Why did your AC stop working? On a Houston afternoon the question feels urgent, and the answer is often simpler than you fear. A thermostat that switched modes, a filter caked with dust or a breaker that tripped can each make a healthy system look dead. Other causes, like a failed motor part or a refrigerant leak, need a technician. The checks below sort one group from the other without opening any equipment.
Searches for how to fix my air conditioning usually turn up videos of people pulling parts out of the outdoor unit. Please do not. The outdoor cabinet holds high voltage and stored electrical charge, and refrigerant lines run under pressure. This page sticks to checks a homeowner can do safely, then tells you when to stop. If you need help after that, Houston Air & Heating, a free phone line, can connect you with an independent HVAC company nearby, which handles the repair and bills you itself.
Two safety rules before anything else
You smell gas
If you have a gas furnace or water heater and you smell rotten eggs, do not flip switches or try the thermostat. Leave the house, then call your gas utility's emergency line or 911 from outside. CenterPoint Energy delivers natural gas to much of the Houston area.
A carbon monoxide alarm sounds
Get everyone, including pets, out into fresh air and call 911. Carbon monoxide has no smell and no color, and its early symptoms, such as headache, dizziness and nausea, are easy to mistake for the flu.
Safe checks when your AC stops working
Do these in order. Each one takes a few minutes, and each rules out a common cause.
- The thermostat. Confirm it says Cool, not Heat, Off or Fan, and that the set temperature is a few degrees below the room. If the screen is blank or dim, replace the batteries. A schedule or a phone app can also change the setting without you noticing, so check those too.
- The air filter. Pull it out and hold it up to a light. If you cannot see light through it, replace it. A choked filter starves the system of air, which can make it blow weak, warm air or even freeze the indoor coil. The Department of Energy suggests cleaning or changing filters every month or two while the AC is in heavy use.
- The breakers. Most systems have a breaker for the indoor unit and one for the outdoor unit. If one has tripped, switch it fully off, then on again, just once. If it trips again after that, keep it off and phone for help. A breaker that keeps tripping is protecting you from an electrical fault.
- The outdoor unit. With the thermostat calling for cooling, look and listen. Is the fan on top turning? Is the unit humming without the fan moving? Do not reach inside. Clear grass clippings, leaves and stored items away from the sides; the Department of Energy advises keeping dirt, debris and foliage away from the condenser so it can move air freely.
- Water at the indoor unit. Look at the air handler in the attic, closet or garage. Water standing in the pan underneath, or a small switch on the drain line, may mean the float switch has shut the system off on purpose because the drain backed up. Turn the system off and see the AC leaking water guide.
- Ice. Check the copper line at the outdoor unit and, if you can see it safely, the indoor coil. Frost or ice means the coil got too cold. Set the thermostat to Off and the fan to On so warm house air can melt it. Never chip at the ice. Once it thaws, put in a fresh filter, and call a technician if it freezes again.
Make a note of what you find
Whatever the result, jot it down: what the thermostat said, whether the outdoor fan turned, whether a breaker had tripped, whether there was water or ice. Note whether cooling quit all at once or faded over days. Those few facts help a technician narrow the cause before the van door opens, and they make your call shorter.
What the symptoms usually point to
This table matches what you can see with the most common causes. It is a guide for the conversation with a technician, not a diagnosis.
| What you notice | Common causes | What you can safely do |
|---|---|---|
| Nothing runs, thermostat screen blank | Dead batteries, thermostat lost power, tripped breaker, float switch shutoff | Batteries, one breaker reset, look for water at the indoor unit |
| Indoor fan blows, outdoor unit silent | Outdoor breaker or disconnect off, failed capacitor or contactor | Reset the outdoor breaker once, then call |
| Outdoor unit hums, its fan does not spin | Failed capacitor or fan motor | Turn the system off to protect the compressor and call |
| Air from vents is cool but weak | Dirty filter, frozen coil, blocked or leaky ducts, blower trouble | Change the filter, check for ice, open closed vents |
| Ice on the copper line or coil | Low airflow or low refrigerant from a leak | System Off, fan On to thaw, new filter, then call |
| Runs all day, house never reaches the setting | Dirty outdoor coil, refrigerant leak, aging equipment, very hot day | Clear around the outdoor unit, note how far off it is, call |
| Cool but damp and sticky | Short cycling, oversized system, drain trouble, low airflow | Change the filter and ask about sizing and the drain |
HVAC suddenly stopped working, or slowly got worse?
How the problem arrived is one of the best clues you have. Tell the company which one matches.
