Why does American Standard AC fan run but compressor does not start?

 
Potential Issues with the Start Capacitor
 

• The compressor usually relies on a start capacitor to provide an initial boost of energy. The fan may operate independently while the compressor requires extra torque to crank up. A faulty or degraded capacitor can result in the compressor not receiving adequate starting power, even though the fan continues to run.
• Visual or electrical tests might reveal bulging or leaking capacitor components which indicate that the capacitor is not operating within its specified range.

 

Local experience in St. Louis ensures that issues like these are addressed with expert care.

 

Electrical and Wiring Considerations
 

• The compressor’s control circuitry, wiring, or relay contacts may be compromised. Loose or corroded connections could mean that power is reaching the fan but not the compressor motor, preventing it from starting.
• Inspecting the contactor, relays, and terminal connections in the compressor's wiring compartment can help determine if there is a break or fault in the electrical path leading to the compressor.

 
Overload Protections and Safety Switches
 

• Modern air conditioning systems are equipped with overload protectors and high/low pressure safety switches that disable compressor operation to prevent damage. A nuisance trip or malfunction in these safety devices could be the reason only the fan is operational.
• Monitoring the pressure readings and resetting the overload protection, if necessary, as well as verifying the integrity of the safety switches, can isolate the issue to this area.

 
Compressor Mechanical or Internal Electrical Failure
 

• A worn out compressor motor may fail to begin turning despite receiving some electrical power. Internal issues such as motor winding shorts, mechanical binding, or seized components can inhibit compressor start even though the fan remains unaffected.
• Verification of compressor health might include resistance tests for the motor windings or the use of specialized diagnostic tools to assess mechanical responsiveness.

 
Refrigerant and Pressure Imbalances
 

• If there is an abnormal imbalance in refrigerant charge or system pressures, the system’s safeguards may stop the compressor from engaging. The fan can still operate under these conditions as the control board attempts to mitigate further damage.
• Checking the refrigerant levels and ensuring the system pressures meet manufacturer specifications can reveal if a refrigerant issue is the underlying cause.

 

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