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AIR CONDITIONING & HEAT PUMP SYSTEMS
A/C - HEAT PUMP CONTROLS & SWITCHES
AIR CONDITIONER COMPONENT PARTS
AIR CONDITIONER TYPES, ENERGY SOURCES
AIR FILTER EFFICIENCY
AIR FILTERS, FIBERGLASS PARTICLES
AIR FLOW MEASUREMENT CFM
APPLIANCE DIAGNOSIS & REPAIR
APPLIANCE EFFICIENCY RATINGS
BLOWER DOORS & AIR INFILTRATION
BLOWER FAN CONTINUOUS OPERATION
BLOWER FAN OPERATION & TESTING
BOOKSTORE - Air Conditioning "How To" Books
CAPACITORS for HARD STARTING MOTORS
CLEANING & Legionella BACTERIA
CHINESE DRYWALL HAZARDS
CONDENSATION or SWEATING PIPES, TANKS
DEFINITION of HEATING & COOLING TERMS
DEW POINT CALCULATION for WALLS
DEW POINT TABLE - CONDENSATION POINT GUIDE
DIAGNOSTIC GUIDES A/C / HEAT PUMP
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DIAGNOSE & FIX HEATING PROBLEMS-FURNACE
DUCTS - Asbestos
DUCT INSULATION, Asbestos Paper
DUCT INSULATION for SOUNDPROOFING
DUCT SYSTEM & DUCT DEFECTS
DUCT SYSTEM NOISES
DUCTS, Asbestos Transite Pipe
DUST, HVAC CONTAMINATION STUDY
ELECTRIC MOTOR OVERLOAD RESET SWITCH
EVAPORATIVE COOLING SYSTEMS
FAN LIMIT SWITCH
GAS EXPOSURE EFFECTS, TOXIC
GAS DETECTION INSTRUMENTS
HEAT LOSS (or GAIN) in buildings
HEAT LOSS (or GAIN) INDICATORS
HEAT LOSS R U & K VALUE CALCULATION
HEATING SMALL LOADS
INSPECTION CHECKLIST - OUTDOOR UNIT
INSPECTION LIMITATIONS, A/C SYSTEMS
LEED GREEN BUILDING CERTIFICATION
LOST COOLING CAPACITY
LOW VOLTAGE TRANSFORMER TEST
MOTOR OVERLOAD RESET SWITCH
MOLD in AIR HANDLERS & DUCT WORK
OPERATING COST, AIR CONDITIONER
OPERATING DEFECTS, AIR CONDITIONING
REPAIR GUIDES A/C / HEAT PUMP
REPAIR & DIAGNOSTIC FAQs for A/C
THERMOSTATS, HEATING / COOLING
THERMOSTATIC EXPANSION VALVES
WATER COOLED AIR CONDITIONERS
WINDOW / WALL AIR CONDITIONERS
WINDOW / WALL A/C SUPPORTS
Electric motor thermal overload switch guide: this article describes how to find and reset the thermal overload button on an electric motor and we give suggestions for repairing hard-starting or non-starting electric motors such as on air conditioning condenser fans and blower fans. We describe where to find reset switch on most electric motors. We explain about automatic thermal overload switches on motors - switches that reset themselves when the motor cools down. And we describe what can go wrong with automatic thermal overload switches on electric motors. We include tips for diagnosing electric motors that keep having thermal overload symptoms.
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An electric motor used in lots of equipment may include overload reset button on the motor body. If the motor is overloaded or if it overheats, this button will pop "out" indicating that an internal electric safety device has tripped,shutting the motor off.
Once the motor has cooled sufficiently it can be re-started, usually by pushing the popped-out reset switch back down.
If the motor turns off again on re-set you should not keep running it as it may be damaged and the system may be unsafe.
The page top photo was taken of of an oil burner electric motor not an air conditioning blower fan motor or pump motor, but you'll see that all of these electric motors look a lot alike. Sometimes the reset button on an electric motor is hard to find, and sometimes there is no reset button!. But this photo shows the red reset button most clearly.
Find the electric motor that operates the device that has been shut down. For example on a warm air heating system or central air conditioning system look in the air handler/blower compartment.
On the blower motor itself, look for a red or yellow button which is normally flat with the motor surface but which will pop up to show that the motor has been shut off by its internal overload protection circuit.
If the installer rotated the motor so that the button is facing away from you and impossible to see, feel around on the bottom and back side of the motor for the button's presence. Especially if the motor's internal protection has tripped, it should be easy to feel the button since it'll be sticking up about 1/2".
When the air conditioner fan or blower motor has cooled sufficiently this button can usually be simply pressed back down to "reset" the switch. If the motor overload
switch won't reset (stay depressed) either the motor is still too hot (wait) or there is another failure that needs diagnosis.
Sometimes the reset button is present but hard to find, depending on the position in which the motor was bolted in place.
You can see that in this picture the button is flush with the motor surface. Sometimes these buttons are hard to find but they are usually present on heating and air conditioning system electric motors for fans and blowers.
While manual-reset thermal-overload switches are most common on heating systems such as oil burners and some fan motors, air conditioner electric motors and compressor motors and submersible well pump motors are an example of motor designs that may be use a thermal overload switch that resets itself automatically when the motor has overheated.
If a well pump motor is overheating for any reason (low voltage, bad start/run capacitor, damaged motor, damaged pump impeller parts, loss of water in the well, pump running dry) it may be a model that will turn itself off when too hot. A thermal sensor inside the pump motor housing handles this job. With the motor off for a cool-down period, the thermal sensor automatically resets and the pump will run again. Typically the "off" time is 15-20 minutes. If the pump on-off activity is erratic or very long, it could be that the problem is a bad thermal sensor switch.
General advice: Electrical Tests to Check HVAC Blower Fan Motor or Outdoor Compressor Fan Motor Winding on Heating or Cooling Equipment or on Other Electrical Motors
If your electric motor won't start, vibrates or is noisy, see our diagnostic guide to problems with electric motors at ELECTRIC MOTOR DIAGNOSTIC GUIDE.
If you are looking for the main burner reset button on heating equipment you'll want to see: Aquastat Functions and Cad Cell Relay Switch Flame Sensors (hot water boilers and some water heaters), Stack Relay Switch on older oil fired boilers and furnaces, SPILL SWITCHES (gas fired equipment), and LOW WATER CUTOFF CONTROLS on steam heating systems.
Controls on well pumps and water supply equipment that may require reset or repair are discussed at CONTROLS & SWITCHES on WATER TANKS. And see CAPACITORS for HARD STARTING MOTORS for advice on adding or replacing a start/run capacitor for an electric motor that has trouble starting.
See USING DMMs VOMs SAFELY. Example: testing a blower fan motor winding: referring to the electrical diagram for your equipment, unplug electrical connectors at the fan motor. Measure the resistance between each lead wire with a multimeter or VOM. The multimeter should be set in the X1 range. For accuracy, don't measure when the fan motor is hot, allow it to cool off.
When the resistance between each lead wire are those listed in the specifications for your equipment the fan motor should be normal. Zero resistance or infinite resistance are indicators of a problem.
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