It’s the middle of July, temperatures outside are pushing 95, and your AC just stopped working. The first instinct is to call for help immediately — but before you do, there are a few simple checks that can save you a service call, a few hours of waiting, and sometimes a few hundred dollars.
Some AC emergencies aren’t emergencies at all. Others are. Here’s how to tell the difference fast.
At a Glance
- Start with the thermostat: wrong settings are one of the most common causes of AC problems
- A tripped circuit breaker can shut down your system and take 30 seconds to fix
- A clogged air filter can cause your AC to freeze up or shut off entirely
- If the unit is running but not cooling, the problem may be with the refrigerant or the outdoor condenser
- Know when to stop troubleshooting and call a licensed HVAC technician
Troubleshooting Your AC: Step-by-Step
Before you pick up the phone, work through these five checks in order. Each one takes just a few minutes, and together they’ll tell you whether you’re dealing with a quick fix or a job for a licensed technician.
Step 1: Check Your Thermostat Settings
Before anything else, walk over to your thermostat and take a look.
Make sure it’s set to COOL, not HEAT or FAN ONLY. It sounds obvious, but accidental mode changes happen, especially with smart thermostats or programmable schedules. While you’re there, confirm the set temperature is actually lower than the current room temperature. If the thermostat thinks it’s 72° and you want 74°, the system won’t run.
Also, check the batteries. A thermostat with dead or dying batteries may display correctly, but fail to send the signal that kicks on your system.
If you have a smart thermostat, check whether a scheduled away mode or vacation setting is active. These can override your manual input and prevent cooling from starting.
Step 2: Check the Circuit Breaker
Your air conditioner draws a significant amount of power — especially when starting up on a hot day. A sudden power spike or a system issue can trip the breaker, cutting power to the unit without any obvious warning.
Go to your electrical panel and look for any breakers that appear tripped (partially in the middle position, or flipped to the off side). The breaker for your AC unit is typically labeled something like “AC,” “HVAC,” or “Air Handler.”
If it’s tripped, switch it fully to OFF and then back to ON. Wait a few minutes before trying to restart your AC — most systems have a built-in delay of 2 to 5 minutes before they’ll start up again after a power interruption. According to the U.S. Department of Energy, this reset period protects the compressor from damage.
Important: if the breaker trips again shortly after resetting, stop and call a professional. A recurring trip means something in the system is drawing more power than it should, which needs diagnosis — not another reset.
Step 3: Check (and Replace) the Air Filter
A clogged air filter is one of the most common causes of AC problems in Colorado homes, and it’s also the most preventable. When the filter gets blocked, airflow through the system drops, and the evaporator coil can ice over. A frozen coil means no cooling — and if the system keeps running in that state, it can lead to compressor damage.
Find your filter (usually in the return air vent or inside the air handler cabinet) and pull it out. If you can’t see light through it, it needs to be replaced. A standard 1-inch filter should be replaced every 1 to 3 months, depending on how much you run your system and whether you have pets.
If the filter was clogged and you replace it, give the system an hour or two before restarting. This allows any ice on the coil to melt. Running the system while the coil is frozen won’t help — and it can make the situation worse.
Step 4: Check the Outdoor Unit
Head outside and take a look at your condenser unit — the large box with fins that sits outside your home.
Make sure the fan is running. If it isn’t spinning when the AC is supposed to be on, that’s a sign of a problem that typically needs professional attention.
You will also want to check for obvious blockages. Grass clippings, dirt, leaves, and debris can pack against the condenser fins and restrict airflow, making your system work harder and cool less efficiently. If there’s debris, turn the system off and gently clear it away. You can also rinse the fins with a garden hose from the inside out, but do not use a pressure washer.
Keep at least two feet of clearance around the unit at all times. According to ENERGY STAR, proper airflow around the condenser is one of the most important factors in system efficiency and longevity.
Step 5: Look for Ice on the System
If your system is running but blowing warm air or barely moving air at all, ice buildup could be the culprit. Check the refrigerant lines: the copper pipes connected to the outdoor unit, and the indoor air handler for frost or ice.
If you see ice, turn the system off and switch the thermostat fan to ON only (not COOL) to let the ice melt. This can take one to several hours. Once the ice is cleared, replace the filter if it was clogged, restore airflow, and try restarting.
If the system ices over again, the problem is likely low refrigerant or a failing component. That’s not a homeowner fix. Refrigerant handling requires EPA certification, and adding refrigerant to a leaking system without repairing the leak is both ineffective and against federal regulations.
When to Call SAC Mechanical
If you’ve worked through this checklist and your AC still isn’t cooling your home, it’s time to call a professional. SAC Mechanical provides emergency AC service to homeowners across Longmont and the surrounding Colorado communities.
Some problems — refrigerant leaks, failed capacitors, failing compressors, and electrical issues — can’t be diagnosed or repaired without the right tools and licensing. Attempting to fix them without training can void your warranty, damage the system further, or create a safety hazard.
The good news is that most real AC emergencies are diagnosable quickly by an experienced technician. If your system is older and repairs are becoming more frequent, it may also be worth asking about AC replacement options — a newer, properly sized unit can reduce your cooling costs and eliminate reliability problems that keep coming back.
A Quick Recap
Here’s the checklist at a glance:
- Thermostat: set to COOL, temperature below current room temp, batteries good, no away/vacation mode active
- Breaker: check for a tripped breaker, reset once if tripped, stop if it trips again
- Air filter: replace if clogged, let the coil thaw before restarting
- Outdoor unit: fan running, no debris blocking the condenser, at least two feet of clearance
- Ice: if present, switch to fan-only mode and let it melt completely before restarting
When in doubt, call SAC Mechanical. A quick professional diagnosis is always better than guessing — especially when Colorado summer temperatures don’t leave much room for error.