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ELECTRICAL INSPECTION, DIAGNOSIS, REPAIR
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AFCIs ARC FAULT CIRCUIT INTERRUPTERS
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AMPS VOLTS DETERMINATION
AMPACITY - the LIMITING FACTOR
APPLIANCE EFFICIENCY RATINGS
BACKUP ELECTRICAL GENERATORS
BOOKSTORE - ELECTRICAL
BUILDING SAFETY HAZARDS GUIDE
Cadet & Encore Heater Recall
CIRCUIT BREAKER FAILURE
CIRCUIT BREAKER SIZE for A/C or HEAT PUMP
Classified CIRCUIT BREAKER WARNING
CORROSION in ELECTRICAL PANELS
CORROSION & MOISTURE SOURCES in PANELS
CUTLER HAMMER PANEL FIRE
DEFINITIONS of ELECTRICAL TERMS
DIRECTORY OF ELECTRICIANS
DMM Digital Multimeter, How to Use
ELECTRIC METERS & METER BASES
ELECTRIC MOTOR DIAGNOSTIC GUIDE
ELECTRIC MOTOR OVERLOAD RESET SWITCH
ELECTRIC PANEL AMPACITY
ELECTRIC PANEL INSPECTION
ELECTRIC PANEL MOISTURE
Electric Power Frequency Table
EMF RF FIELD & FREQUENCY DEFINITIONS
ELECTRICAL GROUND SYSTEM INSPECTION
ELECTRICAL SERVICE DROP
ELECTRICAL SERVICE ENTRY WIRING
EMF RF FIELD & FREQUENCY DEFINITIONS
FIRE SAFETY Checklist, CPSC
GFCI PROTECTION,Testing GFCIs AFCIs
HEATING COST FUEL & BTU Cost Table
HEAT TAPE USAGE GUIDE
Hertz - Definitions of KHz MHz GHz THz
KNOB & TUBE WIRING
LIGHTING, EXTERIOR GUIDE
LIGHTING, INTERIOR GUIDE
LIGHTNING PROTECTION SYSTEMS
LOW VOLTAGE BUILDING WIRING
LOW VOLTAGE TRANSFORMER TEST
MAIN DISCONNECT AMPACITY
MOISTURE SOURCES in PANELS
MURRAY SIEMENS Recall
PHOTOVOLTAIC POWER SYSTEMS
PUSHMATIC - BULLDOG PANELS
REMOTE ELECTRIC POWER, PHOTOVOLTAIC
RUST in ELECTRICAL PANELS
SAFETY for ELECTRICAL INSPECTORS
SE CABLE SIZES vs AMPS
SIEMENS MURRAY Recall
THERMAL EXPANSION of HOT WATER
THERMAL EXPANSION of MATERIALS
UNDERGROUND SERVICE LATERALS
VOLTS / AMPS MEASUREMENT EQUIP
WIND ENERGY SYSTEMS
WIND TURBINES & LIGHTNING
ZINSCO SYLVANIA ELECTRICAL PANELS
Electric motor test & repair guide: this article describes A/C electrical motor troubleshooting: here we provide an electric motor diagnostic table, a troubleshooting guide that helps diagnose and repair most electric motor problems for motors found on HVAC equipment in buildings such as air conditioners, furnace or air handler blower fans, oil burner motors, well pumps, and condensate return pumps.
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In this article we provide a diagnostic guide to determine and repair problems with electric motors. 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. At left our photo illustrates the motor as typically found in a direct-drive HVAC blower or air handler assembly. (BLOWER FAN OPERATION & TESTING)
While our page top photo shows the red reset button most clearly, the reset button on the motor at left may be harder to spot. Sometimes the reset button on an electric motor is hard to find, and sometimes there is no reset button!
Fatal Shock Hazard Warning: Inspecting electrical components and systems risks death by electrocution as well as serious burns or other injuries to the inspector or to others. Do not attempt these tasks unless you are properly trained and equipped.
What Are the basic Components of an A/C Electric Motor such as used on heating and air conditioning equipment?
Before discussing how to diagnose air conditioner or heating system electric motors let's be sure we know what motor parts might be involved. (Or skip right to Table A if you prefer). The electric motor has quite a few parts if examined in detail, switches, wires, possibly capacitors, oiling ports and more, but there are four basic parts to every HVAC electric motor:
In addition to the basic electric motor components above there are two other features to know about when troubleshooting a motor.
Which way does an Electric Motor Run - Can Electric Motors run Backwards? Information found on the electric motor's data tag.
The two approaches to lubricating the moving parts of an electric motor are:
Permanently-lubricated electric motors: the motor has no oiling ports, has sealed lubricated bearings installed at the factory. Watch out: this motor should not be oiled. Doing so may damage the motor.
Duty-cycle based manually lubricated electric motors: these motors require maintenance according to how much they are in use (their duty cycle) and will have oiling ports, usually an open tube or an openable metal cap at either end of the motor. Here are Beckett's (1989) recommended motor oiling intervals:
Electric Motor Thermal Overload Switch - the Thermal Switch
Details are at ELECTRIC MOTOR OVERLOAD RESET - separate article.
The start switch connects power to the start winding to start the motor spinning. This feature is necessary because depending on the position in which the rotor stopped when the motor last turned off, the rotating electrical field created by the run winding can't start the motor.
A trained service technician may sometimes diagnose a failed start winding or failed start switch by spinning the motor manually (potentially dangerous!). If the motor keeps running we suspect a bad start winding or bad start switch (see diagnostic table details at Table A: 14 Things to Check (in order) if an A/C Electric Motor Will Not Start.
When the electric motor has reached about 80% of its full speed the centrifugal switch opens, thereby disconnecting AC electrical power from the start winding. Power was already connected to and remains connected to the run winding.
So if the motor will start but won't keep running, we suspect a bad run winding or bad wiring to the winding.
For electric motors used in most HVAC applications motor full speed is usually 1725 or 3450 rpm, though some equipment may use variable speed motors as well. The centrifugal switch will open ("throwout") at about 2800 rpm for a 3450 rpm electric motor, and the centrifugal switch will open at about 1400 rpm for a 1725 rpm electric motor.
We've moved this data. Please see separate article: OIL BURNER MOTOR NOISE
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
See these electrical test tool & equipment articles
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.
More examples of procedures checking electrical motor problems & wiring problems
HVAC Repair Article Recommendations
Frequently Asked Questions (FAQs) about how to troubleshoot electrical motors
Question: are there different test procedures for DC electric motors?
This article describes a lot of diagnostic test procedures for A/C electric motors such as those found in air conditioners, heat pumps, washing machines, clothes dryers, condensate pumps, well pumps, even garage door openers. But what about direct current motors such as used by hobbyists and in some automotive or boat applications?
Hobbyist LB Miller has described the design and function of a simple test fixture useful for determining the electrical resistance of DC motors by providing a 1A current to the motor and measuring the voltage drop across the motor, thus giving motor resistance in milli-ohms. Note that his approach is for DC motors. 
Questions & answers or comments about how to troubleshoot electric motors such as air conditioning compressor motors, heating equipment burner or fan motors, swimming pool motors, water well pump motors
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