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HVAC School - For Techs, By Techs

Sep 13, 2018

Chris Stevens from HVACR Videos on YouTube comes onto the podcast and talks about some refrigeration temperature controls basics. You can check out his YouTube channel HERE.

Although we have temperature controls in HVAC work, we will see slightly different ones in refrigeration work. The biggest difference is really the temperature itself; we're attempting to bring the box temperature down, so we will be dealing with much lower temperatures in refrigeration. The box and evaporator coil temperatures are the most important temperatures to be aware of in reach-in refrigeration, as they directly relate to pressures.

A standard pressure control opens or closes when pressures fall or rise. Your typical low-pressure control will open on a pressure fall and close on a pressure rise. We can use these as loss-of-charge switches or use them with the pressure-temperature relationship as evaporator temperature controls. However, pressure controls can be quite inaccurate. You absolutely CANNOT "set it and forget it" with these controls; you will likely have to make some adjustments, especially if you have long line sets. We also need to consider defrost in our strategies.

Constant cut-in controls are other common control strategies. These are simple controls with a sensing bulb in the evaporator coil that senses evaporator temperature as closely as possible without being a pressure control; they also turn on at a set temperature. These refrigeration temperature controls are quite accurate, but they can be difficult to use properly because they also pick up lots of other vital signs from the system.

Chris and Bryan also discuss:

  • TD vs. delta T
  • K-type thermocouple calibration
  • Wrap-up procedures for refrigeration jobs
  • Self-defrosting with pressure controls
  • Constant cut-in control sensing bulb placement
  • Service gauges
  • Frost buildup in medium-temperature applications
  • Digital controls
  • Controls based on product temperature
  • Universal and aftermarket controls
  • Air-sensing temperature controls

Learn more about Refrigeration Technologies HERE.

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