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Replace Commercial Refrigeration Thermostats Yourself

There are two types of temperature controls used in commercial refrigeration:

1. Thermostatic (either an air sensing type or evaporator coil sensing type)
2. Low pressure controlAn Air Sensing Refigeration Thermostat

Let’s start with thermostatic type controls.  An air-sensing thermostat does just that: it senses air temperature.  The control sensor tube is usually mounted in the evaporator housing.  The evaporator is located inside the unit, usually at the top where the fan motor is mounted.  The thermostat has a straight capillary or sensor.  The capillary tube is mounted on the outside of the evaporator coil usually pushed into a tube that is mounted in the front of the evaporator.

An Evaporator Coil Sensing ThermostatAn evaporator-sensing thermostat has a coiled capillary tube attached to it, which you can see pictured as a tight spiral to the left.  The evaporative sensing capillary or coiled tube end push into a hole that is in the evaporator.  It senses the temperature of the evaporator coil rather than air temperature.

These two controls are not interchangeable. If you put an air sensing control in place of an evaporative sensing control, the evaporator unit will shut off permanently, causing the temperature to rise.  If you put an evaporative sensing control in place of an air sensing control the unit will continue to run, causing the evaporator to freeze up.  If this happens there will be very little airflow, causing the temperature to rise.

How to spot a defective thermostat:

A commercial refrigeration thermostat can fail in two ways: in an open position or a closed position.

If the thermostat fails in the open position, the unit will not run at all.  To check this, remove the screws from the evaporator housing (make sure the unit is unplugged or the breaker is off) and pull the housing down.  Locate the wires attached to the thermostat and remove them.  Connect the two wires together and tape with electrical tape.  Turn on the breaker or plug the unit back in.  If the unit runs, replace the thermostat.

If the thermostat fails in the closed position, the unit will run all the time.  Running constantly will cause the evaporator to freeze up, restricting the airflow and causing the temperature to rise.  Use the same procedure described above to test the unit and replace the thermostat if necessary.  Also be sure to defrost the evaporator before turning the unit back on.

If the evaporator continues to freeze up after the thermostat replacement, call a service company as you may have other problems requiring a trained technician.

The other type of control is a low-pressure control.  These are usually located in the compressor compartment.

A low-pressure control is connected into the refrigeration lines and controls the temperature by using the pressure of refrigerant flowing through the line.  This type of control requires a service technician to replace.

About Greg McGuire

Greg has blogged about the food service industry for years and has been published in industry magazines, like Independent Restaurateur and industry blogs like Restaurant SmartBrief. He lives in Colorado with his wife and two sons and enjoys reading, live music, and the great outdoors.

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26 comments

  1. My Cavalier brand beverage box runs all the time even after I replaced the thermostat. What do I look for in order to locate the problem?

    • Hi Frank,

      It sounds like your thermostat may have frozen up in the closed position. You will probably need a service tech to help you troubleshoot the problem. Also make sure you have defrosted the evaporator and that it is getting good airflow.

  2. I fully charged my cooler and its running but doesn’t seem to be blowing cold air.
    Does any one know whether this would be a relay or thermostat problem?
    Thank You

  3. How long should it take to replace a thermostat in a commercial refrigerator?

  4. my temperature knob on a True unit is off center so the coldest setting is at 4. Is there a way this could keep my refrigerator from getting to the coldest or does it not matter?

    • Hi Alyssa,
      The plate with the numbers on it is just that, a plate with numbers on it, the control doesn’t know what it’s pointing at. Now lets talk about those controls. The mechanical controls are adjustable, but the factory doesn’t recommend adjusting to the “coldest” setting.

      “Excessive tampering with the control could lead to service difficulties. Should it ever become necessary to replace temperature control, be sure it is ordered from your TRUE dealer or recommended service agent.”

      If you’re having problems with your unit not getting cold enough and you already have that control set at it’s lowest setting then you either need a new thermostat or the condensing coil needs to be cleaned. Or both. That unit should only require slight adjustments to the thermostat. It leaves the factory set to number 5 and that is designed to get the unit to 35 degrees. Any adjustments to that should be made in ½ number increments, but too many people think they should just turn it all the way down. If the unit runs too long your coil inside will start to freeze and then the box will get warm.

      I would say the first step would be to get that coil cleaned really well and set the thermostat to the middle of it’s range and give it a day to see what it does. If the fans are strong and the coils are clean then you need a new thermostat.

      – Paul
      Tundra Team

  5. For an evap. sensing thermostat, where is the best location to place bulb in evap. coil in relation to length and width of coil? Middle length ways, middle height? Entrance end of coil, middle height? Etc.

    • Bee,
      Every manufacture is going to answer this a little differently about their units. I would say a general answer to this is: Most coils have a tube on one end that is open and that is where you would insert the sensing end of the control. This is usually found toward the top of the coil as the refrigerant is entering the bottom of the coil as a liquid and leaving the top as a vapor after it’s absorbed the heat from inside the box, so you don’t want the control sensing the colder liquid as it comes in and would shut off the unit prematurely.