It quit all at once
A system that worked fine last night and is dead this morning usually lost power or a single part. Think tripped breaker, float switch, thermostat, or an electrical part in the outdoor unit. These tend to be quicker repairs once found.
Thunderstorms, power flickers and outages are worth mentioning on the call, since electrical parts can fail right after one.
It faded over days or weeks
Longer run times, warmer rooms and a higher power bill point to something wearing down: a slow refrigerant leak, a dirty outdoor coil, a clogged filter or a blower losing strength.
Catching this early matters. A system that strains through a Houston August can turn a coil cleaning into a compressor problem.
Why a Houston house can feel clammy while the AC runs
Your air conditioner does two jobs at once. It lowers the temperature, and as warm air passes over the cold indoor coil, moisture condenses out and runs down the drain. On the Gulf Coast, where the air outside is heavy with water much of the year, that second job is a big one.
When the drying part falls behind, the thermostat may read 75 while the house feels sticky. Common reasons include a system that is too large for the house and shuts off before it has pulled much water out, a filter or blower problem that cuts airflow, and a clogged condensate drain. The Department of Energy notes that a blocked drain cuts into the system's ability to control humidity.
Sizing is worth asking about if the clammy feeling has been there since the system went in. Manual J, from the trade group ACCA, is a room by room method for working out how much cooling a house needs. A unit picked by square footage alone can be too big, and an oversized system cycles on and off quickly without drying the air.
What not to do
Leave these alone
- Refrigerant cans or gauges. Federal rules require EPA certification to handle refrigerant in home systems, and low refrigerant means a leak.
- Capacitors and contactors. A capacitor can hold a dangerous charge even with the power off.
- The electrical panel or the outdoor disconnect internals. Resetting a breaker once is fine. Opening covers is not.
- Repeated breaker resets. A second trip is a warning, not a glitch.
- Running the AC while it is iced over. It strains the compressor.
- Hosing down the indoor unit or anything near wiring.
Fine for a homeowner
- Thermostat mode, setting and batteries.
- Swapping the air filter for one of the same size.
- Resetting a tripped breaker once.
- Clearing debris from around the outdoor unit.
- Opening closed supply vents and moving furniture off returns.
- Turning the system off when you see ice or water where it does not belong.
When to stop and call
Call once the safe checks are done and the house still is not cooling, or right away if any of these apply: a breaker trips a second time, you hear grinding, screeching or loud buzzing, you smell burning, the outdoor unit hums with its fan stopped, water is reaching a ceiling or floor, or ice comes back after a thaw and a fresh filter.
Treat it as urgent when the heat itself is the danger. Houston summers are long and humid, and homes without cooling can get hot quickly, and the risk climbs fastest for seniors, infants and people managing a medical condition. If a broken AC is putting someone at risk, the emergency AC repair page explains how the line handles calls at any hour. If it can wait, the AC repair page covers what a normal visit looks like.
What a careful technician checks
A good diagnosis starts with measurements rather than guesses. Expect the technician to read voltage and amperage at the motors, test the capacitor and contactor, look at the indoor coil and the filter, check the condensate drain and float switch, and measure refrigerant pressures and temperatures against the manufacturer's specifications. If the charge is low, the next step should be finding the leak, because the Department of Energy is clear that topping up a leaking system is not a fix.
Before you approve anything, ask for the failed part by name and the price in writing. The AC repair cost guide shows published ranges for common repairs, and if the system is old or the repair is large, the repair or replace guide helps you weigh both options. Whoever does the work, ask for the company's state license number and check it.
Verify the license before work begins. Texas requires anyone contracting to do air conditioning, refrigeration or heating work to hold an Air Conditioning and Refrigeration (ACR) Contractor license from the Texas Department of Licensing and Regulation (TDLR). Ask the company for its ACR license number, then confirm it on the TDLR license search (opens in a new tab). The line does not check this for you.
- Dial the numberAn automated assistant picks up (832) 662-4107 at any hour and asks what you need help with.
- Say what is wrongTell it whether the trouble is cooling or heating, where in the Houston area you are, and what the system is doing.
- Reach a local companyYour call is transferred to an independent, locally owned HVAC company, which gets a short summary of your problem before it answers.
- Work it out with themThat company inspects, quotes, repairs and bills you directly. If nobody can pick up, your name, number and problem are passed on for a call back.
About this line: Houston Air & Heating is a free phone line, not an HVAC contractor. It answers your call and connects you with an independent local heating and air conditioning company, which inspects, quotes and does the work, and which you pay directly. Companies may pay a referral fee. You never pay the line. Read how the line works.