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Air Conditioning

Air Conditioning. Starting Relays. Starting Relays. Purpose Remove the start winding and/or start capacitor from the circuit Compressor start relays are mounted outside the motor Centrifugal switch could not be used in hermetic motor. Types of Relays. These are the three most common

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Air Conditioning

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  1. Air Conditioning Starting Relays

  2. Starting Relays Purpose • Remove the start winding and/or start capacitor from the circuit • Compressor start relays are mounted outside the motor • Centrifugal switch could not be used in hermetic motor

  3. Types of Relays • These are the three most common • The HP of the motor will determine what type will be used • Service man may replace not re-design.

  4. Three types • Current Coil Relay • Solid State Relay or PTC • Potential Relay

  5. Current Coil Relay • Works off amperage to the run winding. • On compressor start up: • Motor draws high current • Induces a strong magnetic field in the relay’s magnetic coil through the run winding • This magnetic field lifts a plunger with contacts and a counter tension spring • Contacts to start winding are made • Start winding is energized

  6. Motor now starts because start winding creates a strong magnetic field • Motor reaches 75% running capability: • Current drops down • Relay coil is in series with run winding • Not enough current remains to keep coil magnetized • Spring pushes plunger down • START WINDING IS DE-ENERGIZED

  7. Used mainly on fractional horsepower compressors for small refrigeration units, not A/C

  8. Solid State Relay • Also works off current • Has materials that changes its resistance • PTC-Positive Temperature Coefficient • Temp goes up/ resistance goes up • Wired in series with start winding only

  9. Uses up voltage (loads in series) • Example: • Voltage drop across relay would be 110v • Voltage drop across start winding 10v • REMEMBER series law (Et=E1+E2…)

  10. Solid State relays have a greater range • Example: 1 SS relay may be used for • 1/16 to 3/4 Hp motor • 3/4 to 2 HP motor • If a current coil was used different relays would be needed.

  11. Types of Solid State relays • Two wire is relay only • Five wire is start capacitor, relay and overload • Testing: • When Ohmming them out, a good relay will have a (low) resistance reading • Must cool down before testing

  12. Potential Relay • Operates from voltage created by start winding • Also known as • Back Electromotive Force, or Back EMF • Operation • Contacts are N.C. and allow full voltage to start winding

  13. Terminals that are used and how to wire potential relay (this is the ONLY way) • Line to start capacitor • Start capacitor to TERM #1 • TERM #2 to start winding • TERM #5 to common terminal • All other terminals are blanks

  14. Checking the Potential relay with Ohmmeter • Term #1 to Term #2 • Continuity • Term #1 to Term #5 • Ohm Reading • Ex. 2k ohms • The same for Term #2 to Term #5

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