      – Paul
      Tundra Team

  6. The compressor, evap fan and condenser fan are all working properly. There’s enough freon inside the compressor. However, the temperature would not go lower even when I turned the thermostats all the way to the coldest postilion. The unit turns on and off like normal. It’s just not cold enough. (Was fine couple months ago) Any idea? Thank you very much.

    • The mechanical controls are adjustable, but the factory doesn’t recommend adjusting to the “coldest” setting:

      “Excessive tampering with the control could lead to service difficulties. Should it ever become necessary to replace temperature control, be sure it is ordered from your approved dealer or recommended service agent.”

      If you’re having problems with your unit not getting cold enough and you already have that control set at it’s lowest setting then you either need a new thermostat or the condensing coil needs to be cleaned. Or both. That unit should only require slight adjustments to the thermostat. It leaves the factory set to number 5 and that is designed to get the unit to 35 degrees. Any adjustments to that should be made in ½ number increments, but too many people think they should just turn it all the way down. If the unit runs too long your coil inside will start to freeze and then the box will get warm.

      Paul
      – Tundra Team

  7. Hi there I have a small commercial bottle cooler with a coiled bulb at the end of the thermostat but it was placed under the evaporator not init . So I replaced it with a straight bulb but fridge cuts in and out every 5 min

    • Neil,
      It sounds like the first one was an air sensing thermostat and below the coil where the air is first introduced to the coil was the correct place for it. I would suggest getting the Make, Model and Serial number from inside the unit and give us a call at 1-888-388-6372 to buy the correct thermostat for your unit.

      – Paul
      Tundra Team

  8. I’ve got a TRUE merchandiser cooler that would just be TOO COLD, that my soda freezes and pops. I’ve just replaced the thermostat and confirmed with the seller to match the model and serial number ( resulting in TRUE988287 TEMP CONTROL KIT 077B6871)

    When I removed the old thermostat, I was surprised to see the coil curled like a spring (as if new) instead of straightened out over the width of the fridgerator. Anyway, I decided to let the coil go to the back and down the length of the cooler.

    1) Is that ok?
    2) It’s still too cold, even at the lowest setting (1). Help please.

    • Tundra Restaurant Supply

      Hi Khanh,

      True has been putting out thermostat retrofit kits lately and you should contact the factory for assistance at 636-240-2400.

      Tundra Team

    • I am having the exact same issue with a True 5244843 unit..Worked fine for 3 years..Replaced the thermostat with generic therm, it froze everything, would not adjust..Called technician, he replaces it with a True thermostat and the same thing happens..It’s either off or frozen at 29 degrees..I’m so frustrated with this unit..The technician has” no idea” what’s wrong either..Please let me know if you get your problem figured out!

  9. Hi, I had to replace a compressor for a custom built commercial drawer cooler. The compressor had blew out the common pin and system lost all refrigerant. Once I replaced compressor I pulled vacuum on system and then added proper charge of 404A . Their is a low pressure switch installed in system. My condensing fan came on but compressor would not. I thought I had not charge unit enough so I added very little gas an oz at a time but compressor would never start. I by passed switch and compressor would run but unit would not cool. Any suggestions on what problem may be?

    • You could have a bad Low Pressure switch and put too much gas in before you bypassed it, too much gas means high pressure = high temps. Also, did you run a nitrogen pressure test before vacuuming? Do you have a blocked capillary tube? There’s so many variables to your issue. You could always consult the factory for more info.

      – Paul
      Tundra Team

  10. Hello, I am working on an Imbere G-319 cooler. The problem is that its not cooling. All fans are running as well as the compressor. It has an electronic thertmostat which like most is the sensing tube which is mounted in the evap. Please provide feedback. Thank you. Jerry

  11. Hi Jerry,

    This unit needs to be inspected by a licensed technician. Chances are you have a leak or a bad compressor.

    – Paul
    Tundra Team

  12. Hi Jerry
    I have a beverage air single door soda cooler and I cant seem to control the temp, even at the warmest setting I am getting temps in the 20’s. I set it on the med. setting and returned hours later and it was 16 Do you think it is jest a thermostat that needs replacement?

    • Hi Charles,

      Most likely that is correct. The mechanical thermostats are very finicky. If you move the knob too much they will break. You should install a new one and leave it alone for a day to settle and make small adjustments and leave it alone to see how it performs. It’s a tedious process, but it’s worth it in the end.

      – Paul
      Tundra Team

  13. Hi Mr. Paul I been working in a salad cooler,I will like to know what’s my next step, the unit was not cooling lower than 50 degree F, so I check my low reading on gages and my result was 25 psi on low, I add refrigerant
    and the next day the unit still the same, I replace compressor, the dry filter, and then capillary tube, then add nitrogen, then vacuum the system, and then add new R134a and last start the unit.
    Now the compressor get cool and the inside the evaporator still the same temperature of no less than 50 degree, what can I do to repair this problem, to maker normal like new again.
    Any suggestions.
    Please respond thanks Erick

    • Hi Erick,

      Sorry for the delay, but unfortunately your issue sounds too deep to troubleshoot over a blog. I suggest reaching out to the manufacturer for advice or hire another refrigeration company.

      – Paul
      Tundra Team

  14. I have a commercial refrigerator for soda and the sodas have burst open. What is causing this?
    I have not changed the temperature since I bought it.

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