Sunday, February 15, 2015
Checking Airflow is Not Just a Summer Thing
Checking for proper airflow is not just a summer thing. Most techs know that poor airflow is the first thing you should check in the case of freezing up air conditioning coils or lower than normal suction pressures in cooling. We need to be concerned with airflow in the heating season as well. In fact, in the case of heat pumps, airflow is arguably more important in the heating season because the indoor coil is now the condenser. Sure signs of an airflow problem in a heat pump are low suction pressures and icing in the summer and frequent high pressure switch trips in the winter. I have heard several stories about systems which techs “fixed” by adding charge in the summer and taking it out in the winter. In effect, they are overcharging the system in the summer and undercharging it in the winter. Of course this kills both system efficiency and the compressor. In the summer, the overcharge causes liquid dilution of the compressor oil, and in the winter the undercharge makes the compressor run hot. Other signs of poor airflow include open fuse links on strip heaters, open strip heaters, or open thermal limits which eventually fail from opening and closing repeatedly. In gas furnaces, poor airflow will cause a higher than normal temperature rise. In the case of gas furnaces, it is possible to have too much airflow. Too much airflow will reduce the temperature rise below the minimum, which can cause condensation in heat exchangers which are not designed for condensation. Typical temperature rise for mist furnaces is between 40°F and 70°F. However, check the data plate on the furnace for the exact specification.