Compressor malfunctions are typically caused by faulty electrical connections, defective capacitors, and improper refrigerant levels that affect the system's operating pressure. Before calling a professional, homeowners can replace the air filter, double-check the thermostat settings, and hose off the outdoor unit to rule out minor maintenance-related problems. If these steps don't resolve the issue, the compressor may need to be replaced. Unfortunately, compressors aren't just one of the most critical components of the air conditioning system, they're also one of the most expensive. If the unit can't be repaired, a licensed HVAC contractor can determine whether a partial or full replacement is the best option.