We have been running our HVAC company in Upstate South Carolina for 45+ years, and the most common problem we get called for after winter is an AC that runs but will not blow cold air.
After thousands of these calls across Greenville, Anderson, and the surrounding counties, we have narrowed the cause to 14 specific problems. Some are simple fixes homeowners can make, such as a clogged filter, a thermostat set to the wrong temperature, or debris blocking the outdoor unit. Others are bigger issues that require an HVAC technician, like a refrigerant leak, a failed capacitor, or a compressor on its last cycle.
In this guide, we’ll walk you through the 14 causes in the order our technicians check them on every service call. You will learn how to recognize each one, what to do next, and when the problem crosses the line from a DIY fix to a job that needs a professional.
Common Causes of an AC Not Blowing Cold Air
The list below walks through every cause in the order our technicians check them on a service call. We start with the fastest and easiest checks, then move on to problems that require diagnostic tools, and finish with component failures that might require a full repair or replacement.
1. The Thermostat Is Set Incorrectly
The thermostat is the first thing our technicians check on every service call, and it causes more “my AC isn’t working” complaints than any other single issue. Most of the time, the fix takes under two minutes and costs nothing.
Walk to your thermostat and check three settings. Your thermostat mode should be set to Cool, not Heat or Off. The fan should be set to Auto, not On. The target temperature should be at least 5°F below the current room temperature.
The Auto versus On setting trips up more homeowners than any other. When the fan is set to On, the blower runs continuously and pushes air through the vents even when the system is not actively cooling. That air feels warm because it is just room-temperature air being circulated. Switch the fan to Auto, and the blower will run only when the system is actively cooling, so the air coming from the vents will actually feel cold.
If your thermostat screen is blank or dim, the batteries are dead. Most thermostats use two AA or AAA batteries and take under a minute to replace. Do this every spring as part of your seasonal maintenance, even if the display still looks fine.
2. The Air Filter Is Clogged
A clogged air filter is the single most common cause of reduced cooling performance we see in Upstate homes. When the filter becomes clogged with dust, pollen, and pet dander, airflow across the evaporator coil decreases. Less airflow means less heat transfer, which means the air coming out of your vents feels warm or only slightly cool.
Pull the filter out and hold it up to a light. If you cannot see light through it, replace it. A new filter costs between $5 and $20 at any hardware store, and the swap takes under a minute.
Filter cadence matters more in the Upstate than in most of the country. Pollen season in Greenville, Greer, and Anderson runs heavy from March through October, and it loads filters faster than the national average. We recommend checking filters monthly during those months and replacing them every 30 to 60 days. Outside of pollen season, every 60 to 90 days is usually enough.
One warning on filter selection. High-MERV filters trap more particles but also restrict airflow more. If you upgrade to a MERV 13 or higher filter without checking your system’s specs, you can actually reduce cooling performance. A MERV 8 to 11 filter is the right range for most residential systems.
Regular filter changes are one of the easiest parts of HVAC preventative maintenance, and they prevent a long list of more expensive problems later.
3. Supply or Return Vents Are Closed or Blocked
Your AC needs a clear path for air to flow through every room in the house. When supply vents are closed or blocked, cold air cannot reach the rooms that need it. When return vents are blocked, the system cannot draw warm air back to the evaporator coil for cooling.
Walk through every room and check both types of vents. Supply vents are the ones that blow cold air out. Return vents are larger, usually on a wall or ceiling, and pull air back to the system.
Make sure every vent is fully open. Move furniture, rugs, and curtains off of any vent that has something in front of it. Open interior doors to bedrooms or rooms that consistently feel warmer than the rest of the house.
A common mistake we see in Upstate homes is closing vents in unused rooms to save energy. This increases pressure in the duct system, reducing overall efficiency and potentially causing the evaporator coil to freeze over time. Leave every vent open, even in rooms you do not use often.
4. Debris Is Blocking the Outdoor Condenser Unit
The outdoor AC unit needs to release heat into the surrounding air. When the coil fins are coated with grass clippings, pollen, leaves, or dirt, the unit cannot dump heat efficiently. The result is warm air at the indoor vents even though the system is running.
Shut the power off at the outdoor disconnect box before you touch the unit. Clear any branches, leaves, or grass that have built up against the sides. Trim back any plants or shrubs within two feet of the unit on all sides. Spray the coil fins gently with a garden hose, aiming the water at a 45-degree angle from the inside out if you can access the top. Never use a pressure washer because the coil fins bend easily and restrict airflow once damaged.
