HVAC troubleshooting
Common HVAC Problems and What They May Mean
Start with the symptom. Each guide gives a quick answer, the likely causes, checks that are safe for a homeowner and the signs that it's time for a professional.
Cooling problems
- AC Not CoolingAn air conditioner that runs without cooling is most often held back by a clogged filter, a thermostat set to the wrong mode, a dirty outdoor coil, or blocked airflow.
- AC Blowing Warm AirWhen vents blow warm air, the indoor blower is usually working but the outdoor condenser has stopped cooling.
- AC Freezing UpAn air conditioner freezes when the indoor coil gets too cold, usually because not enough warm air moves across it or the refrigerant charge is low.
- AC Leaking WaterWater leaking from an indoor AC unit usually comes from a clogged condensate drain line, a cracked or rusted drain pan, a loose drain fitting, or a frozen coil that is melting.
- AC Making NoiseA noisy AC may have loose panels, debris in the outdoor fan, a worn motor bearing, a failing capacitor or contactor, or a strained compressor.
- AC Not Turning OnWhen an air conditioner will not turn on, the first suspects are simple: dead thermostat batteries, the wrong thermostat mode, a tripped breaker, a service switch turned off, or a full condensate pan that triggered a safety shutoff.
Heating problems
- Furnace Not HeatingA furnace that will not heat is often stopped by a thermostat setting, a tripped breaker, a service switch turned off, a clogged filter, or a closed gas valve.
- Furnace Blowing Cold AirA furnace blowing cold air often has the thermostat fan set to ON, so air keeps moving between heating cycles.
- Heat Pump Not HeatingA heat pump that seems not to heat may be in a normal defrost cycle, set to the wrong thermostat mode, or held back by a clogged filter or an iced outdoor coil.
First checks that apply to almost every problem
- Look at the air filter and replace it if it's gray or clogged.
- Confirm the thermostat is set to the right mode and a sensible temperature, and replace its batteries if it uses them.
- Check the breaker panel for a tripped HVAC breaker. Reset it once only.
- Make sure supply registers are open and return grilles aren't blocked by furniture.
- Clear leaves and vegetation from around the outdoor unit.
Call now
Still not sure what's wrong?
Call and describe the symptom. A local HVAC provider can tell you what's likely going on and how urgent it is.
Call NowThe line is for homeowners who need HVAC or AC repair, replacement or installation. It can't help with billing or service already scheduled with a company.
Which HVAC problems should be treated as urgent?
A gas smell, a burning or electrical smell, smoke, or a carbon monoxide alarm. Leave the house for gas or CO and call 911 or the gas utility from outside. Loss of cooling in extreme heat is also urgent for infants, older adults and anyone with health conditions.
What should I check before calling about an HVAC problem?
Look at the air filter, confirm the thermostat mode and setpoint, replace thermostat batteries if it uses them, and check whether a breaker has tripped. Reset a breaker once only. Make sure registers are open and the outdoor unit isn't blocked.
Why do the problem guides tell me not to open the equipment?
Outdoor units and furnaces contain high voltage, capacitors that can hold a charge, gas valves and refrigerant under pressure. Watching, listening and noting what you see is safe and genuinely useful to the provider.
Why does my AC struggle more in Alabama than it did elsewhere?
Long, humid summers mean the system runs for months and has to remove moisture as well as heat. Small problems like a dirty coil or a partly clogged drain show up faster when the system rarely gets a break.
Is ice on my air conditioner ever normal?
Not on a cooling system in summer. Ice usually points to poor airflow or low refrigerant. A heat pump in winter is different: frost that clears during a defrost cycle is normal.
What details help a provider diagnose a problem faster?
When it started, what the system does and doesn't do, any sounds or smells, whether a breaker tripped, and the type and approximate age of the equipment. Photos of the outdoor unit's label can help too.