When the AC stops cooling or the furnace blows cold air, the cause is often simple: a thermostat setting, a dirty filter, a tripped breaker or a blocked outdoor unit. The guides below walk through those checks first and explain when the problem needs an HVAC technician.
Common heating and cooling problems
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AC Leaking Water Inside: Drain Line, Drain Pan or Frozen Coil
Water pooling around the indoor AC unit usually means a clogged condensate drain line, a cracked drain pan or a frozen coil. How to check…
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AC Not Blowing Cold Air (Not Cooling): Causes and What to Check First
AC running but not cooling? Start with the thermostat, the air filter and the outdoor unit. How to spot a frozen coil or low refrigerant,…
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AC Not Working at All: Not Turning On or Not Blowing Air
If the air conditioner will not turn on or blow any air, start with the thermostat, the breaker, the outdoor disconnect and the condensate safety…
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Furnace Not Blowing Hot Air (Blowing Cold): Fan Setting, Filter, Flame Sensor or Gas
A furnace that blows cold air is often a thermostat fan set to ON, a clogged filter or an overheating shutdown. Other causes include a…
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Furnace Not Working or Not Turning On: Thermostat, Switch, Breaker and Filter Checks
If the furnace will not start, check the thermostat, the furnace power switch, the breaker and the filter first. When it is an igniter, gas…
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Heat Pump Blowing Cold Air in Heat Mode: Defrost Cycle or a Problem?
Heat pumps blow cooler air than furnaces, and they briefly blow cool air during defrost. How to tell normal from a fault, and what to…
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Thermostat Not Working: Blank Screen, No Power or System Not Responding
A blank or unresponsive thermostat usually comes down to dead batteries, a tripped breaker, a tripped condensate float switch, a blown HVAC fuse or loose…
Before you start
Turn the system off before you change a filter or look inside an access panel. If you smell gas (rotten eggs), leave the house and call your gas company from outside. Refrigerant, gas valves, igniters and control boards are jobs for a licensed technician.