Which Device is Used to Control the Temperature in a Walk In Cooler or Walk In Freezer?

Updated: Apr 14

Your walk-in cooler is warm, isn't it? You wouldn't be searching the internet trying to find more about the parts of your walk-in unless you were having trouble.

Well, I've got an answer for you. What controls the temperature in your walk-in cooler? The thermostat.

Most old home A/C and heat thermostats use a super simple thermostat which consists of two different metals 'glued' together. Those glued together metals expand at a different rate when heated or cooled and bend. That bending makes an electrical connection and acts as a switch. The warmer the metals get the more they bend as one expands at a different rate than the other. This is what turned on the heating or cooling in your grandparents house back in the day. Today we rely on thermostats that have a lot more bells and whistles but effectively do the same thing.


The most common temperature control for your walk-in cooler or freezer is based also upon expansion or contraction of a substance to decide when to turn the cooling on and off. That substance is a gas. In the picture below you'll find the most common temperature controls for a walk-in. It is called a mechanical temperature control. It is called this because it does not rely on anything electronic to decide if it needs to turn the cooling on or off. When the temperature drops the gas contracts and shuts off cooling. When the temperature rises the gas expands and turns on the cooling. The thermostat depicted below has a long copper tube with a bulb at the end of it. The bulb is where the temperature is taken and gas in that long tube changes pressure and turns the switch on and off in the thermostat. This allow you to put the thermostat somewhere accessible while putting the bulb on the rear of the evaporator in the place you actually want to get the temperature.

Mechanical refrigeration walk in thermostat

The Most Common Austin Mechanical Walk-in Temperature Controls

This mechanical thermostat technology has been around for a long time and technology has advanced to smarter temperature controls with electronic sensors. The one depicted below uses a wired electronic probe to determine temperature. This probe uses a thermistor to calculate the temperature by monitoring the resistance through the probe. As the thermistor gets colder the resistance rises and the circuit board in the thermostat works out what the temperature is based upon pre defined resistance. One of the very useful things about this type of control is that the thermostat does not need to be anywhere near the evaporator. The cable that goes to the probe can be quite long allowing the thermostat to be mounted somewhere convenient to easily be seen. The control board senses the temperature from the probe and activates a relay to turn on the cooling. The downside of this type of thermostat is that there are more parts to fail. The simplicity and affordability of the mechanical temperature control often win out over the more intelligent controls.

A Typical Austin Electronic Walk-in Thermostat

digital refrigeration walk in thermostat

If you do not see one of the two temperature control options above on your walk-in cooler or freezer you may have a refrigeration control system as seen below. Refrigeration manufacturers decided to improve upon the mechanical and electronic temperature control by having an all in one control that does it all. It controls the refrigeration like a regular thermostat using thermistors but it also controls the defrost cycles.

Wait. What is a defrost cycle? All coolers and freezers need their evaporator to be defrosted from time to time. Moisture in the air condenses on the evaporator coils and turns to ice. If a defrost cycle does not happen every once in a while that ice will cover your evaporator coil, air can no longer get through the coil and your walk-in starts warming up. How does it defrost the ice? In a cooler it just shuts off the refrigeration but leaves the evaporator fans running a few times a day and all of the ice melts off. A freezer needs heaters to melt the ice from the coils. Why? Because the inside of your freezer should never be above freezing so just running the fans would never thaw out the ice on the evaporator coil. Another thing about a freezer defrost cycle is that the evaporator fans do not run during defrost. Don't be freaked out if the fans in your freezer shut off four times a day. It's a planned part of the defrost and keeps everything running normally.

Most defrost is done with a couple of other parts in the refrigeration system: A mechanical clock that tells it when it is time for a defrost and cool little device called a klixon that measures temperature to determine if all of the ice is gone. The klixon is only on freezers or beer caves which run at or below freezing. The refrigeration control system replaces the mechanical time clock, the klixon and your thermostat. One of the great advantages of this smart system is that it is more energy efficient. It is motoring the temperatures with thermistors of a couple of places on the evaporator and only does defrosts when it determines it is necessary rather than at a time interval. This save money.


Heatcraft electronic temperature and superheat controller board inside evaporator

Heatcraft Electronic Refrigeration Controls in Austin

Is it always the thermostat, temperature control, or refrigeration control system that causes your walk-in to be too warm? Unfortunately, it is not. There are other issues that can cause your box to be warm which are so numerous it can not be explained in the scope of this blog entry.

Was it too much information about what controls the temperature in your walk-in? Need help with a problem on your walk-in cooler? Give us a call, we have office in Austin, Texas (512) 651-4565 and Lubbock, Texas (806) 787-4985. Or Visit our website at www.tripointrefrigeration.com

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