The start relay serves as a crucial component in the compressor starting circuit
The start relay serves as a crucial component in the compressor starting circuit, providing the electrical switching necessary to energize the compressor's start winding during motor startup. Single-phase compressor motors require additional starting torque to overcome initial inertia and begin rotation. The start relay accomplishes this by temporarily connecting a start winding in parallel with the main running winding, creating the phase shift needed for starting torque generation. Once the compressor reaches approximately 75% of running speed, the relay automatically disconnects the start winding, allowing the motor to continue running efficiently on the main winding alone.
Most refrigerator start relays operate using either electromagnetic or thermostatic principles. Electromagnetic relays, also called voltage relays or current relays, use the back-EMF (electromotive force) generated by the running winding to operate a switching mechanism. As the compressor motor accelerates, the increasing back-EMF creates sufficient magnetic force to open relay contacts and disconnect the start winding. Thermostatic relays, also known as PTC (Positive Temperature Coefficient) relays, use a temperature-sensitive resistor that increases resistance as it heats up, effectively limiting current flow to the start winding after initial startup.
The start relay works in conjunction with an overload protector to provide complete compressor protection. While the overload protector guards against overcurrent conditions, the start relay ensures proper starting sequence timing. Modern start relays are designed to handle multiple start attempts and provide consistent operation throughout the compressor's service life, contributing significantly to overall refrigerator reliability and energy efficiency.
Symptoms of a Broken Start Relay
A failing start relay typically manifests through compressor starting problems that can range from intermittent operation to complete failure. The most common symptom is a compressor that attempts to start but immediately shuts down, often accompanied by a clicking sound as the overload protector trips. This clicking may repeat every few minutes as the system attempts to restart, but the compressor never actually begins running normally.
You may notice that the refrigerator occasionally starts and runs normally, but fails to start during other attempts, indicating an intermittent relay failure. Temperature control becomes erratic as the cooling system operates unpredictably. The compressor may make unusual humming or buzzing sounds as it receives power but cannot develop sufficient starting torque due to improper start winding energization.
In some cases, a completely failed start relay prevents any compressor operation, leaving the refrigerator entirely without cooling. The unit may appear to have power, with lights and controls functioning normally, but no compressor activity occurs regardless of temperature settings. Advanced relay failures might cause continuous start winding energization, leading to rapid overload protector tripping and potential compressor motor damage if not addressed promptly.
Repair Solutions
Diagnosing start relay problems requires careful testing to distinguish relay failures from other compressor circuit issues. Begin by unplugging the refrigerator and locating the start relay, typically found plugged into terminals on the compressor housing or mounted nearby on the compressor compartment wall. The relay is usually a small rectangular or cylindrical component with two or three terminals.
Remove the start relay from its mounting position and inspect it visually for obvious damage such as cracked housing, burned terminals, or signs of overheating. Shake the relay gently; rattling sounds may indicate broken internal components in electromagnetic relays. For PTC thermostatic relays, check for any visible cracks or discoloration that might indicate thermal damage.
Test the relay using a multimeter set to resistance mode. For electromagnetic relays, check continuity between relay terminals with the relay in different positions. Terminal resistance should change when the relay is tilted or rotated, indicating proper contact movement. PTC relays should show low resistance when cool and higher resistance when warmed, demonstrating proper thermostatic operation.
The most definitive test involves substituting a known good relay of the same type and specifications. If the compressor starts and runs normally with a replacement relay, the original relay is definitely faulty. When purchasing a replacement relay, use the exact part number from the original relay or consult the refrigerator's service manual for compatible alternatives.
Installation of a new start relay is straightforward but requires attention to proper terminal connections. Ensure the relay terminals align correctly with the compressor terminal arrangement, typically marked as C (common), S (start), and R (run). Push the relay firmly onto the terminals until it seats completely, then reinstall any mounting brackets or clips. After installation, test the compressor operation through several start-stop cycles to verify proper relay function and confirm that the cooling system operates normally.