AC Won’t Turn Off? When to DIY and When to Call a Pro

If your AC won’t turn off, it’s more than just an annoyance; it’s a sign that your air conditioning system is working harder than it should. Typically, your cooling system operates for approximately 15–20 minutes per cooling cycle, two or three times an hour, shutting down once your thermostat detects the desired temperature. When that doesn’t happen, your HVAC system wastes energy, drives up utility bills, and puts unnecessary wear on parts.

The good news? Many causes are easy to identify and fix before they turn into expensive repairs.

Common Reasons Your AC Won’t Turn Off

1. Thermostat Trouble

Your thermostat acts as the command center for your AC unit. If it’s set incorrectly, clogged with dust, or has damaged wiring, it can keep your air conditioning unit running nonstop.

• Incorrect thermostat settings – If the fan setting is set to ON instead of AUTO, the blower fan will run continuously, even when the cooling unit is off.
• Dirty temperature sensors – Dust can throw off readings.
• Loose electrical connections – Disrupt communication between the thermostat and air conditioner.

🏠 DIY Fix: Set the fan to AUTO, clean the thermostat face, and adjust the temperature a few degrees higher than the current room temperature.

2. Stuck Fan Limit Switch

The fan limit switch tells the blower fan when to start and stop. If it’s stuck in override mode, you’ll have a fan blowing constantly, even without a cooling cycle.

🏠 DIY Fix: Switch it back to AUTO. If the faulty fan limit switch won’t reset, it’s time for a replacement.

3. Airflow Restrictions

Poor airflow forces your AC system to overwork itself. Common culprits include:

• Dirty air filter or clogged air filter.
• Blocked or closed room vents.
• Debris around the outdoor condenser unit.
• Leaky ducts reducing air pressure.

🏠 DIY Fix: Replace the air filter, open all vents, and clear vegetation around the outdoor unit.

4. Coil Problems

Your AC has two sets of coils, evaporator coils (inside) and condenser coils (outside). If either set gets dirty, your system efficiency drops.

• Dirty condenser coils – Cannot release heat, resulting in longer run times.
• Frozen evaporator coils – Ice blocks heat absorption, often due to dirty filters, closed vents, or low refrigerant levels.

🏠 DIY Fix: Remove debris from the condenser coil. Leave frozen evaporator coil issues to a pro; thawing them incorrectly can cause damage.

5. Refrigerant Issues

Low refrigerant makes it impossible for the cooling system to circulate cool air effectively. Leaks in coils or refrigerant lines mean your AC unit will continue to run but blow warm air.

👷‍♂️ Pro Fix: A technician can find and repair leaks, then recharge refrigerant to factory specs.

6. Electrical Component Failures

Your air conditioning system relies on electrical components to signal when to stop. Failures include:

• Stuck compressor contactor.
• Damaged circuit board.
• Faulty electrical wiring.

👷‍♂️ Pro Fix: Leave this to an air conditioner repair professional. electrical power issues can be hazardous.

7. Incorrect System Size

• Undersized air conditioner – Runs constantly trying to reach the set temperature.
• Oversized unit – Short-cycles, leading to uneven comfort and poor humidity control.

👷‍♂️ Pro Fix: A load calculation (CSA F280) ensures you have the correctly sized air conditioners for your home.

📖 Read More: CSA F280 HVAC Requirements for Part 9 Buildings

When to DIY vs. When to Call a Pro

🏠 DIY is reasonable for:

• Changing air filters.
• Adjusting thermostat fan settings.
• Clearing debris from the outdoor condenser unit.
• Opening room vents.

👷‍♂️ Call a professional if:

• There’s ice on the evaporator coils.
• You suspect refrigerant leaks.
• Electrical components look burnt or damaged.
• The problem returns after basic fixes.

Preventing an Always-On AC

• Monthly: Check and replace the air filter; clear debris from around the outdoor unit.
• Seasonally: Inspect fan blades, vents, and thermostat settings.
• Annually: Have an HVAC pro clean the condenser coils, lubricate moving parts, and test fan settings.

According to ENERGY STAR, routine maintenance can boost AC efficiency by up to 15% and prevent costly breakdowns.

Key Takeaways

• If your AC runs all day, something’s wrong. Start with thermostat settings and filters.
• Coil, airflow, and refrigerant issues often need professional repair.
• Correct system sizing improves comfort and efficiency.
• Preventive maintenance keeps your cooling and HVAC equipment reliable year-round.

Need Fast Help with an AC That Won’t Turn Off?

Don’t let a constantly running air conditioner drain your wallet and wear out your cooling system. Whether it’s a simple dirty air filter, a stuck fan limit switch, or a deeper issue with your evaporator coils or electrical components, our team at Vernon Air Conditioning, Plumbing & Electrical Services has the tools and expertise to fix it right the first time.

We’ll pinpoint the cause, restore your system’s efficiency, and help prevent future breakdowns with proactive maintenance. Call us today for prompt, professional air conditioner repair because the best time to stop wasted energy and discomfort is right now.