specialists are constantly training and updating their skills. At a time that is convenient for you, our engineers will call and have your system back up and running. At the same time, they can even offer suggestions as to how to make your system operate more efficiently. One of the best ways to reduce your heating and cooling costs is to replace an old room thermostat with a Smart Thermostat. Smart thermostats are so efficient that many utility companies, in conjunction with the EPA, offer discounts for having them fitted.

A modern thermostat can keep your temperature within 1 degree of your setting, rather than overheating or overcooling your room. Many of the Wi-Fi-enabled models are linked to local weather reports, and they can adapt your system to use outdoor weather when it is more economical. Some models can detect when there is no one in the house and switch the temperature to your standby setting. When you return, the thermostat will detect movement and switch the system back on.

Repairing Residential Thermostat Controls – Just One of Our Services

We at West Coast Chief Repair offer a comprehensive service for air conditioning, refrigeration, and domestic appliances, 6 days a week (excluding Sundays). We are usually available to visit your home anytime between 8 am to 6 pm.



Related AC Pages