In McAllen, an AC that won’t start is an urgent problem, not a “I’ll deal with it this weekend” situation. Before you call for service, there are a few things worth checking yourself. Some are simple fixes but others confirm that you need to call a technician.
Here’s a systematic way to work through it.
Step 1: Check the Thermostat
It sounds obvious, but thermostat settings are the first thing to rule out.
- Make sure it’s set to “cool,” not “fan only” or “heat”
- Confirm the set temperature is lower than the current room temperature
- If the thermostat display is blank or dim, replace the batteries, many thermostats run on AA batteries and will lose function when they die
- If you have a smart thermostat, check whether it lost its WiFi connection or went into an unexpected mode
If the thermostat looks fine and the system still won’t respond, move on.
Step 2: Check the Circuit Breaker
AC systems are on their own dedicated breakers, it’s usually two of them, one for the indoor air handler and one for the outdoor condenser. Go to your electrical panel and look for any breakers in the “off” position or sitting halfway between on and off (tripped).
Reset a tripped breaker by flipping it fully off and then back on. If the system starts and the breaker holds, you may have had a temporary power surge. If the breaker trips again within a few minutes of restarting the AC, stop resetting it, you probably have an electrical issue that needs a professional.
Step 3: Check the Disconnect Box
There’s usually a metal disconnect box mounted near the outdoor condenser unit. Inside is a pull-out block that can be removed to cut power to the outdoor unit. Sometimes these get accidentally disconnected, could have been by a homeowner doing yard work, by children, or occasionally by a pest getting inside the box. Check that the disconnect block is fully seated.
Step 4: Check the Indoor Air Handler
The indoor unit has its own power switch, it looks like a regular light switch and is usually mounted on the wall near the air handler. If someone flipped it off thinking it was a regular switch (it happens), the system won’t run.
Also check the float switch, this is a small safety device in the drain pan that shuts the system off if the condensate drain line backs up. If the float switch has tripped, you’ll need to clear the drain line before the system will restart. Clogged drain lines are common in humid climates and something a tune-up would catch before it causes a shutdown.
Step 5: Give It a Few Minutes
If the system ran and then shut off unexpectedly, the compressor has a time-delay feature that prevents it from restarting immediately. This protects the compressor from pressure damage. Wait 5 minutes after a shutdown before trying to restart.
When to Call a Technician
If you’ve checked all of the above and the system still won’t start, you’re likely looking at one of these issues.
Failed capacitor
Capacitors give the compressor and fan motors the initial electrical kick to start. When a capacitor fails, the motor hums but won’t start, or the system attempts to start and immediately shuts off. Capacitor failure is one of the most common AC repairs in South Texas, the heat accelerates their degradation. It’s typically a $150–$300 repair.
Failed contactor
The contactor is a relay switch in the outdoor unit that sends power to the compressor. When it fails, the outdoor unit won’t engage even if everything else is working. You may hear the indoor unit running but the outdoor unit is silent. Relatively inexpensive to replace, but requires a licensed tech.
Low refrigerant / low-pressure lockout
Systems with low refrigerant will sometimes shut down on a low-pressure safety switch and refuse to restart until the issue is addressed. If this is the cause, a refrigerant pressure check will confirm it, and the underlying leak needs to be found and repaired.
Failed compressor
A compressor that has failed entirely won’t start, and there’s typically a humming or clicking sound from the outdoor unit as the system tries to engage. This is the most expensive AC repair, often $1,500–$2,500 or more, and on older systems it often makes more sense to replace the whole unit. You can read about signs your system may be beyond repair if you’re trying to make that call.
In South Texas, Don’t Wait on This
A failed AC in McAllen in the summer isn’t a comfort inconvenience, it could become a health situation quickly, especially for children, elderly family members, or anyone with respiratory conditions. Read about when to call for emergency AC repair in McAllen if you’re unsure whether your situation warrants a same-day call.
If the system is running but blowing warm air rather than not starting at all, that’s a different problem, read about why your AC is blowing warm air for that diagnosis.
Frequently Asked Questions
Why does my AC hum but not turn on?
A humming sound from the outdoor unit usually points to a failed capacitor, the compressor is trying to start but can’t get the electrical boost it needs. This is one of the more common and affordable AC repairs: typically $150–$300 for a capacitor replacement.
My AC worked yesterday, why won’t it turn on today?
Sudden failures are often electrical: a tripped breaker, a failed capacitor, or a tripped float switch from a clogged drain line. Run through the checklist above before calling for service, several of these have simple fixes.
How long can I go without AC in McAllen in summer?
Not long, especially with children or elderly family members in the home. South Texas heat can push indoor temperatures dangerously high within hours. If your AC fails and you can’t get same-day service, a portable AC unit for a bedroom or two can make a significant difference while you wait.
Is it worth repairing an old AC that won’t turn on?
It depends on the repair and the system’s age. A capacitor replacement on a 7-year-old system is an easy yes. A compressor replacement on a 14-year-old system is usually a no, at that point, replacement often makes more financial sense.
Need Help Now?
Mission Air Conditioning’s AC repair services cover everything from capacitor failures to compressor diagnostics across McAllen and the Rio Grande Valley. If your system won’t start and you’ve worked through the steps above, give us a call, we’ll diagnose the problem and give you a price before any work starts. Reach us at missionaircon.com.