Why Your AC Won’t Start, Stop, or Shut Off (and What You Can Actually Do About It)

May 9, 2025 | Semper Fi | Air Conditioner Troubleshooting, Air Conditioner Tune-Up, Air Conditioning, Air Conditioning Repair, Air Conditioning Replacement, HVAC, Maintenance

Why Your AC Won’t Start, Stop, or Shut Off (and What You Can Actually Do About It)

Let’s be honest—AC issues always seem to hit at the worst possible time. Whether it won’t turn on, won’t stop running, or is working non-stop without cooling, it’s a headache you don’t have time for. But don’t sweat it (literally)—we’ve got the rundown of what might be wrong and how you can fix it yourself before calling in the pros.

So, Your AC Won’t Start?

If your AC isn’t starting, consider the following potential causes:

Thermostat Settings: Make sure it’s set to “cool”, and your desired temperature is set below the current room temperature. It’s simple but often overlooked.
Power Issues: Flip your breaker panel and check for anything tripped. A quick reset might do the trick. It could be as simple as that!
Clogged Air Filter: A dirty filter can constrict the airflow and trigger safety shutoffs. Try swapping it out and see if that solves the problem.
Emergency Shut-Off Switches: Look around the indoor and outdoor units—sometimes there’s a manual switch that’s been flipped off without you realizing it.
Blocked Drain Line: If the pan is full or the line is clogged, it might shut down for safety. Clear it out and you’re good to go.
Faulty capacitors or contactors: These store energy to start-up your system. If they’re failing, your AC may not start. You’ll need diagnosis and replacement from a pro.
Professional assessment: If you’re hearing weird sounds or nothing’s happening at all, the compressor could be dead. Time to get someone out to take a look.

Your AC Won’t Turn Off

If your system is running a marathon and refuses to quit, here’s what might be happening:

Thermostat Malfunction: If it’s misreading the temp or is outdated, it might not know when to shut off. Check to see if it’s functioning correctly.
Dirty Outdoor Coils: The coils help release heat. When they become gunky, your AC has to work overtime. Regularly clean them to help your system chill out.
Low Refrigerant: When there’s a leak, your AC can’t reach the set temp and just keeps running. If you suspect a leak, call in a professional tech.
Fan Limit Switch Issues: This switch controls your blower fan. If it’s stuck in the “on” position, the fan won’t stop. Get it checked by a professional.

It’s Running… But Your House Is Still Hot

This might be the most frustrating problem: your AC is running constantly, but you’re still sweating. Here’s what could be going on:

Wrong- Sized Unit: Too small and it never catches up. Too big and it cycles on and off too fast. You might need a new unit installation.
Leaky Ducts: Cooled air might be escaping through holes in the ductwork. If so, get them checked and have them sealed
Closed Vents or Blockages: Walk around and make sure none of your vents are closed or blocked.
Older System: If it’s more than 10–15 years old, it might just be worn out. You may want to consider a replacement.

Keep It Running Smoothly With These Quick Maintenance Tips

Change Filters: Every 1–3 months. Seriously, it makes a big difference.
Tune-Ups: Book a pro to tune up your system once or twice a year.
Clean the Outdoor Unit: Keep leaves, dirt, and debris away as much as possible. Gently hose off the condenser coils too.
Use Your Thermostat Wisely: A smart thermostat can optimize cooling schedules and save you money over time.

Still No Luck?

Sometimes, the best (or easiest) move is to bring in an expert. Don’t hesitate to diagnose and resolve lingering issues with a certified HVAC technician. We are here to help!

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