Fundamentals: Preparing To Charge The System

June 23, 2002
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The work: Replacement, start-up, and check of an existing air conditioning system condensing unit.
The apprentice: Allen Charles Edwards (ACE) — first-year mechanic.
The technician: N. Arthur Thomas Egan (NATE) — 15-year HVAC/R veteran.

Nate and Ace are replacing a 30,000-Btu cooling system. The new system is a 10 SEER. They have removed the refrigerant by following the refrigerant handling requirements of Section 608 of the Clean Air Act. Having completed the component installation, including a new condensing unit, properly sized refrigerant lines, and a matching cooling coil with a thermostatic expansion valve (TXV), they are preparing to charge the system. The design temperature of the home is 76 degrees F with a system charged with R-22.

NATE: “Tell me Ace, what charging method are we going to use on this equipment?”

ACE: “Let me go get the installation and charging instructions that came with the equipment and I’ll be able to tell you. Well, according to the charging charts, we’ll use the method for a system with a TXV.”

1

NATE: “Good, Ace. What information do we need to have to make sure the system is properly charged using the charts?”

a) Type of metering device, gauge suction pressure, suction line temperature in degrees Fahrenheit, gauge liquid line pressure, indoor air temperature, and outdoor air temperature.

b) Type of metering device, gauge suction pressure, suction line temperature in degrees Kelvin, gauge liquid line pressure, indoor air temperature, and outdoor air temperature.

c) Type of metering device, gauge suction pressure, suction line temperature in degrees Kelvin, absolute liquid line pressure, indoor air temperature, and outdoor air temperature.

d) Type of metering device, absolute suction pressure, suction line temperature in degrees Kelvin, gauge liquid line pressure, indoor air temperature, and outdoor air temperature.

2

NATE: “Good choice, Ace. Now I’m going to give you a list of information for three systems. You have to tell me if each system is properly charged using the charts.”

Data Information:

System 1: Metering – TXV; Suction Pressure – 72 psig; Suction Temperature – 56 degrees F; Liquid Pressure – 230 psig; Indoor Air Temperature – 76 degrees F; Outdoor Air Temperature – 90 degrees F.

System 2: Metering – TXV; Suction Pressure – 68 psig; Suction Temperature – 50 degrees F; Liquid Pressure – 210 psig; Indoor Air Temperature – 77 degrees F; Outdoor Air Temperature – 90 degrees F.

System 3: Metering – TXV; Suction Pressure – 68 psig; Suction Temperature – 66 degrees F; Liquid Pressure – 240 psig; Indoor Air Temperature – 77 degrees F; Outdoor Air Temperature – 90 degrees F.

Answer: System 1? System 2? System 3?

NATE: “Nice job, Ace. Let’s go charge the system.”

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) a; 2) System 1: Properly charged (within 2 degrees F of setpoint); System 2: Undercharged (within 2 degrees F of setpoint); System 3: Overcharged (within 2 degrees F of setpoint).

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: 06/24/2002

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