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Author Topic: Keep those ceiling registers open....  (Read 5139 times)

Offline Repair-man

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Keep those ceiling registers open....
« on: March 16, 2008, 08:32:15 AM »

Airflow is perhaps the most critical aspect of the A/C system. It can drastically affect the way that refrigerant performs in a sealed system, and if the airflow is reduced enough, damage to the compressor can occur. Airflow is affected by several factors:

  • Evaporator Coil Surfaces- (clean or dirty?)
  • Air Filter- (same thing)
  • Ceiling Registers or Duct Dampers- (open or closed?)
  • Blower Speed- (correct for tonnage?)

Your system is matched for proper airflow by measuring the total square footage of the house and applying an established formula to give the necessary CFM (cubic feet per minute) that the blower must provide. The size of the return air filter and the ceiling registers have to be calculated to achieve the proper airflow recommended for your square footage. If you undersize the duct system, the fan motor will struggle to force the air thru. If you undersize the return air, the system will never achieve full efficiency and will cause the coil to freeze up.

Likewise, a dirty surface on the evaporator coil can cause it to freeze  up. Caused by infrequent filter changes and/or leaky return air intakes, this condition is usually not spotted until frost is seen on the outside unit's suction line. Most compressors do not appreciate this much overcooling and reed valve damage can result.

You can prevent certain problems by simply keeping the ceiling registers open as much as possible and try not to shut doors to rooms unless necessary for privacy. Airflow in a closed room is not doing the system any good, as the absence of return air back thru the blower will cause problems. A good visualization of what happens is like when you hold your thumb over a running garden hose. The water in the hose becomes back-pressured, much the same way your A/C sytem does with air. Those air filters might be a bother to change, but well worth the expense of pulling your evaporator coil out for an acid bath.
"It's only expensive if someone else fixes it for you" -
The Virtual Repairman