Question: What is the best way to charge a residential a/c unit and why? How can you tell when a residential a/c unit is properly charged?

-E. J. Monahan, Burbank, Ill.

Answer: Air conditioning and heat pump units are somewhat like other things in this life. No two of them are the same.

The best and only way to charge a/c-heat pump systems is to follow the manufacturer's recommended procedures for the model. If the unit is cooling/heating according to the manufacturer's specifications, then it is operating correctly. Contact the manufacturer, obtain the unit's specifications and verify if it is operating within these conditions. If it is not operating within the design conditions for the unit, corrections must be made.

With the many variables encountered in the average installation, problems can range from selecting the wrong unit for the job to incorrect sizing. Poor installation practices at any phase can create problems that adversely affect the operation of the system. This would include duct design and installation, and proper placement of all components.

The service engineer called to repair or service a unit must be very diligent in his diagnostic procedures to locate the problem. There is much more to proper servicing an a/c unit than adding refrigerant. Problems can range from restricted airflow over the coils to electrical/control problems. All may appear as refrigerant problems.

-Frank Fulkerson, consultant, Weaverville, N.C.