My AC Won’t Turn On: Troubleshooting Before You Call a Technician
My AC Won’t Turn On: Troubleshooting Before You Call a Technician When your AC system won’t turn on at all — no fan, no compressor, no response to thermostat changes — the cause is either an interruption in the electrical supply reaching the system (tripped breaker, blown fuse, safety switch activation, thermostat failure) or a failure of a startup component within the system itself (dead capacitor, burned contactor, failed control board, or seized compressor). About 30% of “AC won’t start” calls that Coastal Carolina Comfort responds to across South Carolina are resolved by the homeowner checks described below. The remaining 70% require professional diagnosis and repair. Coastal Carolina Comfort provides same-day diagnostic service for systems that won’t start across Summerville, Charleston, Columbia, and the entire Lowcountry and Midlands. Our NATE-certified technicians carry the common startup components — capacitors, contactors, control boards — needed to restore your system in a single visit. Call (843) 708-8735. Homeowner Troubleshooting: 6 Checks Before You Call These checks are safe for any homeowner to perform and take less than 10 minutes total. Work through them in order. Check 1: Thermostat Power and Settings Start at the thermostat — it’s the most common cause of a system that appears dead. Verify it has power. If the display is blank, the thermostat has lost power. Check whether it uses batteries (replace them) or is wired to the system (a tripped breaker or blown fuse at the air handler may have cut power to the thermostat). Verify the settings. Ensure the system is set to “cool” (not “off,” “heat,” or “fan only”), the set temperature is at least 3–5°F below the current room temperature, and any scheduling or away modes aren’t overriding your settings. Try a hard reset. Turn the thermostat completely off, wait 30 seconds, then turn it back to cooling mode. For smart thermostats, a power cycle or factory reset can resolve software glitches that prevent the system from responding. If the thermostat appears to be working correctly — display is on, settings are correct, it shows “cooling” — but the system doesn’t respond, the issue is downstream. Check 2: Circuit Breakers Your AC system typically uses two circuit breakers in your main electrical panel: one for the indoor air handler and one for the outdoor condenser unit. Check both. Look for a tripped breaker. A tripped breaker sits in the middle position — not fully “on” and not fully “off.” Push it firmly to “off” first, then back to “on.” If the breaker holds and the system starts, monitor it. If the breaker trips again within minutes, do not reset it a third time — the system has an electrical fault that requires professional diagnosis. Check for a blown fuse at the air handler. Some air handlers have a small fuse (typically 3–5 amp) on the control board that protects the low-voltage circuit. If this fuse blows, the thermostat loses its ability to communicate with the system. This fuse is accessible inside the air handler’s front panel — but if you’re not comfortable opening the panel, skip this check and call for service. Check 3: Emergency Shutoff Switch Many AC installations include a wall-mounted emergency shutoff switch that looks like a standard light switch — typically located near the indoor air handler or in the utility closet. If someone accidentally flipped this switch off (during maintenance, painting, or cleaning), the entire system is disabled. Check for a switch near the air handler that might be in the “off” position. Flip it on and see if the system responds. Check 4: Condensate Drain Safety Switch Many South Carolina HVAC installations include a float switch on the condensate drain line that shuts the system down when the drain line clogs and water backs up. This is a safety feature designed to prevent water damage — but it also means a simple drain clog can make your entire AC system unresponsive. If your system has a visible float switch on the drain line (a small device with a float attached to the PVC pipe near the air handler), check whether standing water is visible in the drain pan. If the pan is full, the float switch has activated. Clearing the drain line may restore system operation. Our guide on AC leaking water inside your house covers drain line clearing in detail. Check 5: Outdoor Disconnect Box Near your outdoor condenser unit, there’s a disconnect box — a small metal box mounted on the wall within a few feet of the unit. This box contains either a pull-out fuse block or a breaker that supplies power specifically to the outdoor unit. Check that the disconnect is in the “on” position and that the fuses (if applicable) haven’t blown. A blown disconnect fuse is a common cause of a system where the indoor fan runs but the outdoor unit doesn’t respond at all. Check 6: Wait 5 Minutes After Any Reset Modern AC systems have built-in time delays that prevent the compressor from restarting too quickly after a shutdown — rapid cycling can damage the compressor. If you’ve reset a breaker, flipped a switch, or changed the thermostat, wait at least 5 minutes before concluding the system isn’t responding. The delay is protecting your equipment. If the Homeowner Checks Don’t Work: Common Professional Repairs When all homeowner-accessible checks fail to restore the system, one of these mechanical or electrical failures is typically the cause. Failed Capacitor The run capacitor provides the electrical boost the compressor and fan motors need to start. When it fails, the motors can’t overcome their starting inertia. You might hear a clicking sound from the outdoor unit as the contactor engages, followed by a hum and then silence — the system is trying to start but the capacitor can’t deliver. Capacitor failure is the single most common reason an AC system won’t start. It’s also one of the most affordable repairs: $150–$300 including parts and labor. In South Carolina’s long cooling season, capacitors endure more
Why Is My AC Running But Not Cooling the House?
