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AFUE DEFINITION, RATINGS
AGE of AIR CONDITIONERS & HEAT PUMPS
AGE of HEATERS, BOILERS, FURNACES
AIR CONDITIONING & HEAT PUMP SYSTEMS
AIR FILTERS for HVAC SYSTEMS
BACKDRAFTING HEATING EQUIPMENT
BLOWER FAN OPERATION & TESTING
BLUE vs YELLOW COMBUSTION FLAMES
CAPACITORS for HARD STARTING MOTORS
CARBON MONOXIDE - CO
CHIMNEY INSPECTION DIAGNOSIS REPAIR
COOL OFF HEAT, THERMOSTAT SWITCH
CONDENSING BOILERS/FURNACES DAMAGE
CONVECTOR HEATERS - HYDRONIC COILS
DEFINITION of HEATING & COOLING TERMS
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DIAGNOSE & FIX HEATING PROBLEMS-FURNACE
DIAGNOSTIC GUIDES A/C / HEAT PUMP
DRAFT HOOD, GAS HEATER
DRAFT REGULATOR, DAMPER, BOOSTER
DUCT SYSTEM & DUCT DEFECTS
ELECTRIC MOTOR DIAGNOSTIC GUIDE
ELECTRICAL POWER SWITCH FOR HEAT
FAN, AIR HANDLER BLOWER UNIT
FAN AUTO ON THERMOSTAT SWITCH
FAN CONVECTOR HEATERS - HYDRONIC COILS
FAN LIMIT SWITCH
FIRE SAFETY CONTROLS
FLOODED HEATING EQUIPMENT REPAIR
FLUE VENT CONNECTORS
FURNACE CONTROLS & SWITCHES
FURNACE EFFICIENCY, HIGH vs MID
FURNACE OPERATING TEMPERATURES
GAS BURNER FLAME & NOISE DEFECTS
GAS PIPING, VALVES, CONTROLS
GEOTHERMAL HEATING SYSTEMS
HEAT EXCHANGER LEAK TEST
HEAT PUMPS, DIAGNOSIS, REPAIR
HEATING LOSS DIAGNOSIS-FURNACES
HEATING SMALL LOADS
HEATING SYSTEM INSPECT DIAGNOSE REPAIR
HIGH EFFICIENCY BOILERS/FURNACES
GAS LP & NATURAL GAS SAFETY HAZARDS
MANUALS & PARTS GUIDES - HVAC
MOTOR OVERLOAD RESET SWITCH
NO HEAT - FURNACE
NOISE AIR CONDITIONER / HEAT PUMP
NOISE, DUCT VIBRATION DAMPENERS
NOISE, HEATING SYSTEMS
ODORS FROM HEATING SYSTEMS
PULSE COMBUSTION HEATERS
RESET SWITCH - HEAT CONTROL
RESET SWITCH, ELECTRIC MOTOR
RESET SWITCH, STACK RELAY
SAFETY, HEATING INSPECTION
SAFETY RECALLS CHIMNEYS VENTS HEATERS
SPILL SWITCH, FLUE GAS DETECTOR
SPLIT SYSTEM AIR CONDITIONERS & HEAT PUMPS
STAIN DIAGNOSIS on BUILDING INTERIORS
THERMOSTATS, HEATING / COOLING
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 so
. These 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.
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Blower Fan Won't Stop: What to Check if your Furnace Fan Runs Continuously - (the fan won't shut off on its own)
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.
Those problems are explained
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.)
Which way to set the manual furnace or air conditioner blower fan switch:
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
What Else to Check if the Blower or Furnace Fan Won't Stop
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
Details about the manual FAN ON or FAN AUTO ON switch right at the furnace or air handler at the manual
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.
Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.
Continue reading at FAN LIMIT SWITCH or select a topic from the More Reading links shown below.
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