Air Conditioning Starting Relays.

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Presentation transcript:

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

These are the three most common 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.

Three types Current Coil Relay Solid State Relay or PTC Potential Relay

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

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

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

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

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…)

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.

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

Operates from voltage created by start winding Also known as 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

All other terminals are blanks 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

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