Spring cleanup in Upstate South Carolina is rough on outdoor units. Pine straw, oak pollen, and grass clippings from early mowing season pack into the fins faster here than in most parts of the country.
A five-minute hose rinse every spring before the first hot stretch prevents a service call later in the summer. For units with heavy buildup, a professional AC coil cleaning restores airflow and cooling capacity.
5. The Circuit Breaker Tripped
A central AC draws enough power that a tripped breaker will shut down either the outdoor unit, the indoor blower, or both. When only the outdoor unit loses power, the indoor fan keeps running and pushes room-temperature air through the vents, which is the exact symptom of an AC that “runs but does not blow cold air.”
Open your electrical panel and look for any breaker in the middle position or flipped to Off. Most AC systems have two breakers, one for the outdoor condenser and one for the indoor air handler.
Flip the tripped breaker fully to the Off position, wait 60 seconds, then flip it back to On. Walk to the thermostat and wait 30 minutes before expecting cold air, since most systems have a built-in delay that protects the compressor from short-cycling.
If the breaker trips a second time, do not keep resetting it. A breaker that trips repeatedly points to a short circuit, a failing capacitor, a compressor drawing too much current, or a wiring problem. Each of those issues worsens each time the system tries to start.
Shut the thermostat off, leave the breaker off, and call an HVAC technician.
6. The Outdoor Disconnect Switch Is Off
Every outdoor AC unit has a disconnect box mounted on the wall within a few feet of the condenser. The box contains a switch or pull-out that cuts power to the outdoor unit for safety during service work. When the switch is accidentally flipped, the outdoor unit stops running, and cold air stops reaching the house.
Walk to the outdoor unit and find the gray metal box on the wall nearby. Open the cover. Some disconnects have a flip switch, while others have a pull-out block that needs to be inserted in the correct orientation. Make sure the switch is in the On position or the pull-out is fully seated with the arrow pointing up.
We see this more often than homeowners expect. Landscapers, pest control technicians, and anyone working near the outdoor unit sometimes flip the disconnect for safety and forget to turn it back on. It is worth checking before you assume the system has a deeper problem.
7. The Condensate Drain Line Is Clogged
As your AC cools the air in your home, it also pulls moisture out of it. That moisture collects on the evaporator coil, drips into a pan below, and drains outside through a white PVC pipe called the condensate drain line. When the line clogs with algae, dirt, or biofilm, water backs up into the drain pan. Most modern systems have a float switch that shuts off the AC when the pan fills up, preventing the house from flooding and also stopping the cold air.
Check for signs of a clogged line. Look for water pooling around the indoor unit, a full drain pan, or a system that shuts off on its own after running for a few minutes. Find the outdoor end of the drain line, usually a white PVC pipe sticking out of the exterior wall near the outdoor unit. If no water is dripping from it on a humid day when the AC is running, the line is likely clogged.
You can try to clear it yourself with a wet/dry shop vac. Hold the vacuum hose against the outdoor end of the drain line, seal the connection with a rag, and run the vacuum for two to three minutes. Follow up by pouring a cup of distilled white vinegar down the indoor access port, which is usually a T-shaped fitting near the air handler. The vinegar kills algae and prevents the line from clogging again.
If the line clogs again within a few weeks, or if you cannot find the access points, call a technician. Recurring clogs often indicate an improper slope in the drain line or a larger biofilm issue within the system. A professional drain line cleaning costs between $75 and $250.
High summer humidity in Upstate South Carolina produces more condensate than drier climates. Drain lines here clog faster, which is why we include a condensate line flush in every spring tune-up.
8. The Evaporator Coil Is Frozen
The evaporator coil sits inside the indoor air handler and absorbs heat from the air passing over it. When airflow drops or refrigerant levels fall too low, the coil gets cold enough to freeze. Ice builds up on the coil and the copper lines running to the outdoor unit. Once the coil is frozen, cold air stops reaching the vents entirely.
Look at the refrigerant line where it connects to the indoor unit, which is the larger of the two copper lines wrapped in black foam insulation. If you see ice or frost on the line or the coil itself, the system is frozen.
Shut the AC off at the thermostat immediately. Running a frozen system can damage the compressor, the most expensive component in the unit. Set the fan to On without cooling to blow warm air across the coil and speed up the thaw. A full thaw takes anywhere from 4 to 24 hours, depending on how much ice has accumulated.
