How to Diagnose & Repair Electric Motors on Building Equipment
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Electric Motor Troubleshooting Guide - Diagnostic Table
Electric motor troubleshooting guide for electric motors that won't start
Electric motor troubleshooting guide for electric motors that overheat
Equipment 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, blower fans, well pumps, and condensate return pumps.
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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. We provide a diagnostic guide to problems with electric motors here.
Thermal overload relays on electric motors used on air conditioning, heating, water supply and other building equipment may shut off an overheated motor and (if not automatic) may require a manual reset. See ELECTRIC MOTOR OVERLOAD RESET SWITCH explanation (how to reset a motor off on reset).
Water supply systems: Controls on well pumps and water supply equipment that may require reset or repair are discussed at CONTROLS & SWITCHES on WATER TANKS.
Some of the electric motor troubleshooting suggestions in this list can be found at the Betta-Flo Jet Pump Installation Manual from the National Pump Co.
Things to Check if an Electric Motor Will Not Start
Using a well pump motor as an example, most of these troubleshooting tips pertain to other electric motor applications in buildings too such as in an air conditioning air handler blower compartment
Motor Trouble Cause
Diagnostic Procedure
Repair Procedure
Electrical Power is Off
Check that all service switches for the equipment are in the "on" position.
Check for voltage at the pump motor or pump controls. If no voltage is found, check for voltage at the electric panel.
If power is on to the building, check fuse or circuit breaker serving the electric motor that won't run.
Check for local reset button on the motor (popped out = off )
Check for other power reset or power off buttons such as an access door compartment safety switch that turns off power to the equipment (found on A/C blower compartment doors)
Turn on "off" switches.
Replace bad fuse. Reset circuit breaker; if necessary replace bad circuit breaker.
Let hot electric motor cool down, then push in its reset button.
Be sure all safety interlock switches such as on compartment doors are depressed and that the doors are securely shut. Replace a bad safety switch.
Ambient temperature may be too high, or other failure conditions (defective control switch, loss of well water) can cause the motor to run too long leading to overheating.
Some motors such as submersible pumps include an automatic self-reset once the motor cools down. Other motors use a manual button that must be reset. See ELECTRIC MOTOR OVERLOAD RESET SWITCH for how to find and reset this button.
Check with VOM at the pressure control switch or at the motor wiring. Incorrect voltage can prevent motors from starting or may cause slow "weak" electric motor operation.
Be sure the proper size of wire is used for the ampacity and length of circuit; Test for low voltage to the building.
Loose, improper, or broken motor wire
Check wiring against the motor installation manual diagram, check all connections for tightness, shorts, burns, damage
Rewire or repair or replace wiring
Bad motor control switch
Check the control switch contacts for burning or wear.
If the motor control is a well pump pressure control switch,check the pressure control switch settings - cut-in and cut-out; inspect for burned, pitted switch contacts or for dirt or wear.
For water pumps, adjust or replace the pressure control switch.
Clogged or leaky tubing connecting a water pump pressure control switch to the water system results in failure to properly sense and respond to water pressure.
Debris clogging can also occur in the bottom of the pressure control switch where it mounts or connects to the tubing.
Check and clear tubing blockage (blow air through tubing). Or install new tubing.
Be sure tubing is proper diameter and type to seal properly with other fittings.
Tighten tubing fittings to be sure there are no water or air leaks. Soap solution may help find air leaks in tubing fittings.
Clear or replace clogged pressure control switch if the bottom sensor opening is clogged and cannot be cleared.
Bad mechanical parts being turned by the motor - e.g. blower assembly or well water pump impeller
Turn off electric power to motor, see if you can move the impeller or blower assembly or motor shaft - if it won't turn it is jammed or damaged
Remove obstruction in mechanical components, inspect for and replace damaged parts or a frozen electric motor itself
Bad electric motor starting capacitor
Use a VOM in ohms setting to check resistance across the capacitor. If the meter does not move (no current flows) the capacitor is "open". If there is zero resistance the capacitor is shorted.
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, operating conditions
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.
Operating conditions can cause a motor to overheat, such as a well pump that runs continually because of other problems in the water system
Install adequate ventilation, or if needed, shading, or relocate the motor/equipment to a cool location
Look for abnormal conditions that cause the motor to keep running (bad control, loss of well water, bad pump controls, water left running in the building, valve closed on pump outlet side, strainer clogged at pump inlet or outlet, pump running continually due to improper voltage, pump running backwards due to electrical damage or mis-wiring or starter capacitor short)
A well pump motor may run continually and be unable to reach shut-off pressure due to a damaged impeller or loss of well water.
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
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 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.
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Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.
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
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop. The Home Reference Book 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. InspectAPedia.com ® author/editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.
"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]
Carson Dunlop, Associates, Toronto, have provided us with (and we recommend)
Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment ($69.00 U.S.).
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