# The AC or heat stopped working: what to check and when to call > Check the thermostat mode, temperature and batteries, then the breaker, furnace switch and filter; a clogged filter can freeze AC. If you smell gas or a carbon monoxide alarm sounds, get out and call from outside. Never heat with a generator, grill or gas oven. Call a licensed HVAC tech for a written quote, and if you rent, tell your landlord in writing. - URL: https://explained.page/ac-or-heat-not-working - Language: en - Last checked: 2026-10-29 - Watch the 1-minute animated guide: https://explained.page/watch?start=ac-or-heat-not-working ## Step by step 1. **The AC or heat stopped working?** Try a few safe checks before you call, and know when to stop and get out. 2. **Check the thermostat first.** Make sure it’s on the right mode and temperature, and try new batteries. It’s the most common simple fix. 3. **Check power and the filter.** Look for a tripped breaker, make sure the furnace switch is on, and replace a dirty filter. A clogged filter can make AC freeze up. 4. **Smell gas or hear the CO alarm? Get out.** Leave right away, then call 911 or the gas company from outside. Don’t flip switches or try to fix it. 5. **Stay warm or cool, safely.** Never use a generator, grill or gas oven to heat a home. Keep space heaters away from anything that burns. In heat, find a cooling center. 6. **Call a licensed HVAC tech.** Ask for the price of the visit up front and a written quote before repairs. For big repairs or a replacement, get a second opinion. 7. **Renting? Tell your landlord in writing.** Many places require landlords to provide working heat, and some require cooling. Report it right away and keep a copy. 8. **Look it up the right way.** Search with your town or state in the words. Pick the official site: it usually ends in .gov. Skip ads and sites that charge for free forms. ## Checklist - Check the thermostat and batteries - Check the breaker, switch and filter - Gas smell or CO alarm: get out - Never heat with a generator, grill or oven - Call a licensed tech; get a written quote - Renting? Tell your landlord in writing ## Quick, safe checks - **Thermostat:** right mode (Cool or Heat), right temperature, new batteries. - **Power:** check for a tripped breaker, and that the furnace switch (often like a light switch near the unit) is on. The outdoor AC unit may have its own shut-off. - **Filter:** replace it if it’s dirty. A clogged filter can make AC freeze up or a furnace shut down. - If AC is frozen, turn it off and run the fan to thaw it. ## When to stop If you smell gas or a carbon monoxide alarm sounds, leave right away and call 911 or the gas company from outside. Don’t flip switches. ## Stay safe meanwhile Never heat your home with a generator, grill or gas oven. Keep space heaters 3 feet from anything that can burn. In extreme heat, drink water, check on older neighbors, and use a cooling center if needed. ## Hiring a tech Ask the visit fee up front and get a written quote before repairs. For big repairs or a replacement, get a second opinion. ## Renting Many places require landlords to provide working heat, and some require cooling. Report it in writing and keep a copy. ## Common questions ### Why is my AC running but not cooling? Common causes are a dirty filter, a frozen coil, a dirty outdoor unit, or low refrigerant. Check the filter and thermostat; the rest needs a tech. Source page: https://explained.page/ac-or-heat-not-working/questions/why-is-my-ac-running-but-not-cooling ### How long should a furnace or AC last? Many last around 15 years or more with maintenance, but it varies. Yearly checkups help catch problems early. Source page: https://explained.page/ac-or-heat-not-working/questions/how-long-should-a-furnace-or-ac-last ### Why is my AC blowing warm air? Check the thermostat is on Cool, the filter is clean, the breaker hasn’t tripped and the outdoor unit is running. If those are fine, it may be low refrigerant or a failed part; call a tech. Source page: https://explained.page/ac-or-heat-not-working/questions/why-is-my-ac-blowing-warm-air ### Why is my furnace blowing cold air? It may be the fan setting (set it to Auto), a dirty filter, or an ignition problem. If it keeps happening, call a tech. Source page: https://explained.page/ac-or-heat-not-working/questions/why-is-my-furnace-blowing-cold-air ### How often should I change my HVAC filter? Often every 1 to 3 months, more with pets or allergies. Check it monthly. Source page: https://explained.page/ac-or-heat-not-working/questions/how-often-should-i-change-my-hvac-filter ### What are signs of carbon monoxide poisoning? Headache, dizziness, nausea, weakness and confusion, often in several people at once. Get out and call 911. Install CO alarms near bedrooms. Source page: https://explained.page/ac-or-heat-not-working/questions/what-are-signs-of-carbon-monoxide-poisoning ### Does my landlord have to fix the heat? In many places, yes: working heat is often required for a home to be livable. Report it in writing; some areas also require cooling. Source page: https://explained.page/ac-or-heat-not-working/questions/does-my-landlord-have-to-fix-the-heat ### Repair or replace an old AC or furnace? If it’s old, needs a costly repair, and keeps breaking, replacing may make sense. Get a second written quote before deciding. Source page: https://explained.page/ac-or-heat-not-working/questions/repair-or-replace-an-old-ac-or-furnace ## Official sources - [Energy Saver (U.S. Dept. of Energy)](https://www.energy.gov/energysaver) - [CDC: carbon monoxide safety](https://www.cdc.gov/) - [Ready.gov: extreme heat and winter weather](https://www.ready.gov/) To find your local office, search for: - "[your city] cooling center" - "[your state] landlord heat requirements" --- General information, not legal or professional advice. Rules differ by state. From explained.page (www.explained.page). Life’s stuff, explained simply.