Fan Runs Continuous
FAN RUNS CONTINUOUS – The thermostat maintains the correct temperature, but the indoor fan never quits blowing.
POSSIBLE PROBLEM & DESCRIPTION
Thermostat "Fan" Switch
The most common cause of this problem is the “Fan” switch on the thermostat. It normally has two options – “Auto” and “On”. In the “Auto” position, the fan should cycle on only when there is a call for cooling. In the “On” position, the fan will run continuously.
Some new thermostats have an additional fan setting of “Circ”, which is short for “Circulate”. In this mode the fan will cycle on and off with the cooling, but it will also kick-on automatically if there is an extended period without a demand for cooling – to provide additional air circulation.
If your system has an added humidifier, this could cause the system to run more than normal.
Some humidification system energize the blower to operate even when the heating system is not running to maintain the humidity setpoint in the space.
Dirty Air Filter
A clogged or dirty air filter will reduce the amount of air blown across the auxiliary electric heater in an air handler and can cause them to over-heat and kick-off on a high temperature limit.
Newer York air handlers have a feature built-into the control board which monitors the number of limit trips.
If the limit switch trips 3 times during a run-cycle, the control board will cause the indoor fan to stay on continuous.
This condition can be reset by turning the air handler power "Off" and then back "On".
Stuck Blower Relay - Qualified Technician Recommended
All furnaces have either a fan relay or a control board to cycle the fan on and off as needed. Sometimes the relay or control can stick which will cause the fan to run continuous.
Heat Pump Failure - Qualified Technician Recommended
We receive multiple service calls every winter where customer reports the problem as their indoor blower running continuous, but the technician arrives to find a heating problem with the heat pump. Heat pumps generally have two stages of heat, the first stage is the outdoor unit and the second stage is back-up (auxiliary heat). If the heat pump is not able to maintain temperature, the thermostat will automatically turn on the auxiliary heat. This will keep the house comfortable, but the thermostat will never satisfy since the 1st stage is not operating correctly, which will appear to be a stuck indoor blower.
Look for "Aux Heat" heat indicators on the thermostat when the unit is heating to determine if the warm air is being produced by 1st or 2nd stage heating.