Proper Refrigerant Charging

Yesterday we were called out to a house by a reluctant homeowner to service her system. I say reluctant because it was only 3 years old and she felt the new system did not need to be maintained. When we showed up we found two things wrong. First, the system was improperly charged, the second was a pending failure precipitated by the low refrigerant charge.

The second most common error in new AC system installations is improper charging. Under or over charge can result in a 20-30% decrease in cooling capacity.

Most new split systems have enough refrigerant for a 15-20 foot length of copper pipe(lineset) connecting the inside and outside units. Most installations have the inside portion located farther away than 20 feet. So if your getting a new system and know this, ask the installers how much refrigerant was added to make up the extra lineset length.

Now about proper refrigerant charging. The proper charge depends on the system installed and the configuration of the equipment. However, regardless of system configuration, the system should have about 10-14 degrees of sub-cooling. Wow, big word here….Sub-cooling is the term used to describe how many degrees the actual refrigerant temperature is below the refrigerant boiling point. This sub-cooling ensures that a steady flow of liquid refrigerant is delivered to the indoor coil. Too much liquid and the system is over charged, not enough liquid the system is under charged, both conditions resulting in low cooling performance and lower reliability.

A interesting fact, more refrigerant does not mean better cooling! If you run liquid refrigerant through the indoor coil and do not achieve a “vapor” state leaving the coil 2 things happen. First, the liquid refrigerant “slugs” the compressor and will cause premature failure. Secondly, the system cooling capacity is reduced by a factor of 10….that’s right the system cooling performance will be decreased.

So before your decide to “add” refrigerant, ask the following questions. Is the outdoor coil clean, what are the current sub-cooling and superheat values, current saturation temperatures and operating pressures for the high and low sides. If they cant answer these questions, your most likely buying something you don’t need, or they have no clue to what they are doing. So be it new or be it and older system, remember, refrigerant charging is a science not a sales technique.

No comments yet