Walk-In Cooler Defrost

This article is a quick, real-life diagnosis/find by Kalos Services senior commercial HVAC/R tech Eric Mele.


Improper Defrost Timer installation

While servicing this display cooler for an unrelated problem, I noticed the defrost timer installed in a way that will almost certainly cause early compressor failure.

Because this is a cooler (not a freezer), it is set to defrost by simply shutting off the compressor four times per day while still running the evaporator fans. If you look at the timer, you will see that the little pins are flipped four times per 24-hour period.

If you are not familiar with remote coolers and freezers, they are designed to pump down into the condenser/receiver at the end of each cooling cycle by closing a liquid line solenoid and shutting it off via low-pressure control. That is because the areas they control are kept so cold that a good amount of liquid refrigerant would migrate to the evaporator in the off cycle.

The timer was installed at the condensing unit and would stop the condensing unit/compressor from running during the defrost event, but it would not cause the unit to pump down during defrost. This will likely cause a flooded start at the end of each defrost when the liquid refrigerant rushes into the compressor on startup.

There are no interconnecting wires between the evaporator and condenser, which is common on remote walk-in systems. The easiest way to correct this problem is to relocate the defrost timer into the evaporator and break power to the liquid line solenoid valve during defrost. 

The diagram below shows how it was initially connected and then how we rectified the situation.

 

—Eric M.

Related Tech Tips

Changing Refrigerants and Why it Matters to You
  Graphic Courtesy of Danfoss During the week of 9/18/2017, Danfoss put out a lot of great information on global changes to refrigerants and their expected impact on equipment and the industry. This a quick overview of the different types of refrigerants, the reasons for the changes, and some things to watch out for. ODP […]
Read more
Motor Speed - The Basics
How does a typical motor know how fast to run? Typical induction motors are slaves of the electrical cycle rate of the entering power (measured in hertz). Our power in the US makes one complete rotation from positive electrical peak to negative peak 60 times per second or 60hz (50hz in many other countries). That […]
Read more
What is a DIN Rail?
If you do any larger commercial work, you've probably seen a DIN rail without knowing what it is called. It is simply a mounting standard that originated in Germany in the 80s and slowly worked its way over here. DIN rails can be used to mount terminal blocks, relays, starters, breakers, and just about anything […]
Read more

Leave a Reply

Your email address will not be published.

This site uses Akismet to reduce spam. Learn how your comment data is processed.

loading

To continue you need to agree to our terms.

The HVAC School site, podcast and daily tech tips
Made possible by Generous support from