Common HVAC Problems & Fixes

Your HVAC system works hard year-round, so it’s no surprise it may act up from time to time. Before you call for service, check out these common problems and easy fixes that could save you time and money.

1. System Won’t Turn On

Before assuming the worst, check these basics:

Ensure the thermostat is set to “Heat” or “Cool” and not “Off.”
Replace thermostat batteries if applicable.
Check the breaker box for tripped circuits.
Inspect the furnace or air handler switch — it’s often mistaken for a light switch!

2. Weak or No Airflow

Poor airflow can cause uneven temperatures and system strain. Common causes include:

Dirty filters (replace every 60–90 days).
Blocked or closed vents.
Leaky or crushed ductwork.
Failing blower motor or capacitor.

3. System Runs Constantly

If your system never cycles off, it could be due to:

Incorrect thermostat setting or calibration.
Clogged filters restricting airflow.
Leaky ductwork losing conditioned air.
Low refrigerant levels or dirty coils.

4. Uneven Heating or Cooling

When some rooms are too hot and others too cold, check for:

Blocked or undersized ducts.
Dirty filters or coils.
Poor insulation or window leaks.
Closed dampers or vents.

5. Strange Noises

Banging or clanking: Loose parts or debris in the blower or fan.
Whistling: Air leaks or high static pressure in ducts.
Clicking: Electrical issue with the capacitor or relay.
Buzzing: Failing compressor or loose wiring (call a pro).

6. AC Not Cooling

If your AC is blowing warm air:

Make sure the outdoor unit is clear of debris and running.
Clean or replace the air filter.
Check the thermostat fan mode (set to “Auto,” not “On”).
Low refrigerant or dirty coils may require professional service.

7. Furnace Not Heating

Check the pilot light or ignition system.
Make sure the gas valve is open.
Inspect filters for clogs.
Reset any triggered limit switches or safety features.

8. Water Around the Unit

Condensation is normal, but puddles indicate a problem:

Clogged condensate drain line.
Frozen evaporator coil.
Improperly insulated drain lines.

9. High Energy Bills

If your bills spike suddenly:

Dirty filters or coils forcing longer runtimes.
Leaky ducts wasting conditioned air.
Thermostat miscalibration or old equipment inefficiency.

When to Call a Professional

DIY fixes cover many issues, but call an HVAC pro if:

You suspect refrigerant leaks or electrical problems.
Your system short cycles or freezes up frequently.
You hear loud metallic noises or smell burning odors.

FAQ

How do I reset my HVAC system?

Turn off the thermostat, switch the breaker off for 30 seconds, then restore power. This can clear minor control board faults or lockouts.

Why does my AC freeze up?

Restricted airflow or low refrigerant can cause the evaporator coil to freeze. Turn the system off, let it thaw, and replace your filter. If it freezes again, call a technician.

Shop the basics:
Filters · Maintenance Tools · Thermostats