How do I use a hard start kit on a refrigerator compressor?

Installing a hard start kit (commonly known as a 3-in-1 relay/capacitor/overload combo, such as a Supco RCO410 or RCO810) bypasses the refrigerator’s existing start relay, overload protector, and capacitor. It provides a temporary boost in starting torque to free a locked compressor or replace a failing relay assembly.

Note: Hard start kits are designed for standard single-speed Reciprocating/Rotary AC compressors. Do NOT install a 3-in-1 hard start kit on a variable-speed inverter compressor, as doing so will permanently damage the inverter board and compressor.

3-in-1 hard start kit wiring diagram. Source: Facebook

1

Disconnect Power and Discharge the Circuit

Failing to disconnect power creates a severe shock hazard

Unplug the refrigerator from the wall outlet. Remove the lower rear access panel to expose the compressor compartment. If the system has an existing standalone capacitor, discharge it safely by touching an insulated screwdriver across its terminals before touching any wiring.

2

Remove the Original Relay and Overload Assembly

Pull off the plastic cover covering the side of the compressor. Disconnect and completely remove the factory start relay and overload protector from the three compressor terminal pins (C, S, and R). Note the two power feed wires that originally plugged into the old relay assembly.

3

Identify the Compressor Pins

Examine the three bare pins on the compressor housing:

• C (Common)
• S (Start)
• R (Run)

If the pins are unmarked, verify them using resistance measurements with a multimeter (S to R gives the highest resistance, C to R gives the lowest, and C to S gives the intermediate reading).

4

Connect the 3-in-1 Wire Harness to the Pins

Most standard 3-in-1 hard start kits (like Supco) use a standardized color-coded 3-wire harness with female push-on terminals:

• Black Wire: Connect to the Common (C) pin.
• White Wire: Connect to the Start (S) pin.
• Red Wire: Connect to the Run (R) pin.

Always verify the wire color key printed on your specific kit’s packaging before connecting.

5

Connect the Power Supply Wires

Connect the two bare wire leads (or wire nut leads) coming from the hard start kit to the two main power supply wires that previously fed the original relay assembly.

• Hard start power leads are non-polarized (AC current), so either wire from the kit can attach to either incoming power wire.
• Secure the stripped connections tightly using wire nuts and wrap them with electrical tape.

6

Mount the Device and Test Operation

Mount the hard start kit upright using its mounting bracket or zip-ties, ensuring it is secured to the cabinet frame away from hot discharge lines or moving condenser fan blades. Plug the refrigerator back into the wall outlet.

• Success: The compressor should hum briefly and start running smoothly within 1–3 seconds.
• Failure: If the compressor clicks, hums loudly without turning, or trips the circuit breaker, the compressor motor windings are mechanically locked or electrically shorted internally, requiring compressor replacement.