Compressor Starting Relays and Capacitors) Start Capacitor

 

Purpose of Start Capacitors

• Increase Starting Torque: Helps motors start under high head pressure.
• Applications: Systems with thermostatic expansion valves where refrigerant pressures don't equalize during the off cycle.

Circuit Configuration

• Wiring: In series with starting relay contacts and start winding.
• Operation:
  • Starting relay energizes, breaking power to start winding and start capacitor.
  • Start capacitor only remains in the circuit for 1-2 seconds to avoid overheating.

Phase Shift and Starting Torque

• Function: Increases phase shift in windings, enhancing starting torque.
• Discharge: Bleed resistors (15k-20k ohms) discharge excess charge during the off cycle, preventing contact damage.

Safety and Replacement

• Discharging Capacitors:
  • Use proper capacitor discharge tools.
  • Bleed resistors help, but always ensure capacitor is fully discharged.
• Checking Capacitors: Remove bleed resistor for accurate readings with ohm or microfarad meters, then reattach.
• Replacement Criteria:
  • Same microfarad (µF) value as original.
  • Voltage rating equal to or greater than original.
  • Example: Capacitors with the same µF but different voltage ratings (125V, 250V, 330V).

Symbols and Ratings

• Microfarads (µF): Unit of capacitance.
• Voltage Rating: Maximum voltage capacitor can handle based on insulating material.
• Example:
  • Capacitors with 145-175 µF ratings but different voltage ratings.
  • A capacitor with a higher voltage rating can replace one with a lower rating if the µF value matches.