Central AC Tune-Up Guide

The air filter is your AC's first line of defense and the easiest maintenance task. Locate the filter slot at the air handler (indoor unit) or in a return grille. Remove the old filter and hold it up to a light—if you cannot see light through it, replace it. Choose a filter with a MERV rating between 8 and 13. Higher MERV ratings trap more particles but also restrict airflow—check your system manual for the maximum recommended rating. Insert the new filter with the airflow arrow pointing toward the furnace or air handler. Write the date on the filter frame. Set a calendar reminder to check the filter monthly. During peak summer, filters may need replacement every 4–6 weeks. A clean filter keeps the evaporator coil clean and maximizes cooling capacity.

The outdoor condensing unit needs clearance and cleanliness to reject heat efficiently. Turn off power at the breaker and the disconnect switch. Remove leaves, grass clippings, and debris from the sides and top of the unit. Use a vacuum with a brush attachment to clean the coil fins. If fins are matted, apply foaming coil cleaner and rinse gently with a hose—never use a pressure washer within 18 inches. Straighten bent fins with a fin comb. Verify the unit is level on its concrete pad. Trim vegetation around the unit—maintain at least 2 feet of clearance on all sides and 5 feet above. Check that the refrigerant lines entering the house are insulated and the insulation is intact. Replace damaged line insulation with foam pipe wrap.

Inspect the electrical disconnect and contactor for signs of overheating. With power off, check the capacitor for bulging or leaking—these signs mean immediate replacement needed. Test the capacitor with a multimeter set to capacitance mode; replace if it reads more than 5% below rated value. Check the contactor contacts for pitting or burning. Inspect all wiring for cracked insulation or loose connections. Tighten terminal screws to manufacturer torque specifications. Check the fan blade for cracks and verify it spins freely. Plug the disconnect back in and turn on the breaker. Start the system and verify the fan starts smoothly. Check the amp draw on the compressor and fan against the nameplate ratings. High amp draw indicates a failing motor or compressor.

After the system has run for 15 minutes, measure the temperature at the supply vent closest to the air handler and at the return grille. The difference should be 14–20 degrees for a properly functioning system. A smaller difference indicates low refrigerant, restricted airflow, or a failing compressor. Check all supply vents in each room—airflow should be strong and even. Weak airflow in one room may indicate a duct issue or a closed balancing damper. Listen for unusual sounds: clicking (relay issues), hissing (refrigerant leak), squealing (blower belt or bearing), or rattling (loose components). Check the condensate drain line—it should be dripping steadily during operation. If it is dry, the drain may be clogged, which can cause water damage.