Forced air heating or cooling air handler troubleshooting: blower fan won't shut off: This article describes what to check if the furnace or forced air blower fan does not stop when you expect it to do soThese same diagnostics also aid in air conditioning blower assembly diagnosis when an A/C blower continues running. We explain what switches or controls may be set improperly or what else, such as a shorted wire, can cause continuous HVAC fan operation. First, confirm that the room thermostat is not calling for heating or cooling. In the heating season, just set the thermostat(s) to the lowest setting and confirm that room temperature is above that point. In the cooling season do the opposite - set the thermostat to its highest setting and confirm that room temperature is below that point. You have told the thermostat to turn off the HVAC equipment. If the equipment was running give it three to four minutes to shut down. Next: If the blower just keeps running no matter what, there are two places to check switch settings before calling your heating or air conditioning service company in response to a furnace fan or air conditioning fan that just keeps running without stopping:

1. At the room thermostat: the FAN-AUTO-OFF or FAN ON/OFF switch on the room thermostat should be checked. The fan control should be set to AUTO. You can try turning the switch to OFF too. Details of checking the thermostat's FAN-AUTO-OFF or FAN-ON switch position when the furnace (or air conditioning) fan won't stop running are at FAN WONT STOP - THERMOSTAT SWITCH Other snafus such as a shorted thermostat wire can also cause the A/C or warm air furnace fan to run continuously. Those problems are explained at THERMOSTAT WON'T TURN OFF. 2. At the furnace or air conditioner air handler or blower unit: the FAN LIMIT SWITCH may include a switch that manually keeps the fan running. We discuss this switch here. Take a look at the fan limit control switch. Before pulling the cover off of the switch, just see if the switch includes a control such as the white push-pull switch like the white device shown at the lower left in our photo. Depending on the position of this switch (pushed-in or pulled out) the fan may be on manual override - causing the fan motor to run continuously.

Check the printing on the switch face to see if you should push the switch in or pull it out to leave the blower on "Auto". ("Man" or "Manual" would be forcing the fan to run.) Usually: "Push-in" position on this (Honeywell) fan limit switch is for continuous fan operation and "Pull out" position is for automatic fan operation. There are some reasons (explained at BLOWER FAN CONTINUOUS OPERATION) to leave the blower fan on continuously for long periods, such as to use an air filtering system to improve indoor air quality. And in some buildings we may run the blower continuously for more even or better conditioned (heated or cooled) air distribution. On the off chance that someone has inadvertently mis-connected or shorted fan control wires at the fan limit switch, also check out FAN LIMIT SWITCH INSTALLATION. On the chance that there is a shorted thermostat wire, a problem that can also cause the A/C or warm air furnace fan to run continuously see THERMOSTAT WON'T TURN OFF.

Details about the manual FAN ON or FAN AUTO ON switch right at the furnace or air handler at the manual at BLOWER FAN CONTINUOUS OPERATION. This article series answers most questions about central heating system troubleshooting, inspection, diagnosis, and repairs. We describe how to inspect, troubleshoot and repair heating and air conditioning systems to inform home owners, buyers, and home inspectors of common heating system defects.air handling units calculation Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.ac unit interfering with wifi My fan keeps running with no heat on furnace. where is the air filter on my ac unitWhat can I do?

If the furnace does not even try to run, that is if it never even starts, then follow these steps: If the furnace tries to start but cannot keep running then there is a different problem such as no fuel or an unsafe condition. See DIAGNOSE & FIX HEATING PROBLEMS-FURNACE - home A complete list of oil and gas fired furnace controls is at FURNACE CONTROLS & SWITCHES Continue reading at FAN LIMIT SWITCH or select a topic from the More Reading links or topic ARTICLE INDEX shown below.A/C running constantly, does not shut off when set temp reached. March 9, 2009   SubscribeHome & GardenInteriorsVentilationTroubleshooting Your Central Air Troubleshooting Your Central Air Split-system central air conditioners, used with forced air furnaces, take hot air from the house and blow it through an evaporator coil located in the top of the furnace to cool the air. The cooled air circulates throughout the house via the heat ducts then returns to the furnace as warm air to be cooled again.

Central air conditioners can work for years without problems if properly maintained and serviced annually. If they aren’t working properly, call a trained technician. But before you phone, see if the problem is caused by something else. The unit stops working If you have your system inspected and cleaned annually, it should run without any trouble. However, if it stops working completely and you aren’t sure why, troubleshoot before calling a pro: Check the circuit breaker or fuse box to find out whether the unit has power. Check the fuses in the disconnect box located outside, near the condenser, to make sure there’s power. Replace or clean the furnace filter. If the condenser coils are coated with dust or debris, use a garden hose to wash them off. If the air conditioner still won’t work, make the call. A technician may have to recharge the refrigerant. The unit won’t quit running If the air conditioner runs constantly, here’s what to do:

Turn up the thermostat. If you set the thermostat a few degrees higher, you will save energy and a lot of money when it comes time to pay your electric bill. And your significant other won’t have to complain about wearing a sweater indoors. Take the cover off the condenser and find out whether anything is blocking the air flow. Vacuum the interior of the condenser, and then flush it with a garden hose. If the fan blades are bent or dirty, straighten them out and/or clean them. While the cover is off, oil the motor on older air conditioners. (Newer units are sealed and cannot be oiled.) Take off the plastic covers — there should be two — and put a couple drops of lightweight oil, such as 3-in-1, into each. Check the furnace filter and blower to see whether they’re blocked. Use a vacuum cleaner to clean dust and dirt on or around the blower. Replace the filter if necessary. The unit freezes up If the high pressure lines from the condenser to the furnace or the evaporator coil in the top of the furnace are iced up, then shut the system down: