Why Is My Heat Pump Not Cooling on Hot Days?

A heat pump that won’t cool on hot days usually has an airflow restriction, thermostat setting error, or a refrigerant problem. The most common culprit is poor airflow from a clogged filter or a blocked outdoor coil, which causes weak cooling and long run times. Other possibilities include low refrigerant from a leak, a frozen indoor coil after extended cooling cycles, or a unit that’s undersized for peak heat. Our technicians serving the Indianapolis area often find outdoor coils packed with cottonwood fluff that looks clean until you remove the top panel. If basic checks don’t restore cooling, schedule a repair; persistent struggles on every heat wave may signal it’s time to evaluate system size or replacement.

Try these quick checks before calling:

• Replace the air filter and open all supply/return vents.
• Clear 2 feet around the outdoor unit and gently rinse the coil fins.
• Confirm thermostat is set to Cool, Fan on Auto, and temperature lower than room.
• Look for ice on lines or coil; if present, shut cooling off and run Fan.

Never attempt to add refrigerant yourself; leaks require licensed service. <br/> Updated: 2026-04-05 <br/> Need help in Castleton, IN? Call (317) 463-1016 or book online.