Fundamentals: Charging A New System

September 28, 2002
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The work: A new A/C system installation.
The apprentice: Allen Charles Edwards (ACE) — first-year mechanic.
The technician: N. Arthur Thomas Egan (NATE) — 15-year HVACR veteran.

Nate and Ace are installing a new cooling system. They have followed the manufacturer’s instructions that came with the equipment. As required by the instructions, they have evacuated the system to 500 microns. The system is precharged with enough refrigerant for installation with a 15-foot line set. If the installation line set exceeds the precharged amount, they were instructed to add 1.2 ounces of refrigerant for every foot the line set exceeds the 15-foot limit.

NATE: “Ace, what do you think will be the best way to charge this system?”

ACE: “Nate, this is a new system, and I think we should charge the system using the weigh-in method. Then we can confirm the charge using the superheat method, since this is a capillary tube system.”

NATE: “Good, Ace. Tell me, how are we going to do this?”

1

ACE: “The first thing I’ll need to do is determine the maximum length of the tubing.”

The maximum length is:
a) 50 feet
b) 51 feet
c) 52 feet
d) 53 feet

2

ACE: “The next thing to calculate is the amount of tubing in excess of the manufacturer’s 15-foot line set allowance.”

What is the excess?
a) 30 feet
b) 37 feet
c) 43 feet
d) 52 feet

3

ACE: “Next, I will determine the amount of refrigerant that should be added to the system.”

How much refrigerant should be added?
a) 62.4 ounces
b) 51.6 ounces
c) 44.4 ounces
d) 36.0 ounces

4

ACE: “Then I will weigh in the proper amount of refrigerant.”

How much refrigerant will be weighed into the system?
a) 2 pounds, 4 ounces
b) 2 pounds, 12.4 ounces
c) 3 pounds, 3.6 ounces
d) 3 pounds, 14.4 ounces

NATE: “Ace, with the way you’re progressing you’ll be running your own service truck soon. Let’s get this system charged up and then we’ll confirm the charge.”

AUTHOR’S NOTE
Please remember no question appearing in these articles is on a NATE exam. These questions and dialogue are my creation alone. The NATE Technical Committee does not review the article content, and the committee has the final decision for the use of a question on the tests.

Interpretation of codes, regulations, and standards comes from my experience as a technician and a contractor. Different jurisdictions have varying interpretations. The particular area a job is being done in will dictate which viewpoint is to be properly used.

I learn a lot from your commentary and try to incorporate information into the next article, so please continue to comment.

Patrick L. Murphy
Director of Technical Development
NATE
pmurphy@natex.org

Answers: 1) c; 2) b; 3) c; 4) b.

Murphy is director of technical development, North American Technician Excellence (NATE). If you have any further questions or comments on this Fundamentals quiz, contact Murphy at pmurphy@natex.org (e-mail).

Publication date: 09/30/2002

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