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DEFINITION of Heating & Cooling Terms
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ELECTRIC MOTOR OVERLOAD RESET SWITCH
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REPAIR GUIDE, AIR CONDITIONERS / HEAT PUMPS
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More Information

Photograph of the overload reset button on an electric motor Electric Motor Reset Button
How to Reset the Thermal Overload Switch on Electric motors

     

  • RESET BUTTON, ELECTRIC MOTOR - How to find and reset the thermal overload switch found on many electric motors
    • Tips for Finding the Motor Reset Button
    • How to reset the motor switch on a furnace or air conditioner blower fan unit
    • What the Reset Button Looks Like When it has Not Tripped
    • Some Electric Motors Include an Automatic Thermal Reset Switch How to reset the motor switch on water pumps and well pumps
    • Electric motor troubleshooting guide for electric motors that overheat
  • AMPS MEASUREMENT METHODS - separate article
  • BURNED-OUT COMPRESSOR - separate article
  • CAPACITORS for HARD STARTING MOTORS - separate article
  • ELECTRIC MOTOR DIAGNOSTIC GUIDE - separate article
  • HARD STARTING COMPRESSOR MOTORS - separate article
  • Test a Motor Starting Capacitor - separate article
  • TIGHT or SEIZED AC COMPRESSORS - separate article
  • Questions & answers on electric motor problems, motor overheating, thermal overload protection devices
  • References

Click to Show or Hide Related Topics

  • AIR CONDITIONING & HEAT PUMP SYSTEMS - home
  • AMPS MEASUREMENT METHODS
  • AMPS VOLTS DETERMINATION
  • BURNED-OUT COMPRESSOR
  • CAPACITORS for HARD STARTING MOTORS
  • CIRCUIT BREAKER SIZE for A/C or HEAT PUMP
  • COMPRESSOR & CONDENSING COIL, A/C
  • CONTROLS & SWITCHES, A/C - HEAT PUMP
  • DATA TAGS on AIR CONDITIONERS
  • DMM Digital Multimeter, HOW TO USE
  • DMM & VOM SAFETY
  • ELECTRIC MOTOR DIAGNOSTIC GUIDE
  • ELECTRIC MOTOR OVERLOAD RESET
  • ELECTRICAL BASICS
  • ELECTRICAL INSPECTION, DIAGNOSIS, REPAIR - home
  • ELECTRICAL TOOLS BASIC
  • ELECTRICAL WIRING COLOR CODES
  • EXPANSION VALVES, REFRIGERANT
  • FAN, AIR HANDLER BLOWER UNIT
  • FAN AUTO ON Thermostat Switch
  • FAN, COMPRESSOR/CONDENSER UNIT
  • HARD STARTING COMPRESSOR MOTORS
  • HEAT PUMPS
  • HEATING SYSTEMS
  • MANUALS & PARTS GUIDES - HVAC
  • NOISE AIR CONDITIONER / HEAT PUMP
  • ODORS in AIR HANDLERS & DUCT WORK
  • OIL BURNER MOTOR NOISE
  • REPAIR GUIDE - A/C or Heat Pumps
  • RESET SWITCH - ELECTRIC MOTOR
  • TEST EQUIPMENT, ELECTRICAL GUIDE
  • THERMOSTATS, HEATING / COOLING
  • WATER PUMP REPAIR GUIDE - home
  • WATER PUMP PROBLEM DIAGNOSTIC TABLE
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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.

Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.

How to Find and Reset a Heating System or Air Conditioning Electric Motor

Electric motor overload reset buttons - how to find and reset motor overload switches

Photograph of the overload reset button on an electric motor
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.

Tips for Finding the Motor Reset Button

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 and How to Reset the Electric Motor on a Heating Blower, Air Conditioner Blower, or Water Pump

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.

What the Reset Button Looks Like When it has Not Tripped

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.

Electric Motors Using an Automatic Thermal Reset Switch - no reset button found

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.

Electric Motor Thermal Overload Switch Trip Temperatures

Class A electric motor 140oC / 284oF
Class B electric motor 165oC / 329oF
The reset temperature is not precisely specified but the automatic thermal overload switch will reset after the motor cools down. [1]

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.

Note that other electric motors may have a thermal reset switch that is mechanical and "pops out" to show a red "reset button" that must be pushed back in manually. If the motor is still too hot, pushing the button won't work - the button won't stay in.

