HVAC School - For Techs, By Techs

Short #67 - Defrost Termination and Failsafe


Listen Later

In this short podcast episode, Bryan quickly covers defrost termination and failsafe. He also explains what they mean in refrigeration systems.

We need to defrost evaporator coils anytime they drop below freezing (32°F, o°C). When evaporator coils have a coat of ice over them, they cannot transfer heat from the box to the refrigerant; the ice blocks the coil from the air in the box. In defrost, we add heat to the evaporator coil. We can add heat in the form of electric heat or hot gas (discharge gas); either of these can damage product if they run too long. A simple off-cycle defrost may also work on properly sized coolers and medium-temperature equipment.

We can control defrost by fixing the cycle onto a timed schedule. Unless we can use a complicated algorithm with a series of sensors, we almost never initiate defrost based on temperature. Instead, we initiate defrost based on a timed cycle. The defrost termination relies on a thermostat or control to stop the defrost, so a defrost will end early based on a temperature reading (since it will be well above freezing). After the defrost ends, there may also be a dwell time where the coil can drain its moisture before the refrigerator starts cooling again; that way, the moisture won't freeze back onto the coil when the system starts operating again.

If the defrost termination fails to kick in, we need to set a defrost end time to take the system out of defrost. We call that end time the failsafe. It is not a good idea to use the failsafe to predict the defrost cycles; it should only work in the case of emergencies.

So, to sum things up, defrost termination relies on temperature, but failsafe relies on time.

 

Learn more about Refrigeration Technologies HERE.

If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

...more
View all episodesView all episodes
Download on the App Store

HVAC School - For Techs, By TechsBy Bryan Orr

  • 4.9
  • 4.9
  • 4.9
  • 4.9
  • 4.9

4.9

985 ratings


More shows like HVAC School - For Techs, By Techs

View all
The Ramsey Show by Ramsey Network

The Ramsey Show

38,679 Listeners

The EntreLeadership Podcast by Ramsey Network

The EntreLeadership Podcast

4,330 Listeners

The Contractor Fight with Tom Reber by Tom Reber

The Contractor Fight with Tom Reber

408 Listeners

The Fine Homebuilding Podcast by Fine Homebuilding Magazine

The Fine Homebuilding Podcast

771 Listeners

Zack's Shop Talk by Zack Psioda

Zack's Shop Talk

152 Listeners

Building HVAC Science by Bill Spohn

Building HVAC Science

71 Listeners

The Home Service Expert Podcast by Tommy Mello: $200 Million Founder|Forbes, Inc., Entrepreneur Columnist

The Home Service Expert Podcast

721 Listeners

HVAC Know It All Podcast by Gary McCreadie

HVAC Know It All Podcast

208 Listeners

Hvac Uncensored by Gil Cavey

Hvac Uncensored

112 Listeners

HVAC Tech Tips by CE

HVAC Tech Tips

16 Listeners

AC Service Tech Answers Podcast by Craig Migliaccio

AC Service Tech Answers Podcast

89 Listeners

Waste No Day: A Home Services Motivational Podcast by Brian Burton & Nate Minnich

Waste No Day: A Home Services Motivational Podcast

468 Listeners

The Build Show Podcast by Matt Risinger

The Build Show Podcast

359 Listeners

The Refrigeration Mentor Podcast by Trevor Matthews

The Refrigeration Mentor Podcast

29 Listeners

Did You Know?-The ESCO HVAC Podcast by ESCO Institute

Did You Know?-The ESCO HVAC Podcast

6 Listeners