|Dirty Coil Angle #1 (.76"w.c. pressure drop)|
Last week I got a call from the contractor in RI with a couple of static pressure measurements that didn't sound quite right. He explained that during the recent cold spell, most of the rooms being fed by this unit were uncomfortable. He checked the static pressure in the supply duct and only had a .01" w.c. - almost nothing. Measuring before the add-on A/C coil, doing so by removing the high limit switch of the furnace, the tech was able to record a static pressure of .77"w.c.! Most coils have a pressure drop of .20"-.30"w.c. when clean. Since the pressure drop of the coil is .76" (.77 - .01), it was easy to determine that the clogged evaporator was the culprit. Since removing this 10 year old coil that was obviously never cleaned was so labor intensive, the tech was able to sell a new coil that will be compatible with DOE SEER minimums when the time comes to replace the condensing unit.
|Dirty Coil Angle #2|
If the technician was never armed with the necessary tools and knowledge, it would have been easy to start replacing motors and searching for disconnected ductwork. After all, mechanical systems are much easier to fix when you know what the answers are. Static Pressure, like temperatures or amperage, is an invisible thing and we must have the right tools to even quantify them. Start measuring static pressure when commissioning the unit, and during maintenance. It really is amazing what you will find!