Electric Motor Reset Switch Troubleshooting Guide

Table of Causes of Electric Motor Thermal Overload Switch-Off

Things to Check if an Electric Motor Starts but Overheats and Trips its Reset Button

This first table is for electric motors use in air conditioners, air handlers, blower units, oil burners on boilers, steam boilers, water heaters etc. - HVAC equpment in general. A second section of defects (below) addresses oil burner motors.
Bad line voltage Use a VOM to check the voltage level at the pressure control switch If voltage is too low, check voltage at the electrical panel and check that the proper size wiring was used for the ampacity and length of run and that there are no partial shorts or damaged wires or connectors
Incorrect motor wiring Check the actual electrical wiring against the motor wiring diagram or the installation manual for the equipment Reconnect wiring properly
Motor is too hot due to surroundings - inadequate ventilation Check the air temperature where the motor is located. If the air temperature is over 100 degF, the pump may be too hot and its thermal overload switch tripping because of the environment, not a pump problem. Install adequate ventilation, or if needed, shading, or relocate the motor/equipment to a cool location
Motor subjected to repeated overloading, overheating A motor subjected to overloading due to very long duty on-cycles may run hot and trip the thermal overload protection device. Eventually the thermal overload switch may itself fail and the motor will no longer restart nor can you reset the thermal overload switch. Check the recommended duty cycle and loading on your motor; check also for abnormally low voltage levels in the electrical supply. If necessary, replace the motor with a heavier-duty unit.
Motor for a water pump operates too long at low water pressure If the well recovery rate is too poor and the pump is operating at low water pressure, possibly because a tailpiece is installed to prevent air injection and pump burnup, the pump may be overheating. Install a valve on the water discharge line and reduce water flow to increase water pressure inside the pump itself. See WATER PRESSURE PROBLEM DIAGNOSIS TABLE

Adapted from various sources incuding Betta-Flo Jet Pump Installation Manual from the National Pump Co. and Adapted & expanded from Beckett (1989)[1]


Table of Causes of Oil Burner Thermal Overload Switch-Off

Bad oil pump (fuel unit) Oil pump has seized or is binding, overloading the electric motor Disconnect the coupling between fuel unit and electric motor and manually turn each shaft to inspect for binding or seizure. Replace a bad fuel unit.
Misaligned components Connections between the electric motor drive shaft, coupling, and driven parts are loose or improperly mounted Check for misalighment due to loose mounting bolts of motor, blower, fuel unit; check for improper seating of the motor against the oil burner housing such that the motor is askew. Re-mount.
Bad electric motor start switch The electric motor will overheat if the start-switch does not disconnect at the proper or "throwout" rpm. See Electric motor start switch operation
Jammed blower wheel If the oil burner air blower wheel has jammed, possibly due to debris, mechanical damage, obstruction, the motor may spin the coupling or may not rotate at all, overheating & shutting down Inspect the blower assembly for obstruction, free spinning, and repair
Undersized electric motor Load requirements exceed the motor horsepower Hp nameplate ratings. [Unlikely on factory-assembled heating or air conditioning system but possible if someone performing a repair substituted a lower Hp motor].

Using an Amp probe ammeter check the current draw of the motor against its nameplate rating. If the actual current draw when the motor is running exceeds the rated run-amps by more than 10% and if there is no binding or misalighment in the system we suspect that the motor is under-sized.

See TEST EQUIPMENT, ELECTRICAL GUIDE - separate article

Bad coupling Jammed or defective coupling between motor and driven components; improper belt tensioning on belt-driven compnents Usually a bad coupling inside the oil burner will fail by becoming loose and just spinning, so the motor runs but the driven components do not spin or spin at a too-low speed. But a bent, damaged, or jammed coupling might overheat a motor - OPINION - Ed.
Electric Motor Lubrication Failure If the electric motor is a model that requires periodic lubrication and is not properly maintained its drive shaft or bearings may run dry, causing binding and overheating.

Inspect the motor to determine if it is a model that requires lubrication. Check its maintenance history; check for shaft binding; lubricate the motor if appropriate; check motor drive shaft and bearings for excessive side play, wear, or looseness.

Watch out: do not try to lubricate an electric motor that does not have lubrication fittings.

