Far better it is to dare mighty things, to win glorious triumphs, even though checkered by failure, than to take rank with those poor spirits who neither enjoy much nor suffer much, because they live in the gray twilight that knows neither victory nor defeat.

Theodore Roosevelt, The Strenuous Life

By , on December 11, 2010

Miscellaneous Comment


Strange things occur when the air flow through a residential furnace or indoor air handler is too low. Here are some consequences when in heating mode:

  • The difference between the inlet temperature and discharge temperature increases proportionately with the decrease in airflow.
  • The rate of heat transfer decreases.
  • The appliance temperature rises enough to cause it to cycle on and off very quickly as the automatically resetting  high temperature limit switch opens and closes. This switching causes the furnace or exterior condensing unit for a heat pump to cycle on and off quickly. This “short-cycling” will damage the starter contacts and will shorten the life of the equipment. It will also be difficult to keep the house warm. Failure of the limit switch in the closed (on) position can cause a fire if it is controlling a furnace.

A few of the causes of short-cycling are:

  • plugged air filters.
  • coils caked with dirt.
  • closed balancing dampers or registers.
  • collapsed ducts.
  • dirt caking on turning vanes.

I hope this helps you.



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