When your AC isn’t cooling (or your heat won’t turn on), it’s tempting to assume the worst. A lot of the time, it’s something simple — and you can catch it quickly.
Safety note: If you smell gas, see smoke, or hear loud electrical buzzing, turn the system off and call a professional.
1) Check the thermostat (mode + setpoint)
- Make sure it’s set to Cool (for AC) or Heat (for furnace/heat pump).
- Lower (or raise) the setpoint by 3–5° and wait a few minutes.
- Replace batteries if needed.
2) Confirm the system has power
- Check your breaker panel for a tripped breaker.
- For some systems, there’s a nearby service switch (looks like a light switch) that can get turned off.
3) Replace the air filter
A clogged filter can:
- reduce airflow
- cause AC coils to freeze
- make heat run poorly
If it looks dirty, replace it.
4) Make sure vents aren’t blocked
- Open supply vents.
- Don’t block returns with furniture or rugs.
5) If the AC is running but not cooling: check the outdoor unit
- Clear leaves/debris and keep 2–3 feet of clearance.
- Listen for the outdoor fan.
- If the outdoor fan isn’t running, turn the system off and call.
6) If the furnace/heat won’t start: check the door panel
Many furnaces won’t run unless the front panel is seated correctly. If it’s slightly open, the safety switch prevents startup.
7) Look for ice on refrigerant lines (AC/heat pump)
If you see ice/frost:
- Turn Cooling off
- Set the fan to On to thaw
- Replace the filter
If it refreezes, it needs service.
8) Check the condensate drain (AC / high‑efficiency furnaces)
A clogged drain can trip a safety switch and shut the system down. If you see water around the unit, it may be a drain/pan issue.
9) When to call a pro
Call if:
- breaker trips repeatedly
- burning smell / electrical buzzing
- ice keeps returning
- outdoor unit won’t run
- system runs but temperature doesn’t change
Want Fixurion to take a look?
Send us what you’re seeing (symptoms, thermostat model, and address/city) and we’ll recommend next steps.