Details are at Electric Motor Lubrication Specifications

Adapted & expanded from Beckett (1989)[1]

Also see ELECTRIC MOTOR DIAGNOSTIC GUIDE - separate article

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.


Frequently Asked Questions (FAQs) about the reset button on electric motors

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Questions & answers on electric motor problems, motor overheating, thermal overload protection devices

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Technical Reviewers & References

Related Topics, found near the top of this page suggest articles closely related to this one.

Click to Show or Hide Citations & References

  • [1] Beckett Oil Burners, "Burner Motor Service Facts", Beckett Corporation, Technical Information, 15 June 1989 [copy on file as PDF].
  • [2] N. Srinivasan, MSEE, is a senior member of IEEE with 30 years experience in the electrical industry. Mr. Srinivasan is in Vienna VA.
  • [3] Louis P. Babin generously contributed technical editing about the effects of doubling ampacity in an electrical circuit (September 2007)
  • [4] Digisnap DSA-500 snap-around digital multimeter, A.W. Sperry Instruments Inc., 2150 Joshua's Path, Suite 202, Hauppage NY 11788, Tel: 800-645-5398, Email: cat@awsperry.com, Website: www.awsperry.com
  • [5] Fluke Corporation, 6920 Seaway Blvd, Everett, WA 98203, USA, PO Box 9090 Everett, Washington 98206, Tel: +1(425) 347-6100, Technical support: 1(800) 44-FLUKE (1(800) 443-5853), Website: www.fluke.com,
    Fluke Europe B.V, PO Box 1186 Eindhoven, The Netherlands, Tel: +31 (0)40 2 675 200 +31 (0)40 2 675 222, Website: www.fluke.eu
  • [6] Simpson Electric, P.O. Box 99, 520 Simpson Avenue, Lac du Flambeau, WI 54538-0099 Tel: 715-588-3311, customer service: 715-588-3947, Email: support@simpsonelectric.com, Website: www.simpsonelectric.com/
  • [7] tif 300cc Tic Tracer voltage detector, Tif Instruments Inc., 9101 NW 7th Avenue, Miami, Florida 33150
  • [8] Greenlee® GT-16 adjustable voltage detector, Greenlee Textron Inc., Website: greenlee.com, Tel: 800-435-0786 , Email: echsupport@greenlee.textron.com,
  • [9] Jensen VOMs, no longer available
  • [10] Mastech VOMs and DMMs (made in China), Shanghai Hihua V&A Instrument Company, 881 Ye Cheng Road Jia Ding District, Shanghai 201821, China, Email: mastech@vip.sina.com, Tel: +86 21 69523164 +86 21 69523225, Website: http://www.mastech.com.cn/
  • [11] Equus Multimeters by Innova, Equus Products, Inc., 17352 Von Karman Ave., Irvine, CA 92614, U.S.A., Tel: 714-241-6800, Website: http://www.equus.com/
  • [12] Actron DMMs & VOMs, Website: http://www.actron.com/
  • [13] ExTech DMMs & VOMs, ExTech Corp. a FLIR company, Extech Instruments Corporation, 9 Townsend West, Nashua, NH 03063, U.S.A., Email: support@extech.com, Tel: 877-239-8324 Option 3, Website: http://www.extech.com
  • [14] Typical Deep Well Two Line Jet Pump Installation, Grove Electric, G&G Electric & Plumbing, 1900 NE 78th St., Suite 101, Vancouver WA 98665 www.grovelectric.com - web search -7/15/2010 original source: http://www.groverelectric.com/howto/38_Typical%20Jet%20Pump%20Installation.pdf
  • Modern Refrigeration and Air Conditioning, A. D. Althouse, C.H. Turnquist, A. Bracciano, Goodheart-Willcox Co., 1982
  • Principles of Refrigeration, R. Warren Marsh, C. Thomas Olivo, Delmar Publishers, 1979
  • "Air Conditioning & Refrigeration I & II", BOCES Education, Warren Hilliard (instructor), Poughkeepsie, New York, May - July 1982, [classroom notes from air conditioning and refrigeration maintenance and repair course attended by the website author]
  • Refrigeration and Air Conditioning Technology, 5th Ed., William C. Whitman, William M. Johnson, John Tomczyk, Cengage Learning, 2005, ISBN 1401837654, 9781401837655 1324 pages
  • ...

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  • Home Reference Book - Carson DunlopThe Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

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