Use these tips to diagnose problems with a central air conditioning system.

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Causes: Incorrect thermostat setting; no power to unit.

Solutions: Be sure room temperature is above the thermostat setting. Check circuit breakers, main power switch.

Causes: May need refrigerant; airflow problem.

Solutions: Check for a clogged filter or malfunctioning blower. Look for blockages at the condensing unit. Refrigerant must be recharged by a professional.

Causes: May also indicate airflow problems; defective thermostat.

Solutions: Check condenser unit's airflow first, then the filter and blower. Check thermostat.

Causes: If some rooms are too cool and others too warm, duct system needs balancing.

Solutions: To learn about balancing an air system, see Balancing a Forced-Air System, Related Projects. If house doesn't cool sufficiently, the unit may be undersized.