(Audio Only) In this episode of the HVAC School podcast, Dick Wirz, author of Commercial Refrigeration for Air Conditioning Technicians, talks about making the switch from A/C to refrigeration.

Dick Wirz is an advocate for using rules of thumb, which is a controversial position. However, rules of thumb are an excellent way for A/C techs to dip their toes into the refrigeration world. Rules of thumb are less likely to overwhelm technicians than the exact technicalities of certain readings and measurements.

Some prime examples of using rules of thumb in air conditioning are condenser split, evaporator split/TD, subcooling, and superheat. Those all have relatively neat “rules of thumb” that don’t vary too much. (30-degree condenser split, 35-degree evaporator TD, 10-degree subcooling, and 10-degree superheat.) On medium-temperature refrigerators, a common rule of thumb is a 10-degree TD for a 35-degree box with an evaporator running at 25 degrees (35 – 10 = 25). On low-temperature applications, the box temperature is -10 degrees. You still have the 10-degree TD, so the design conditions for the evaporator would be -20 degrees (-10 – 10 = -20). The pressures will vary across refrigerants, but the temperatures WILL REMAIN the same as the rule of thumb.

Ice is an alarming sight for residential technicians. However, commercial refrigeration technicians will occasionally see frost or ice under perfectly normal circumstances. Frost merely indicates that the temperature of a pipe is below freezing. Ice alone does NOT indicate floodback. In commercial refrigeration, the fans run all of the time to defrost the system (even during the off cycle). However, in freezers (low-temperature refrigerators), hot gas or electric defrost is required.

Dick also talks about:

Subcooling vs superheat in diagnosis
R-410a pressure confusion
Reach-in and walk-in refrigerators
Medium and low-temperature refrigerators
Defrost controls
Common issues in commercial refrigeration

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21 thoughts on “Commercial Refrigeration for A/C Techs w/ Dick Wirz

  1. hvac01453 says:

    I must agree. Both Dick and Dan are my two favorite writers in this industry.  I contacted Dick and got a response just before he was going on Vacation, and he still responded.  Is the third edition just a copy of edition of two?   Love his diagrams on the freeze and defrost cycles with the two wire and three wire stats.  One thing I found weird.  The three wire fan delay typically cuts in the fans at about 25F, to refreeze the water on the coil to prevent the water on the coil from spitting water on the floor or ceiling.
          My local supply house only carries ones that cut in at 35F…. Doesn't this defeat the whole purpose of the fan delay (above 32)??? Im thinking there must be a manufacturer installing these, otherwise, why would you even make them?

  2. G. Martinez says:

    Thank you for this podcast. It was very informative and helpful for newer techs like myself. I'm going to order this book this week and dive in. This series is greatly contributing to our industry as a whole, so thank you and keep up the good work Bryan!

  3. Quang Nguyen says:

    When the stat probe stick into the evap which at 20F then the stat contact break before the box temp satisfy. How you deal with that? Using a stat that has a at least 20F differential between box and evap temp? I wish dick Wirz has super market refrigeration video training

  4. Aaron Cruz says:

    I'm a few years late on this podcast, but, this conversation couldn't be more relevant to my situation right now. It honestly had me a little chocked up at some points. Especially when it was mentioned about being thrust into the refrigeration world and coming from hvac. I rented the book through Amazon. It has been very beneficial so far. Thanks 👍

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