Introduction to Starting Relays
- Starting relays remove the start winding and/or start capacitor from the circuit once the motor reaches the appropriate speed.
- Common issues include the compressor not attempting to start, humming without starting, or running and then tripping on the overload.
Potential Relay
- Normally closed contacts between terminals 1 and 2, wired in series with the start winding and start capacitor.
- Coil between terminals 2 and 5, which opens contacts when energized.
- Test by turning off power, discharging capacitors, and isolating the relay.
- Measure resistance across terminals 1 and 2; zero ohms indicates good contacts, while measurable resistance indicates a fault.
- Coil resistance between 2 and 5 should be measurable, typically between 5,000 to 15,000 ohms.
Current Relay
- Normally open contacts between terminals 1 and S (sometimes L and S) used on smaller compressor motors.
- Test by unplugging the relay and measuring resistance from 1 to S (infinite when upright, zero when inverted).
- Coil resistance between terminal 2 to M or L to M should be less than 2 ohms.
- Visual inspection may reveal corroded or broken connections, common causes of failure.
Testing Relay Function
- If compressor still draws high AMPS and trips overload, test by directly applying voltage to start and run windings.
- Use a switch box for safe testing; if the compressor runs when manually switching off start winding, the relay is faulty.
PTC (Positive Temperature Coefficient) Relays
- Solid-state, thermal devices with no moving parts.
- Wired in series with the start winding; resistance increases as the relay heats up, cutting off current.
- Test by allowing the relay to cool after shutdown; cold resistance should be under 100 ohms.
- High resistance indicates a faulty PTC relay, which needs replacement.
No comments:
Post a Comment