A one-time freeze often stems from a dirty filter or closed vents, both of which you can fix yourself. If the coil freezes again within a few days of the thaw, the cause is deeper. Low refrigerant from a leak, a failing blower motor, or a dirty evaporator coil all require an HVAC technician to diagnose. Mini-split owners seeing similar symptoms can also check our guide on why your split AC is not cooling while the fan is running.
A service call for a recurring freeze typically runs $150 to $400 for diagnosis, plus any parts or refrigerant needed to fix the underlying issue.
9. The Refrigerant Is Low Due to a Leak
Refrigerant is the chemical that moves heat from inside your house to outside. If refrigerant levels are low, there is a leak somewhere in the system. A leaking AC blows warm or only slightly cool air because the refrigerant cannot absorb enough heat from the indoor coil.
Start at the indoor unit and listen for a hissing or bubbling sound near the copper lines, which is refrigerant escaping through a leak. Check the large copper line running from the indoor unit to the outside. If you see ice or frost forming on it, refrigerant levels are almost certainly low. You may also notice your electric bills climbing because the system runs longer to reach the same temperature, or warm air coming from the vents even with the thermostat set low.
This is not a DIY fix. EPA regulations require a certified technician to handle refrigerant, and simply adding more refrigerant without finding and repairing the leak wastes money and harms the environment. A technician will use an electronic leak detector, UV dye, or pressure testing to locate the leak, repair the line or fitting, then recharge the system to the correct level.
Expect to pay $200 to $600 for a recharge and a small leak repair. Larger leaks, damaged evaporator coils, or units using older R-22 refrigerant can increase costs. R-22 was phased out by the EPA in 2020, and refrigerant for older systems is now expensive and in limited supply. If your AC was installed before 2010 and needs a major refrigerant repair, the cost often makes replacement the better long-term option.
Upstate heatwaves push systems past their design load and reveal surface refrigerant leaks that would otherwise remain hidden in milder climates. We see more leak calls during July and August than at any other time of year.
10. The Evaporator or Condenser Coil Needs Deep Cleaning
Both coils in your AC play a direct role in moving heat. The evaporator coil inside the house absorbs heat from the indoor air. The condenser coil outside releases that heat into the outdoor air. When either coil gets coated with a layer of dirt, dust, or biofilm, the heat transfer drops and the system loses its ability to cool.
A surface rinse of the outdoor condenser coil with a garden hose is something you can do yourself. That handles loose debris on the fins’ outer surfaces. Deep cleaning requires disassembling parts of the unit, applying a specialized foaming coil cleaner, rinsing with controlled pressure, and straightening any bent fins with a fin comb. The evaporator coil is even harder to reach because it sits inside the sealed air handler cabinet.
The symptoms of coils that need deep cleaning include a system that runs constantly without reaching the setpoint, higher-than-normal electric bills, weak airflow at the vents, and a musty smell coming from the supply registers. The last symptom points specifically to the indoor coil, where moisture and dust combine to create biological growth.
A professional coil cleaning costs between $150 and $450, depending on coil access, the type of cleaner used, and whether both coils need service. We recommend a full coil inspection as part of every annual tune-up. Catching buildup early prevents coil corrosion, which eventually leads to refrigerant leaks and compressor failure.
11. The Capacitor Failed
The capacitor is a small cylindrical component inside the outdoor unit that stores and releases an electrical charge. Its job is to give the compressor and the outdoor fan motor the jolt of power they need to start up. When the capacitor weakens or fails, the motors struggle to start or cannot start at all. The outdoor unit hums or buzzes without actually running, and no cold air reaches the house.
You may hear a humming or buzzing sound from the outdoor unit with no fan movement. You may see the fan blade sitting still while the unit is supposed to be running. You may notice the fan starts slowly or only after you give it a push with a stick. You may find that the unit shuts off shortly after starting, then trips the breaker on the next attempt.
Do not attempt to replace a capacitor yourself. Capacitors store a lethal electrical charge even after the power to the unit is shut off, and discharging one incorrectly causes serious injury. This is a technician-only repair. A professional will safely discharge the old capacitor, test it with a multimeter to confirm failure, and install a replacement rated for your specific unit.
Capacitor replacement is one of the more affordable AC repairs, typically around $400 including parts and labor. A failing capacitor is also one of the most common causes of summer breakdowns in Upstate homes. Heat accelerates capacitor wear, which is why we include a capacitor test in every spring tune-up.
