Learn why your AC is not turning on after winter and find easy checks to ensure it is ready for the summer heat.
After a long winter, you’re ready to enjoy cool air again—but what if your AC won’t turn on? Don’t worry, this is a common issue after months of inactivity. The problem could be as simple as a tripped breaker, a thermostat setting, or a dirty filter. However, cold weather can also take a toll on your system. Before calling a professional, it’s a good idea to do a quick check yourself. This can help you identify possible issues, save time, and even avoid unnecessary repair costs. Let’s go through some common reasons your AC might not be working and what you can do about it.
Why won’t my AC turn on?
Don’t panic; it’s quite common for AC not to start after months of inactivity. The reason for that might be in a simple tripped breaker, or in a thermostat setting, or a clogged filter. However, winter could also harm your system. You have three opinions, if your AC is not turning on. You can call a professional HVAC contractor to perform a maintenance and possible repair, or you can try to solve the problem yourself, or (what is recommended) conduct a quick examination yourself, collect an anamnesis, and call specialists already knowing all the symptoms of the problem.
Reason 1. Tripped breaker and blown fuses
A tripped breaker or blown fuse is often the easiest fix. AC systems pull a lot of power, and after being unused for months, a sudden startup can trip a breaker. But before resetting it, ensure you know why and when it happens. If it happens again immediately, it could mean a short circuit, motor issue, or electrical overload, in other words, things you can’t ignore.
Likewise, a blown fuse in the disconnect box near your outdoor unit could be the reason. But if you replace the fuse and it blows again, it’s time to call in a pro too. Also, if the breaker trips after the air conditioner has been running for some time, it could mean the compressor is struggling (due to low refrigerant, a bad capacitor, or a failing motor). You’d better touch your breaker, and if it feels warm to the touch, it could be overloaded or failing. This is a sign you should call an electrician, not just an HVAC tech.
Reason 2. Faulty thermostat
Your thermostat is the AC boss, and if it’s not working, your system won’t start either. The most common thermostat issues are dead batteries or incorrect settings (it should be set on “cool” and below room temperature). Smart thermostats can also lose Wi-Fi connections or need firmware updates. If adjusting settings and replacing batteries doesn’t help, try bypassing the thermostat by manually connecting the wires at the control board; if the AC kicks on, you’ve found the problem.
Besides dead batteries or incorrect settings, a thermostat can fail because its internal sensor is dirty (and your thermostat simply reads the wrong temperature). Clean it gently with a soft brush or compressed air. Also, if the thermostat wire runs through an attic or crawlspace, rodents or old insulation staples might have damaged it.
Reason 3. Dirty air filters and blocked vents
A heavily clogged air filter can overwork your system, causing it to overheat and shut down for protection. Blocked vents cause the same problem. Some modern ACs have pressure sensors that prevent startup when airflow is too low. So in case of AC not working, the first thing to do is to replace air filters and ensure all vents are open and unobstructed. If your system still won’t start, dirt buildup inside the unit could be causing that.
Reason 4. Low on refrigerant
Your AC doesn’t “use up” refrigerant like fuel; it should stay at the same level unless there’s a leak. If refrigerant is low, your system may fail to turn on because modern units have low-pressure safety switches to prevent compressor damage. Signs of low refrigerant include ice on refrigerant lines, hissing noises, or weak airflow from vents. If you suspect a leak, don’t just “top it off”—it” needs to be found and fixed to avoid bigger issues down the road.
Refrigerant leaks often start over winter. The cold can cause small cracks in refrigerant lines due to metal contraction and expansion. If your system ran fine last summer but suddenly won’t start, a leak could have developed during the off-season. Also, if you suspect low refrigerant but your AC won’t turn on, check the refrigerant lines. If you see ice forming shortly after startup, your levels may be low. But if the system won’t start at all, it could be in low-pressure lockout mode—designed to protect the compressor.
Reason 4. Сonsequences of winter
Winter can be brutal on outdoor units. Ice and snow buildup can bend coil fins, water can freeze inside components, and rodents looking for warmth may have chewed through wiring. A quick inspection before startup can reveal problems: Look for physical damage, check for loose or frayed wires, and clear any debris. If your unit hums but doesn’t start, or you smell burning, stop immediately—something may have shorted out over the winter.
Beyond obvious snow and ice damage, lesser-known problems winter can cause are contactor freeze-up, pest-triggered short circuits, or nests in the fan blades. The contactor is like the “on/off switch” for your AC’s compressor. Moisture from snow or rain can cause it to corrode or stick. If your AC makes a faint click but doesn’t start, this might be the issue. Mice and squirrels love to chew wiring over winter. If your AC trips the breaker immediately upon startup, a chewed wire could be grounding out. Birds or squirrels might have built nests in your outdoor fan over winter. If the fan motor is jammed, the system won’t start. A quick visual inspection can save you from burning out the motor.
What does AC maintenance include? Steps before turning AC on
Pre-season checklist includes:
- Check and replace the air filter (dirty filters cause performance issues).
- Inspect and clean the outdoor unit (remove leaves, dirt, and debris). Over winter, algae or mold can grow inside the drain line. A quick flush with vinegar or compressed air can prevent clogs and leaks.
- Check the circuit breaker and thermostat settings (ensure power is on and settings are correct).
- Look for visible signs of damage (frayed wires, rust, leaks).
- Vacuum the evaporator coil. Dust buildup inside your indoor unit can cause efficiency problems.
- Some older AC units require periodic oiling to keep the fan motor running smoothly.
- Run a short test cycle (turn the AC on and listen for odd noises or weak airflow). Run your AC for at least 10 minutes on a cool day before you actually need it.
If everything seems fine but the AC won’t start or runs poorly, further troubleshooting may be needed.
When to Call a Pro for AC Repairs
If you’ve checked the power, thermostat, filter, and unit for visible issues but your AC still won’t start—or if it runs but struggles to cool—it’s time to call an expert. You should also bring in a professional if you notice strange noises (buzzing, clicking, or grinding), burning smells (could indicate electrical failure), repeated breaker trips (a sign of an underlying electrical issue), ice buildup on refrigerant lines (could mean a leak or airflow problem), warm air instead of cool air (could point to compressor or refrigerant issues).
