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HVAC "short cycling" is a term that describes a furnace or air conditioner that turns on, briefly generates heating or cooling, then shuts off again before the thermostat's temperature setting has been achieved. A unit that short cycles not only degrades indoor comfort, it runs very inefficiently, boosting operating costs. Another factor is the excessive wear and tear that accumulates when an HVAC unit turns on and off rapidly. This reduces system reliability and can make early replacement of the unit necessary.
Here are possible reasons for HVAC short cycling during the heating season:
Insufficient airflow. The most common cause of furnace overheating is low system airflow due to a clogged air filter or defective system blower. If the furnace temperature sensor detects excessively high temperatures due to insufficient air circulation, it will shut down the furnace.
Defective flame sensor. A gas furnace's flame sensor continuously senses the furnace's burner flame. If the flame goes out, the sensor shuts off the gas flow to the unit. Inaccurate or erratic sensing due to a defective sensor may cause HVAC short cycling.
Oversized furnace. If the furnace BTU capacity is oversized, the unit may heat certain areas of the house too fast, causing the furnace to cycle off before other rooms are comfortably warm, i.e., HVAC short cycling.
Exhaust flue obstructed. The furnace exhaust flue may become obstructed by leaves, birds' nests, or physical damage to the pipe. A clogged exhaust causes the furnace to overheat and trigger an automatic shutdown, cutting normal heating cycles short.
Issues such as clogged filters and oversizing also cause air conditioners to short cycle. Factors affecting AC cycling include:
Low refrigerant charge. Insufficient refrigerant due to leaks in system components can cause an air conditioner to turn on and off rapidly.
Ice formation on coils. Ice obstructing AC coils may trigger a system shutdown. After the ice melts, the air conditioner may restart. If icing recurs, contact your HVAC contractor for professional service.
For more about problems related to HVAC short cycling and good solutions, contact the professionals at Air Assurance.