12. The Condenser Fan Motor Is Broken
The condenser fan sits on top of the outdoor unit and pulls air across the condenser coil to release heat. When the fan motor fails, the coil has no airflow, the refrigerant cannot dump its heat, and the system loses its ability to cool the house. A broken condenser fan motor also causes the compressor to overheat, which can lead to a much more expensive repair if the system keeps running.
Check the outdoor unit while the AC is supposed to be running. The top of the unit should have a fan blade spinning at a steady speed. If the blade is still, spinning slowly, or wobbling, the motor is failing. Another sign is a unit that feels unusually hot to the touch on top after 15 minutes of running.
This is not a DIY repair. Replacing a condenser fan motor requires accessing the wiring inside the unit, matching the correct motor specifications (horsepower, voltage, rotation direction, and shaft size), and verifying the capacitor is sized correctly for the new motor. A technician will also check whether a seized motor damaged the compressor or tripped internal safety switches.
Expect to pay between $300 and $900 for a condenser fan motor replacement, depending on the motor size and whether the capacitor needs to be replaced at the same time. A failing fan motor often takes the capacitor out with it, so pricing frequently covers both parts.
13. The Ductwork Is Leaky or Disconnected
Your AC can produce plenty of cold air, but if the ductwork that carries it to each room is leaking or disconnected, much of the cooled air ends up in the attic, crawlspace, or wall cavities instead of the living spaces. The Department of Energy estimates that the average home loses 20 to 30 percent of its conditioned air through duct leaks. In a system with a disconnected duct, the loss can be far higher.
Walk through the house on a hot afternoon with the AC running. Check the temperature in every room. If some rooms feel noticeably warmer than others despite having the vents open, you likely have a duct leak or a disconnected run. You may also notice your energy bills climbing without any other obvious cause, dust accumulating faster than normal, or warm air coming from the supply vents farthest from the air handler. The extra dust comes from unfiltered attic or crawlspace air getting pulled in through return-side leaks.
A visual inspection of accessible ducts, usually in an unfinished basement or attic, can reveal obvious disconnects or loose joints. Do not use household duct tape to seal anything you find. Despite the name, duct tape fails quickly to seal ducts under temperature swings and is not code-approved for duct sealing. Mastic sealant or foil-backed UL-181 tape are the correct materials, and they should only be applied after the ducts have been cleaned.
Professional duct sealing runs between $200 and $700 for accessible sections and common leak points. Full duct replacement on a system with widespread damage, undersized ducts, or poor original design can cost $2,000 to $6,000, depending on the size of the home. A technician can run a duct pressure test to measure exactly how much air is leaking and pinpoint the worst sections, which keeps the repair scope focused.
14. The Compressor Is Failing
The compressor is the heart of the AC system. It sits inside the outdoor unit and pressurizes the refrigerant, which allows it to absorb and release heat as it cycles through the system. When the compressor fails, the entire cooling cycle stops. The outdoor fan may still spin, and the indoor blower may still run, but the air coming from the vents never gets cold.
Stand near the outdoor unit while the AC tries to start. A failing compressor usually announces itself with loud clicking, grinding, or rattling sounds on startup, along with heavy vibration from the unit. You may also notice the outdoor unit repeatedly trips the breaker, or warm air coming from the vents, even though every other component looks fine. The breaker trips because the compressor draws too much current as it tries to start.
A failing compressor is a technician-only diagnosis and repair. The tools required to test compressor windings, measure amp draw under load, and recover refrigerant are not available at a hardware store. Even if you could replace the part, a compressor replacement requires evacuating and recharging the refrigerant, which EPA rules restrict to certified professionals.
Compressor repair costs between $1,000 and $2,000, depending on the specific failure and whether refrigerant needs to be replaced. A full compressor replacement costs $1,500 to $3,000 for most residential units and can exceed $3,500 for larger or higher-efficiency systems.
For any system over 10 years old, a failed compressor usually tips the math toward replacing the entire unit rather than repairing it. A new compressor on an aging system often fails again within a few years as the surrounding components continue to wear.
How to Prevent AC Cold-Air Problems
A system that gets looked after once a year rarely surprises its owner with a no-cool call in the middle of July. The checklist below covers the maintenance habits we recommend to every Air Today customer in the Upstate.
