By Project Genie Admin ·
September 3, 2026
Losing air conditioning during a heat wave or heat during a freeze isn't just uncomfortable — for infants, older adults, or anyone with a heart or respiratory condition, it can be genuinely dangerous. Before you call anyone, a few quick checks can tell you whether this is a five-minute fix or a job for a licensed HVAC pro.
Quick answer: Check your thermostat settings, air filter, and breaker first. If the system still isn't working — or you smell gas or burning — stop troubleshooting and get a professional matched fast.
None of the checks below require any tools or HVAC experience — they're the same handful of things a technician would ask about on the phone anyway. Working through them first, in order, either fixes the problem outright or gives whoever you call a much clearer picture of what's actually wrong.
Check the Thermostat Settings
It sounds obvious, but a wrong setting is one of the most common reasons an AC or furnace seems "dead." Make sure it's set to Cool (or Heat) rather than Off or Fan, and that the target temperature is actually a few degrees past the current room temperature — a thermostat set to 72° won't call for cooling if the room is already 70°. If your thermostat runs on batteries, try fresh ones before anything else. A blank or unresponsive display is almost always a battery or power issue rather than a problem with the AC or furnace itself — worth ruling out before you assume the bigger system has failed. If you have a "smart" thermostat, double-check it hasn't been scheduled into a mode (like Away or Eco) that's overriding your manual setting.
Check the Air Filter
A clogged air filter is behind more "my AC isn't working" and "my furnace won't heat" calls than almost anything else. Pull the filter out and hold it up to a light — if you can't see light through it, it's overdue for a swap. A filter that's too dirty can restrict airflow enough to trigger a safety shutoff, which can look like a total system failure when it's really just a $15 fix. This applies to furnaces too, not just AC — restricted airflow is restricted airflow either way, and a filter that hasn't been changed in months is one of the single most common root causes of "no heat" calls in winter as well as "no cooling" calls in summer.
Check the Breaker
HVAC systems trip breakers more than people expect, especially during heavy use in extreme weather. Check your electrical panel for a tripped breaker and reset it once. If it trips again immediately, stop — a breaker that won't stay reset is a sign of a real electrical problem, not something to keep forcing. Repeatedly flipping it back on hoping it holds isn't troubleshooting, it's just delaying a call you're going to need to make anyway, and in the meantime you're putting real strain on the wiring behind that breaker.
Check the Outdoor Unit
For air conditioning, walk outside and check the condenser unit. Make sure it's actually running, and clear away any leaves, grass clippings, or debris that might be blocking airflow around it. A condenser that's caked in debris can't dissipate heat properly, which can shut the whole system down as a protective measure. Give it a couple feet of clearance on all sides if you can — overgrown bushes or stacked yard debris crowding the unit is a surprisingly common, entirely preventable cause of a "dead" AC in the middle of summer. For furnaces, the equivalent check is making sure any exterior venting is clear of snow, leaves, or nesting debris, since a blocked vent can also trigger a safety shutoff.
Frozen Evaporator Coil? Here's What to Do
If you can see ice on the indoor unit or refrigerant lines, don't keep running the system — that usually makes it worse. Turn the system off entirely and give it a few hours to fully thaw before doing anything else. While you wait, swap the air filter if you haven't already, since a restricted filter is a common cause of coil freezing in the first place. If the ice comes back once you turn it back on, it's time to call a pro — a recurring freeze is often a refrigerant or airflow problem that needs a real diagnosis.
When to Stop Troubleshooting and Call a Pro
A few signs mean it's time to stop DIY-checking and get a licensed HVAC technician instead of continuing to troubleshoot:
The breaker trips again after one reset
You hear grinding, screeching, or loud banging from the unit
The system runs constantly but never reaches the set temperature
The coil freezes again after you've thawed and reset it
You smell gas, or notice a burning smell near the furnace
That last one deserves its own note: if you smell gas, don't keep troubleshooting at all. Turn the system off at the breaker if you can do so safely, leave the house, and call your gas utility or 911 from outside — not an HVAC company first.
Get Matched With an Available HVAC Pro Fast
Once you've ruled out the easy fixes, the next problem is usually finding someone who can actually come out today — especially during a heat wave or cold snap, when every HVAC company in town is getting the same calls you are.
Post your emergency HVAC job through Project Genie's Genie 911 category, and licensed pros who are genuinely available bid for it. You get matched with one pro instead of working down a list of busy signals and voicemails. For a broader guide covering other home-systems emergencies too, see our home emergency action guide.
How to Prevent This Next Time
A little regular maintenance goes a long way toward avoiding the mid-heatwave breakdown in the first place:
Replace or clean your air filter on a regular schedule, not just when it looks obviously dirty
Keep the area around your outdoor unit clear of debris and overgrowth
Have your system inspected before peak summer and winter seasons, not during them
Test your carbon monoxide detector along with your smoke detectors — furnace-related CO issues are rare but serious, and a working detector is the cheapest safeguard against them
Frequently Asked Questions
Why is my AC running but not actually cooling the house?
This is usually a dirty filter restricting airflow, low refrigerant, or a frozen coil. Check the filter first — it's the cheapest and most common cause — then check for visible ice on the indoor unit.
Should I keep resetting the breaker if it keeps tripping?
No. A breaker that trips once might be a fluke; one that trips again right after you reset it is telling you there's a real electrical issue. Repeatedly resetting it can be a fire risk — stop and call a licensed pro instead.
How fast can I get an HVAC tech during a heat wave or cold snap?
That depends on who's actually available in your area, which is exactly the problem Genie 911 solves — instead of calling company after company, post your job once and get matched with a pro who's free to take it.
Stay Comfortable, Not Stuck Waiting
Most AC and furnace problems come down to a handful of common causes — start with the thermostat, filter, and breaker before assuming the worst. When it's time for a professional, post your emergency HVAC job free and skip the round of phone calls.