AC troubleshooting guide · Las Vegas
AC making noise or smells like burning? What each sign can mean
Short answer: an AC making noise is not always a problem: a low hum, a click when it starts or stops and the whoosh of moving air are normal. Grinding, screeching, banging, loud buzzing or hissing are warning signs that a part is loose, worn or failing. If the AC smells like burning, turn it off at the thermostat and at the breaker and call a licensed AC contractor. If you see smoke or flames, get everyone out and call 911.
Your air conditioner has fans, motors, a compressor and electrical parts, and each one makes a characteristic sound when something goes wrong. Knowing which sounds are normal and which are not helps you decide whether to keep the system running and helps you describe the problem clearly when you call a contractor.
1. If your AC smells like burning, do this first
- Set the thermostat to Off.
- Turn off the AC breakers at the electrical panel (indoor unit and outdoor unit).
- If you see smoke or flames, or the smell keeps getting stronger, get everyone out of the house and call 911.
- Do not turn the system back on until a licensed AC contractor has looked at it.
A smell like hot plastic, melting wires or something electrical burning can come from an overheating motor or a failing electrical part. It is not something to watch and wait on.
Rotten-egg smell? That can be a natural gas leak from a gas furnace or other gas appliance. Leave the area immediately and, from a safe place, call 911 and Southwest Gas at 877-860-6020 (Southwest Gas). Do not switch lights, thermostats or appliances on or off.
Musty smell? That points to moisture, such as a clogged drain or standing water near the indoor unit. The EPA explains that the key to mold control is moisture control (EPA). See our AC leaking water guide.
2. Sounds that are usually normal
- A low, steady hum from the outdoor unit while it runs.
- A single click when the system starts or stops.
- The whoosh of air at the vents and a soft sound from the indoor fan.
- A brief gurgle or drip from the indoor unit as condensation drains.
3. AC noises that are warning signs
- Grinding or screeching: often a fan or blower motor with worn bearings. Turn the system off; running it can turn a motor problem into a bigger one.
- Banging, clanking or thumping: something is loose or broken, such as a fan blade, a motor mount or a part inside the compressor. Turn the system off.
- Loud buzzing or humming while the outdoor fan does not spin: often an electrical problem, such as a failing start component or a motor that cannot start. Turn the system off and do not touch the parts inside the unit.
- Repeated clicking that does not stop: can point to an electrical control or a thermostat problem.
- Hissing or bubbling: can mean a refrigerant leak or a leaking duct. Refrigerant work requires an EPA-certified technician under Section 608 of the Clean Air Act (EPA).
- Rattling: a loose panel, screws or debris inside or around the outdoor unit. With the power off at the breaker, you can clear sticks and leaves from around the unit, but do not open it.
- Squealing at startup: on older systems with belt-driven blowers, a worn belt; on newer systems, a motor issue.
4. What not to do
- Do not keep running a system that grinds, bangs or smells like burning.
- Do not open the outdoor unit, the electrical panel or touch the capacitor. Electrical parts can hold a dangerous charge even after the power is off.
- Do not spray oils, cleaners or chemicals into the unit or onto motors and coils.
- Do not reset a tripped breaker more than once. See our AC tripping breaker guide.
5. Why a tune-up catches many of these early
ENERGY STAR's maintenance checklist for a professional visit includes tightening electrical connections and measuring voltage and current on motors, lubricating moving parts, and checking that the system starts, operates and shuts off properly. It notes that faulty electrical connections can cause unsafe operation and reduce the life of major components, and that parts lacking lubrication cause friction in motors (ENERGY STAR).
In Las Vegas, the National Weather Service describes blowing dust and sand during strong winds, and summer normals above 100°F mean many systems run for long stretches from late spring into fall (NWS). Long run times and dust are hard on motors and fans, which is one reason an annual check before the hot season matters here.
6. When to call a licensed AC contractor
- Any burning or electrical smell, even if it goes away.
- Grinding, screeching, banging or loud buzzing.
- Hissing near the refrigerant lines or the indoor coil.
- A new noise together with weak or warm air (see our AC not cooling guide).
In Nevada, hiring someone to work on the air conditioning in your home requires a licensed contractor, and the exemption for jobs under $1,000 does not apply to air conditioning work (NRS 624.031). Before anyone works on your system, verify the license in the free Nevada State Contractors Board license search, and ask whoever handles refrigerant for their EPA 608 certification.
What to tell the contractor: what the sound or smell is like, whether it comes from the indoor or outdoor unit, when it happens (at startup, all the time, at shutdown), whether you turned the system off, and the age of the system if you know it. A short phone video of the sound can help.
ClimaVegas does not perform air conditioning work. We connect you with independent air conditioning contractors in the Las Vegas area.
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7. More guides for Las Vegas homeowners
- AC not cooling or blowing warm air: a checklist of the safe first checks.
- AC not turning on: thermostat, breakers and a compressor that won't start.
- AC leaking water: clogged drain lines and what to do first.
- AC freezing up: why ice forms and how to thaw it safely.
- AC tripping the breaker: reset once, then what repeated trips and short cycling mean.
- AC repair cost: typical prices for common repairs, from published 2026 data.
- AC replacement cost: new unit prices, lifespan and 2026 incentives.
- Heat pump vs AC in Las Vegas: how they compare in a desert climate.
- Emergency AC guide: first checks and heat safety.
- AC repair in Las Vegas: the common repairs, explained.
- AC repair in Henderson: city permits and HOA rules.
- HVAC guide for Las Vegas: efficiency rules, maintenance and permits.
- Heating repair guide: furnaces, heat pumps and carbon monoxide safety.
Frequently asked questions
Why is my AC making a loud noise?
Grinding or screeching often comes from a fan or blower motor with worn bearings, banging or clanking from a loose or broken part, loud buzzing from an electrical problem, and hissing from a refrigerant or duct leak. A low hum, a click at startup and the sound of moving air are normal. For warning sounds, turn the system off and call a licensed AC contractor.
What should I do if my AC smells like burning?
Turn the AC off at the thermostat and at the breakers, and do not turn it back on until a licensed AC contractor has checked it. If you see smoke or flames, or the smell keeps getting stronger, get everyone out of the house and call 911.
Is it normal for my AC to hum?
A low, steady hum from the outdoor unit while it runs is normal. A loud buzz or hum while the outdoor fan does not spin is not; it often points to an electrical problem. Turn the system off and call a professional.
Why is my AC hissing?
Hissing or bubbling can mean a refrigerant leak or a leaking duct. Refrigerant can only be handled by an EPA-certified technician under Section 608 of the Clean Air Act, so this is work for a professional.
Should I turn off my AC if it is making a grinding noise?
Yes. Grinding usually means metal parts are rubbing, often in a motor. Running the system can make the damage worse. Turn it off at the thermostat and call a licensed AC contractor.
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