AC troubleshooting guide · Las Vegas
AC not cooling or blowing warm air? A Las Vegas homeowner's checklist
Short answer: if your AC is not cooling or is blowing warm air while it runs, the usual causes are a thermostat that is set wrong or has weak batteries, a clogged air filter, a dirty or blocked outdoor unit, or low refrigerant from a leak. If the air from the vents is warm, the outdoor unit is often not running at all, for example because a breaker tripped or an electrical part failed. The first four checks below are safe for any homeowner; refrigerant and electrical repairs are not.
"AC not cooling" covers a few different situations: the system runs all day and the house never reaches the set temperature, the vents blow air that feels warm, or the system cools in the morning and falls behind in the afternoon. This checklist helps you tell them apart, fix the simple causes yourself, and describe the problem clearly when you call a contractor.
1. First, figure out which problem you have
- Air is cool but weak, and the house never catches up: often an airflow problem (dirty filter, closed or blocked vents, dirty coils) or a system working at its limit in extreme heat.
- Air from the vents is warm or room temperature: the indoor fan is running, but the outdoor unit may not be. Go outside and look: is the outdoor fan spinning, and can you hear the unit running?
- Cooling gets worse over days or weeks: a slow refrigerant leak or coils that are getting dirtier are common explanations.
- You see ice on the indoor coil or the copper lines: stop here and read our guide to an AC freezing up. Running a frozen system can damage it.
2. Safe checks you can do yourself
The U.S. Department of Energy lists a wrong thermostat setting, a dirty filter and a clogged drain among the common reasons a unit is not cooling properly (energy.gov). Go through these in order:
- Thermostat: set it to Cool (not Fan, Heat or Off), set the temperature a few degrees below the room temperature, and put the fan on Auto. If the display is blank or dim and it uses batteries, replace them. Check that it is reading the correct room temperature.
- Air filter: pull it out and look at it. If it is gray and packed with dust, replace it. A clogged filter restricts airflow and reduces the system's ability to cool. ENERGY STAR recommends inspecting, cleaning or changing filters once a month (ENERGY STAR).
- Breakers: most central systems have a 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: repeated tripping points to an electrical problem that needs a professional.
- Outdoor unit: remove anything that blocks airflow around it, such as weeds, boxes, covers or piles of leaves. Do not open the unit's panels. The Department of Energy notes that keeping the outdoor unit clean helps prevent overheating.
- Vents and returns: make sure supply registers are open and that furniture, rugs or curtains are not covering them or the return grille.
After these checks, give the system some time to run and feel the air at a vent close to the indoor unit. If it is still warm, the cause is probably something you should not try to fix yourself.
3. What not to do
- Do not add refrigerant. Under Section 608 of the Clean Air Act, technicians who maintain, service, repair or dispose of equipment that could release refrigerant must be EPA-certified, and adding or removing refrigerant is one of the activities that requires certification (EPA).
- Do not open electrical panels or touch the capacitor. Electrical parts inside the units are dangerous to handle; that work belongs to a professional.
- Do not reset a breaker again and again or keep restarting the system if it shuts itself off.
- Do not spray cleaners into the indoor unit or use strong chemicals on the coils. Coil cleaning is part of a professional maintenance visit.
4. Common causes a contractor will look for
- Low refrigerant from a leak. The Department of Energy advises calling a trained technician to repair the leak and recharge the system. Refrigerant is not used up like fuel; the EPA asks homeowners to request that technicians locate and repair leaks instead of "topping off" a leaking system (EPA).
- Dirty coils. ENERGY STAR notes that dirty evaporator and condenser coils reduce the system's ability to cool and make it run longer.
- Airflow and blower problems. According to ENERGY STAR, airflow problems can reduce a system's efficiency by up to 15 percent.
- Worn electrical controls. The compressor and fan controls can wear out, especially when a system turns on and off too often; the Department of Energy recommends having a professional check the electrical connections.
- Leaking or disconnected ducts. The Department of Energy recommends working with a professional to clean and seal leaking or constricted ducts; it estimates that air loss through ducts accounts for about 30 percent of a cooling system's energy consumption.
5. Why Las Vegas is harder on air conditioners
According to the National Weather Service in Las Vegas, the normal high in July is 104.5°F and the normal low is 82.0°F (1991–2020 normals). The all-time record high is 120°F, set on July 7, 2024, and the record warmest low is 95°F, most recently on July 1, 2013. With nights that warm, many systems barely rest during the summer.
The NWS climate summary also describes the blowing dust and sand that come with strong winds in the valley, and an urban heat island that keeps nights near the center of the valley warmer than outlying areas. Dust clogs filters and coats outdoor coils, which is one reason the monthly filter check matters more here than in milder climates.
On the hottest afternoons it can be normal for a healthy system to run almost nonstop and for the house to drift a few degrees above the set point. What is not normal is warm air from the vents, a system that never shuts off on a mild day, or cooling that gets worse each week.
6. When to call a licensed AC contractor
- The air is still warm after you checked the thermostat, filter, breakers and outdoor unit.
- A breaker trips again after one reset.
- The outdoor unit hums but the fan does not spin, or it does not start at all.
- You see ice on the indoor coil or refrigerant lines.
- You hear grinding, screeching or buzzing, or you smell burning. Turn the system off at the thermostat and the breaker first.
- Water is leaking from the indoor unit (see our AC leaking water guide).
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). 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: whether the air is weak or warm, whether the outdoor unit runs, what you already checked, when the problem started, and the age of the system if you know it. It saves time on the visit.
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 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.
- 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 running but not cooling?
The most common causes are a thermostat that is set wrong or has weak batteries, a clogged air filter, a dirty or blocked outdoor unit, and low refrigerant from a leak. Check the thermostat, filter, breakers and outdoor unit first. If the air is still warm, call a licensed AC contractor.
Why is my AC blowing warm air?
If the indoor fan runs but the air is warm, the outdoor unit may not be running, often because a breaker tripped or an electrical part failed. It can also be a thermostat set to Fan or Heat, or a refrigerant leak. Check the thermostat and breakers once; electrical parts and refrigerant are work for a licensed, EPA-certified technician.
Can I add refrigerant to my AC myself?
No. Under Section 608 of the Clean Air Act, anyone who adds or removes refrigerant must be EPA-certified. A low charge usually means a leak. The EPA recommends asking the technician to locate and repair the leak instead of topping it off.
Is it normal for my AC to struggle on the hottest Las Vegas days?
Systems work hardest when it is extremely hot. The National Weather Service normal high for July in Las Vegas is 104.5 degrees and the city reached a record 120 degrees on July 7, 2024. Long run times on those days can be normal, but warm air from the vents is not.
How do I check that an AC contractor is licensed in Nevada?
Search the company name or license number in the free Nevada State Contractors Board license search at nvcontractorsboard.com. In Nevada, air conditioning work is contractor work even for jobs under $1,000.
En español: ¿Tu AC no enfría? · Blog