Starting capacitors in place on an air conditioning compressor (C) InspectAPedia.comElectric Motor Start / Run Capacitor Location
Guide to the Proper Placement or Location of Electric Motor Start-Boost or Run Capacitors

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Motor capacitor location: how to find & recognize the electric start, run, or hard starting capacitor on an air conditioner or heat pump system. This air conditioning, heat pump, or other electric motor repair article series discusses the selection, installation, testing, & use of electric motor starter start and run capacitors designed to get a hard-starting air conditioner compressor motor, fan motor, refrigerator, or freezer compressor or other electric motor (such as a well pump) going.

This electric motor capacitor article series explains the selection, installation, testing, & use of electric motor starter start and run capacitors used on various electric motors found in or at buildings such as air conditioner compressors, fan motors, some well pumps and some heating equipment.

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How & Where to Find or Locate the Starter Capacitor in or on Electrical Equipment

Starting capacitors in place on an air conditioning compressor (C) InspectAPedia.comLook for starter capacitors in your air conditioning equipment in the outside air handler where a starter capacitor may be used to aid compressor motor start-up, and look for a smaller motor starting capacitor on fan motors, both

  • in the outside compressor/condenser and
  • indoors in the air handler unit's blower compartment.

A three-phase electric motor typically won't have a starter capacitor, but you won't find many residential cooling systems wired for 3-phase current. You also won't see a starter capacitor on scroll-type refrigeration compressor motors.

In our photo of a rather messy wiring job at left you can see two separate capacitors marked by the blue and red arrows.

Also see MOTOR CAPACITOR TYPES for help in determining which capacitor is which on your HVAC or other electrical equipment.

Start & Run & Dual Capacitor Specification References

  • Essex, Brown: "Motor Repair Supplies" (Catalog), Essex Group, Inc., 1601 Wall St., Fort Wayne, Indiana 46801, Tel: 219-461-4633, Website:, retrieved 6/20/14, original source: - see pp. 86-89.
  • Sealed Unit Parts Co., Inc., PO Box 21, 2230 Landmark Place, Allenwood NJ 08720, USA, Tel: 732-223-6644, Website:, Email: info@supcocom, Supco Catalog, retrieved 6/20/14, original source: - see pp. 2-6.
  • van Roon, Tony, "Capacitors", [online article], retrieved 6/20/14, original source:, gives a very detailed history of the invention and history of electrical capcitors beginning with van Musschenbroek's Leyden jar in 1745. This article includes
    "Capacitor Nomenclature" by Dean Huster.
  • Kaiser, Cletus J., The Capacitor Handbook: A Comprehensive Guide For Correct Component Selection In All Circuit Applications. Know What To Use When And Where, 2d Ed., [at] C.J. Publishing (2011), ISBN-10: 0962852538, ISBN-13: 978-0962852534 - product description
    This book provides practical guidance and application information when using capacitors in electronics and electrical circuit design. This easy-to-use book covers the following capacitor types: Ceramic, Plastic Film, Aluminum Electrolytic, Tantalum, Glass, Mica, and others. This book also has a very comprehensive Glossary and Index. The Selection Guidelines and the Symbols and Equations sections have the answers to all of your daily application questions. This book is one in a series of component handbooks.

Examples & Sources of Start / Run Motor Capacitors

  • Packard 370V 45+5 MFD Round Run Capacitor
  • Supco™ 30+5 MFD 440V 440 Volt 50/60 Hz Round Motor Capacitor (typical application for Amana, Carrier, Rheem, Trane equipment)
  • Supco™ 45+5 MFD 440V 440 Vol 50/60 Hz Round Motor Capacitor (typical application for Amana, Carrier, Rheem, Trane equipment)
  • Supco HS6 (SPP6) Hard Start Relay Capacitor (230V) gives a starting torque boost of up to 500%. Quoting from product sales literature:
    The SUPCO SPP6 Super Boost hard start capacitor increases starting torque up to 500%. Features: Installs in seconds across run capacitor terminals Contains specially designed relay and large start capacitor for severe hard start problems. Applications: Room A/C units, Residential and commercial PSC A/C units and heat pumps, For all PSC A/C units from 4,000 thru 120,000 BTU's (1/2 thru 10 H.P.) Can be used on 120 thru 288 VAC units, For severe low voltage and hard starting compressors. SPP6 Specifications: Voltage: 115V - 230V. Increased Torque: 390 ounce inches. - retrieved 6/16/14 sales
  • Supco™ Universal (broad application) Capacitor, 10 MFD at 370V


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