Why Is My AC Running But Not Cooling the House? When your AC runs continuously but your home isn’t reaching the set temperature, the system is either failing to produce adequate cooling or losing that cooling before it reaches your living spaces. The most common causes are low refrigerant charge from a leak, a dirty evaporator or condenser coil restricting heat transfer, leaking ductwork that dumps conditioned air into unconditioned spaces, or a system that is undersized for your home’s actual cooling load. Coastal Carolina Comfort diagnoses why your AC isn’t cooling effectively across Summerville, Charleston, Columbia, and every community we serve in the South Carolina Lowcountry and Midlands. Our NATE-certified technicians identify the root cause — not just the symptom — and provide upfront pricing before any repair begins. Call (843) 708-8735. First: Understanding the Difference Between “Not Cooling” and “Blowing Warm Air” These two problems overlap but aren’t identical, and the distinction affects the diagnostic path. AC blowing warm air means the air from your vents is noticeably warm — room temperature or warmer. This typically points to a complete failure of the cooling cycle: dead compressor, severely depleted refrigerant, tripped outdoor breaker, or a heat pump stuck in heating mode. If this describes your situation, our guide on AC blowing warm air covers those specific causes. AC running but not cooling means the system produces some cool air — you can feel it at the vent — but your home never reaches the set temperature, or takes far too long to get there. The system runs for hours without cycling off. This is a subtler problem with a wider range of possible causes, and it’s what this article addresses. In South Carolina’s climate, the distinction matters more than in cooler regions. A system that’s “almost cooling” but falls 5°F short can leave your home at 80°F with 70% humidity — which feels miserable even though the AC is technically doing something. The 7 Most Common Reasons Your AC Runs But Doesn’t Cool 1. Dirty Condenser Coil (Outdoor Unit) The condenser coil is where your system releases the heat it absorbed from inside your home. When the coil’s aluminum fins become coated with dirt, pollen, grass clippings, or pet hair, heat transfer drops dramatically. Your system still runs — the compressor works, the fan spins, cool air reaches the vents — but the system can’t reject enough heat to keep up with the load. In South Carolina, condenser coils take a beating. Spring pollen coats them heavily by April. Summer storms blow debris into the fins. And the combination of heat and humidity creates ideal conditions for biological growth between the fins. This is one of the most common — and most fixable — reasons an AC runs all day without cooling adequately. A professional coil cleaning restores heat transfer capacity and is typically included in regular maintenance that prevents costly repairs. 2. Dirty or Restricted Evaporator Coil (Indoor Unit) The evaporator coil absorbs heat from your indoor air. When it becomes coated with dust, mold, or biological growth — which happens faster in South Carolina’s humidity than in drier climates — its ability to absorb heat decreases. The air passing over a dirty evaporator coil cools less effectively, which means the air reaching your vents is cooler than room temperature but not cold enough to overcome the heat gain in your home. A dirty evaporator coil also increases humidity in your home because the coil can’t properly dehumidify the air passing over it. This is why a home might be at 74°F but feel clammy and uncomfortable — the AC is partially cooling but failing to adequately remove moisture. Learn more about what South Carolina humidity does to your cooling system. 3. Low Refrigerant Charge A partially depleted refrigerant charge produces exactly this symptom — the system runs, cool air reaches the vents, but the cooling capacity isn’t enough to match the heat load. Unlike a completely empty system (which blows warm air), a slow leak creates a gradual decline in performance that homeowners often attribute to “the system getting old” or “it’s just really hot outside.” The temperature differential between the supply air and return air tells the story. A properly charged system in South Carolina should produce a 15–20°F differential. If your supply air is only 8–12°F cooler than your return air, low refrigerant is a prime suspect. 4. Ductwork Leaks This is the hidden culprit that no amount of AC repair will fix, because the AC itself is working correctly. If your ductwork has gaps, disconnected joints, or deteriorated flex connections — especially where it runs through an unconditioned attic — cooled air escapes before it reaches your rooms. In a Lowcountry attic during summer, ambient temperatures regularly exceed 140°F. A duct leak in that environment doesn’t just lose cooled air — it actively pulls superheated attic air into the duct system, warming the conditioned air as it travels to your vents. Ductwork problems are especially common in older homes across Summerville’s Historic District, Charleston’s peninsula, and Columbia’s Shandon and Forest Acres neighborhoods where original ductwork may be 30–50+ years old. 5. Undersized or Improperly Sized System If your AC system was sized incorrectly for your home’s actual cooling load, it will run continuously on hot days without ever reaching the set temperature. This is more common than you’d expect, particularly in South Carolina where cooling loads are exceptionally high. An undersized system literally cannot produce enough cooling capacity to overcome the heat gain from walls, windows, attic, and South Carolina’s relentless humidity. Oversized systems create a different problem — short cycling — but undersized systems simply run all day, every day, wearing themselves out faster and costing more to operate. Sizing problems are especially prevalent in new construction where builder-grade systems may have been selected for cost rather than performance, and in homes that have been renovated or had additions built without upgrading the HVAC system to match the increased square footage.