Compressor Starting Relays and Capacitors) Run Capacitors

 

Examples of Run Capacitors

• Older Style: Single run capacitors with two terminals, often contained PCBs (polychlorinated biphenyls), which were banned in 1979.
• Newer Style: Typically metal and oil-filled, no PCBs, may have three terminals, not polarized, and internally protected.

Run Capacitors in Circuits

• Permanent Split Capacitor (PSC) Motor:
  • Common in split-phase motor arrangements.
  • Run capacitor in series with start winding.
  • No starting relay or start capacitor.
  • Balanced refrigerant pressures required for starting.
• Capacitor Start-Capacitor Run Motor:
  • Includes start capacitor and starting relay (e.g., potential relay).
  • Run capacitor remains in the circuit after the start capacitor is removed.

Function and Benefits

• Phase Shift: Provides a phase shift to start winding for better running efficiency.
• Current Limitation: Limits current to the start winding.
• Running Efficiency: Reduces motor current by up to 20%, improving efficiency.
• Starting Torque: Provides some starting torque, though mainly enhances running efficiency.

Differences Between Start and Run Capacitors

• Color:
  • Start capacitors: Black.
  • Run capacitors: Gray.
• Enclosure and Dielectric:
  • Start capacitors: Plastic enclosure, dry dielectric, designed for short-duration use.
  • Run capacitors: Metal enclosure, oil-filled dielectric, designed to dissipate heat and remain in the circuit.
• Microfarad Ratings:
  • Start capacitors: Higher microfarad values, often a range (e.g., 238-262 µF).
  • Run capacitors: Single microfarad value (e.g., 45 µF).

Dual Run Capacitors

• Purpose: Saves space by combining two capacitors into one.
• Configuration:
  • Three terminals: Common, Fan, Herm (for hermetic compressor).
  • Common terminal for line voltage feed.
  • Fan terminal for condenser fan motor start winding.
  • Herm terminal for compressor start winding.
• Replacement: Replace the entire unit if one capacitor fails.
• Microfarad Values: Two values indicated (e.g., 5 µF for fan motor, 40 µF for compressor).
• Voltage Rating: Should be equal to or greater than the original capacitor.

Replacing Run Capacitors

• Microfarad Rating: Match the exact rating, or within 10% deviation.
• Voltage Rating: Equal to or greater than the original capacitor's rating.

Summary of Run Capacitor Operation

• Starting and Running:
  • Contactors apply line power through the run capacitor to start winding.
  • Limits current, promotes phase shift, improves efficiency, and provides some starting torque.