Murphy's Law: Superheat and Subcooling Important

Look out; a technical incompetent is on the loose. Yes, this could be referring to me attempting to explain the importance of measuring superheat and subcooling, or it could be referring to a technician who just strapped on a set of gauges with nary a clue.

Rough estimates would suggest that there are hundreds of thousands of HVACR technicians getting some windshield time across this vast land, and at least a few of them do not understand this most basic procedure. That is not to say it is simple for everyone to understand (call me Clueless in Cleveland), just that it is a basis for sound refrigerant management. In other words, charging a system after installing a new TXV or compressor could be very difficult if a person does not understand superheat and subcooling.

HOW IMPORTANT IS IT?

Here is a case in point: The bottom of the www.achrnews.com home page has three Top 10 lists - Most E-mailed Articles, Top Searches, and Most Popular Articles. At the time of this writing, Troubleshooting HVACR Systems Using Superheat and Subcooling, Aug. 7, 2006, was No. 1 on the Most Popular Articles list and No. 2 among the Most E-mailed Articles.

For a little added flavor, consider this: Quick Facts: Superheat and Subcooling, June 12, 2005, was No. 2 on the Most Popular Articles list and No. 9 on the Most E-mailed list, and Superheat Charging Curves for Technicians, Aug. 3, 2000, was No. 8 on the Most Popular Articles list.

By the way, these old stories have been appearing somewhere on these Top 10 lists for quite a while.

Hmmm.

It appears that some old stories are still quite popular, and with good reason. People are looking for reliable educational information to make up for a lack of formal training.

According to Patrick Murphy of North American Technician Excellence (NATE), a technician certification body that serves the HVAC industry, “We have found through our testing that only about 25 percent of all technicians have received any formal training. Most learn on-the-job and through a variety of rule-of-thumb methods; as you might guess, this can leave a lot to be desired.”

A few years ago, the NATE organization discovered that basic questions regarding refrigerant charging procedures were being answered better by those technicians who had recently taken classes for the handling of R-410A refrigerant. Conversely, it appeared that those who had only been working with R-22 did not fare as well, and probably because most had never had much training for the refrigerant which many of them had grown up with in the business. The safety concerns of working with a higher pressure refrigerant may have forced many techs to revisit superheat and subcooling while attending either a distributor or manufacturer’s training class on R-410A.

So, the good news is that almost everyone who wants to learn about handling a new refrigerant will be exposed, or re-exposed, to superheat and subcooling methods. The bad news is still the fact that so few people actually get the opportunity to take advantage of such training.

IT'S A NEW DAY

Here is an excerpt from one of the top stories in our list that came to us courtesy of Flow Controls Division of Emerson Climate Technologies.

“When should I check the superheat? The superheat should be checked whenever any of the following takes place: System appears not to be refrigerating properly. Compressor is replaced. TXV is replaced. Refrigerant is changed or added to the system. Note: The superheat should be checked with the system running at a full-load, steady-state condition.

“How do I change the superheat? Turning the adjustment stem on the TXV changes the superheat. Clockwise - increases the superheat. Counterclockwise - decreases the superheat.

“Why is subcooling desirable? Subcooling is desirable for several reasons: It increases the efficiency of the system since the amount of heat being removed per pound of refrigerant circulated is greater. In other words, you pump less refrigerant through the system to maintain the refrigerated temperature you want. This reduces the amount of time that the compressor must run to maintain the temperature. The amount of capacity boost which you get with each degree of subcooling varies with the refrigerant being used.”

Yes, that was simply a teaser - go to our home page to get the full story. Better yet, if it has been years since you actually sat in on a training class, do yourself a favor, and refresh your memory. Don’t rely on old standards like “beer can cold” to get you through the day.

Publication date: 07/27/2009