Refrigeration Defrost Termination & Fail Safe - Short 135

HVAC School - For Techs, By Techs

Bryan Orr

Education, Business, Self-improvement, Careers

4.9 • 1K Ratings

🗓️ 14 December 2021

⏱️ 10 minutes

🔗️ Recording | iTunes | RSS

🧾️ Download transcript

Summary

In this short podcast episode, Bryan covers the differences between defrost termination and failsafe. He also covers the basics of defrost in refrigeration applications.

In medium-temp applications (also called coolers), the box stays above freezing temperatures, but the coil may drop below freezing. When the air is above freezing, we can use off-cycle defrost. The coil defrosts when the system naturally cycles off. We may also use timed defrost, which pumps down or cycles the compressor off at set times to force a defrost cycle.

In low-temperature applications, the box will typically be below freezing. We may use electric heat to melt ice off the evaporator coil, and the fan stays off; this method is usually accompanied by a pump-down to remove refrigerant from the coil. We may also use hot gas defrost, which pumps discharge gas through the coil to melt the ice off it. (Kool gas may use a warm fluid instead of hot gas.)

We want to stop the defrost as soon as the coil is ice-free; we don't want to keep adding heat when we don't need to melt anything. A defrost thermostat detects when the coil is free of ice and terminates the defrost when the temperature reaches around 55 degrees Fahrenheit; this is called defrost termination. We rely on a failsafe to terminate the defrost in case the defrost termination fails; the failsafe is the maximum amount of time a system is allowed to remain in defrost.

Demand defrost uses time and temperature to tell the controls when to put the system into defrost; this method uses trend analysis and sensors to force the system into defrost at set times and intervals.

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Transcript

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0:00.0	Why hello there. This is a short episode and therefore it's a short intro of the
0:08.1	HVAC school podcast. This episode is going to be on defrost termination and and Failsafe, so a little bit of refrigeration talk.
0:15.7	We don't do a lot of that. It will be simple. But maybe something for an AC guy might be helpful for you to understand refrigeration a little bit better, maybe a newbie. But before we do that, let's hear about some of our great sponsors.
0:27.0	Refrigeration Technologies and RefriggeTech.com. The Pastorellos, Mike and John, run a great organization and they make some of the best chemicals out there for our trade.
0:38.0	A new product that you're going to want to try out
0:45.0	Nylog White. We've tested out Nylog White. It's designed for air, water, glycol, and gas so you can use it on all of your threaded connections.
0:52.0	It replaces many of your existing pipe dopes. It's a very smooth, it's a very clean
0:57.1	applying product. Comes in a nice clean white container with a thread on brush cap so you can apply your thread sealant
1:06.2	on all of your threaded connections easily and smoothly that is nylon white from
1:11.1	refrigeration Technologies.
1:12.8	Pied out more by going to Refrigetech.com.
1:15.8	Carrier.com
1:18.6	Mitsubishi Electric.
1:20.0	We have been Mitsubishi Diamond Deal, diamond contractors for years and years at
1:25.2	Kailos and Mitsubishi is coming out with more and more innovative products to serve both
1:30.6	commercial and residential as well as high efficiency high performance homes if you haven't looked
1:35.7	at Mitsubishi in a while now is the time to do so find out more at Mitsubishi
1:40.9	comfort.com.
1:42.8	All right, so as an AC tech, and I am an AC tech.
1:47.2	Let's make no bones about that.
1:48.6	I've done a decent amount of refrigeration, but I am an AC tech.
1:51.5	I'm a student of the trade in general, and so I like to learn as much as I can and to be able to teach and all that and in our business we do some refrigeration. But as an AC tech I get the words
	...

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