AC troubleshooting guide · Las Vegas
AC not turning on? Thermostat, breaker and compressor checks for Las Vegas homes
Short answer: if your AC is not turning on, it usually has one of four problems: the thermostat is off, set to the wrong mode or has dead batteries; a breaker has tripped; a safety switch shut the system off because the condensate drain is blocked; or an electrical part has failed. The first three you can check safely in a few minutes. If the indoor fan runs but the outdoor compressor does not, the cause is almost always one for a licensed contractor.
"Not turning on" can mean the whole system is dead, or that only part of it is working. Knowing which part is silent tells you what to check, what to leave alone and what to tell the contractor when you call.
1. Which part is not turning on?
- Nothing happens at all: no air from the vents and no sound from the outdoor unit. Start with the thermostat and the breakers.
- The indoor fan runs but the outdoor unit is silent: the thermostat is calling for cooling, but the compressor and outdoor fan are not starting. See section 4.
- The outdoor unit hums but the fan does not spin: turn the system off at the thermostat instead of letting it keep trying to start, and call a contractor.
- It starts, then shuts off after a short time, over and over: this is called short cycling. The Department of Energy notes that compressor and fan controls can wear out when a system turns on and off too frequently, and recommends having a professional check the electrical connections (energy.gov).
2. Thermostat not working? Check this first
The thermostat is the switch that tells the whole system to run, so a thermostat problem looks exactly like an AC that won't turn on. For a unit that isn't turning on, the Department of Energy advises making sure the thermostat is working: it might need new batteries or might need to be replaced entirely.
- Blank or dim screen: if it uses batteries, replace them.
- Mode and setting: set it to Cool, with the set temperature a few degrees below the current room temperature. If it is set to Off, Heat or Fan, the AC will not cool.
- Schedule or app: programmable and smart thermostats can be holding a schedule or a vacation setting. Check that no "hold" or "away" mode is overriding your setting.
- Correct temperature reading: if the thermostat shows a temperature that is clearly wrong for the room, it will not call for cooling when it should.
- New thermostat? If the AC stopped working right after a thermostat was replaced, the wiring or the settings of the new thermostat may be the problem. A contractor can check it.
If the screen stays blank with fresh batteries, or the system does not respond to any setting, do not take the thermostat apart. Thermostat wiring connects to the control board of the system.
3. Other safe checks
- Breakers: central systems usually have one breaker for the indoor unit and one for the outdoor unit. If one is tripped, reset it once. If it trips again, leave it off and call a professional.
- Drain pan and drain line: many systems have a water-level safety device that shuts off the equipment when the condensate drain is blocked. The Department of Energy's inspection checklist describes this device under the residential code (IRC M1411.3.1). If you can see the pan under the indoor unit and it holds standing water, that may be why the system stopped. Read our AC leaking water guide for what to do next.
- Outdoor unit: make sure nothing is blocking it or covering it. Do not open its panels.
- Air filter: a clogged filter does not usually keep the system from starting, but it can lead to a frozen coil and other problems. If it is dirty, replace it.
4. AC compressor not turning on
The compressor lives in the outdoor unit. It is the pump that moves refrigerant between the indoor and outdoor coils. When the indoor fan runs but the outdoor unit stays silent or only hums, the compressor is not starting. Common reasons include:
- A tripped breaker for the outdoor unit (check it once).
- Worn compressor and fan controls, which the Department of Energy lists as a common electrical control failure.
- A failed start component such as a capacitor or contactor. Our AC repair guide explains what these parts do.
- A compressor problem, one of the more serious repairs. On an older system, ask the contractor to compare repair and replacement in writing.
What not to do: do not open the outdoor unit, touch the capacitor or wiring, or try to "jump start" the compressor. Electrical parts inside the unit are dangerous. Do not add refrigerant either: under Section 608 of the Clean Air Act, adding or removing refrigerant requires EPA certification (EPA). Turn the system off at the thermostat and call a licensed contractor.
5. Las Vegas: why timing matters
An AC that won't turn on is more than an inconvenience in the Las Vegas summer. The National Weather Service in Las Vegas lists a normal July high of 104.5°F and a normal July low of 82.0°F, and the city's all-time record high of 120°F was set on July 7, 2024. A house without cooling heats up quickly in those conditions.
In July and August, the NWS climate summary notes that monsoon moisture brings higher humidity and scattered thunderstorms to the valley, sometimes with damaging gusty winds. If your AC stopped during or after a storm, mention it to the contractor.
If someone at home is older, very young or has a health condition, read our emergency AC guide for heat safety tips and cooling stations while you wait.
6. When to call a licensed AC contractor
- The thermostat has fresh batteries and the right settings, and the system still does not respond.
- A breaker trips again after one reset.
- The indoor fan runs but the outdoor unit does not start, or it hums without the fan spinning.
- The system short cycles: it starts and stops again after a short time.
- You smell burning or hear buzzing or clicking from the outdoor unit. Turn the system off first.
- There is standing water in the drain pan and the system has shut down.
In Nevada, hiring someone to repair 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). Verify the license in the free Nevada State Contractors Board license search before anyone works on your system.
What to tell the contractor: which part is silent (indoor, outdoor or both), what the thermostat shows, whether a breaker tripped, whether you saw water in the drain pan, and when it stopped working.
ClimaVegas does not perform air conditioning work. We connect you with independent air conditioning contractors in the Las Vegas area.
Call to be connected with a local AC contractor
7. More guides for Las Vegas homeowners
- AC not cooling or blowing warm air: a homeowner's checklist.
- AC leaking water: clogged drain lines and what to do first.
- AC freezing up: why ice forms and how to thaw it safely.
- 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 won't my AC turn on?
The most common reasons are a thermostat that is off, set to the wrong mode or has dead batteries, a tripped breaker, a safety switch that shut the system off because the condensate drain is blocked, or a failed electrical part. Check the thermostat and breakers first, and call a licensed AC contractor if that does not solve it.
What should I do if my thermostat is not working?
If the screen is blank or dim and it uses batteries, replace them. Make sure it is set to Cool, below room temperature, and reading the correct temperature. If the screen stays blank or the system still does not respond, the thermostat or its wiring may need to be checked or replaced by a professional.
Why is my AC compressor not turning on when the indoor fan runs?
If air moves but the outdoor unit stays silent or only hums, the compressor is not starting. Check the outdoor unit's breaker once. Otherwise the cause is usually electrical, such as worn compressor and fan controls, a failed start component or a compressor problem. Turn the system off and call a licensed contractor; do not open the outdoor unit.
Can a clogged drain stop my AC from turning on?
Yes. Building codes allow a water-level safety device that shuts off the equipment when the primary condensate drain is blocked, so the system stops before the pan overflows. If you see standing water in the drain pan, read our AC leaking water guide.
How many times should I reset the AC breaker?
Once. If the breaker trips again, leave it off and call a licensed AC contractor. Repeated tripping points to an electrical problem.