- Replace the air filter every 30 to 90 days. During heavy pollen months in the Upstate, which typically run from March through October, lean toward the shorter end of that range and check the filter monthly. A clean filter prevents frozen coils, reduced airflow, and early compressor wear.
- Schedule a professional tune-up every spring before the first 90°F day. Our technicians check refrigerant levels, clean both coils, test the capacitor, flush the condensate drain line, tighten electrical connections, and verify airflow across the system. Catching a weak capacitor or a slow refrigerant leak in April prevents a rushed service call in July.
- Rinse the outdoor coil with a garden hose at the start of every cooling season. Shut the power off at the disconnect, clear any debris built up against the unit, and spray the fins gently from the inside out. This five-minute task removes the pollen and grass clippings that would otherwise block airflow by mid-summer.
- Keep a two-foot clear zone around the outdoor unit year-round. Trim back any shrubs or plants growing toward the unit. Move lawn furniture, trash cans, and storage bins that collect near the condenser during winter.
- Pour a cup of distilled white vinegar down the condensate drain line access port once a month from May through September. The vinegar kills algae and biofilm before either can clog the line and shut the system down.
- Replace the batteries in your thermostat every spring, even if the display still looks fine. A thermostat that loses power mid-summer is easy to mistake for a larger system failure.
- Watch for early warning signs and call for service before a small issue becomes a major repair. Longer run times, higher electric bills, uneven room temperatures, or unusual sounds from the outdoor unit all point to a developing problem. Catching these signs early prevents a minor issue from escalating into a compressor replacement.
When to Repair vs. Replace Your AC
Some of the problems we mentioned above are straightforward repairs for any system. A clogged drain line, a dirty filter, or a failed capacitor rarely justifies replacing the whole unit. Other problems force a bigger decision, especially on systems that are getting older or have needed repeated repairs over the last few years.
The simplest way to weigh the decision is to multiply the system’s age by the cost of the proposed repair. If the result exceeds $5,000, replacement usually makes more financial sense than the repair. A 12-year-old system with a $450 capacitor and fan motor replacement comes in at $5,400, tipping the math toward replacement. A 6-year-old system facing the same repair comes in at $2,700, which makes the repair the obvious choice.
The US Department of Energy puts the average lifespan of a central AC system at 15 to 20 years. Systems in Upstate South Carolina tend to fall in the lower half of that range due to the long cooling season and the humidity load. If your system is more than 12 years old and has needed multiple repairs in recent summers, each new repair becomes a harder economic case.
A few specific repairs almost always tip the balance toward replacement on older systems:
- Compressor failure. A compressor replacement on a unit over 10 years old rarely delivers the return on investment it would on a newer system. The surrounding components continue to age at the same rate, and a new compressor on a tired system often fails again within a few years.
- Recurring refrigerant leaks. A single leak repair is worth doing. Multiple leaks within a few seasons usually mean the coil or the refrigerant lines are corroding throughout the system, and each new repair is temporary.
- Evaporator coil replacement on a pre-2010 system. Older systems that still use R-22 refrigerant face expensive coil and refrigerant costs. The EPA phased R-22 out in 2020, and the refrigerant is now costly and in limited supply.
SEER efficiency ratings have jumped since the federal minimum changes in 2015 and 2023, and a 15-year-old system running six months of cooling per year often pays back a new high-efficiency unit in five to seven years through lower electric bills alone. Replacement costs for a properly sized system in the Upstate typically range from $5,500 to $16,000, depending on tonnage, efficiency tier, and whether ductwork changes are needed.
When our Air Today technicians come out for a repair call, we give you an honest assessment of your system’s condition. If the repair makes sense, we provide a quote. We lay out both options in writing, explain the reasoning behind each one, and let you make the call.
Get Reliable AC Repair in Greenville and Upstate South Carolina
If your AC is running but not blowing cold air and the DIY checks did not solve the problem, our technicians can diagnose the issue and get your system cooling again.
We are a family-owned business and have been serving homeowners in Greenville, Greer, Simpsonville, Mauldin, Piedmont, Easley, Anderson, Clemson, and Seneca for over 45 years. Our technicians are EPA 608 certified, background-checked, and trained to walk you through the diagnosis before any repair begins.
Every service call comes with upfront pricing, a 100% satisfaction guarantee, and no pressure to replace a system that can still be repaired. Call us at (864) 295-0905 or contact us online to book a same-day or next-day appointment.