It is 98°F in Columbia and your AC is running — you can hear it, the outdoor unit is spinning — but your house will not cool down. This is one of the most stressful HVAC situations a homeowner faces, and it happens constantly in the Midlands every summer. Before you call anyone, there are a few things worth checking yourself. And if those don’t resolve it, this guide will help you understand what a technician is likely to find — and what it will cost.
Kaminer Heating and Cooling has been diagnosing and fixing this exact problem for Columbia homeowners since 1956. Here is what we see most often, in order of how commonly we encounter each cause.
Check These First — Before Calling Anyone
1. Clogged or Dirty Air Filter
A severely restricted air filter is the single most common reason an AC runs constantly without cooling effectively. When the filter is clogged, airflow through the system drops dramatically — the evaporator coil cannot exchange heat properly, the system runs longer, and in extreme cases the coil freezes solid, blocking all cooling entirely. Pull your filter right now. If it is grey, dark, or visibly matted with dust, replace it. Give the system 30–45 minutes after installing a clean filter before judging whether it has improved. In Columbia’s pollen-heavy, humid environment, filters should be changed every 1–2 months during peak cooling season.
2. Thermostat Set Incorrectly or Malfunctioning
Confirm the thermostat is set to COOL (not HEAT or FAN ONLY) and that the set temperature is actually below the current room temperature. If you have a smart thermostat, check whether it is in an “away” or “eco” mode that is holding the temperature higher than you expect. If the thermostat screen is blank, check the batteries. A malfunctioning thermostat can cause the system to run continuously without properly signaling the compressor — the fan blows but no cooling happens.
3. Tripped Breaker or Disconnect
Check your electrical panel for a tripped breaker on the AC or air handler circuit. A tripped breaker often means the system tried to start, drew too much current, and the breaker protected itself. Reset it once — but if it trips again immediately, do not reset it a second time. A repeatedly tripping breaker indicates an electrical problem (often a failing capacitor or compressor) that needs a technician, not a reset.
4. Condensate Drain Safety Switch Triggered
In South Carolina’s humidity, condensate drain lines clog frequently. Many Midlands HVAC installations include a float safety switch on the drain line that shuts the system down when the drain backs up — preventing water damage to your ceilings or floors. If your system suddenly stopped cooling and you notice standing water near the air handler or a wet drain pan, a clogged condensate line is likely. You can attempt to clear it with a wet-dry vac on the drain outlet, but a technician should inspect and flush the drain line properly.
5. Blocked or Dirty Outdoor Unit
Go outside and look at your condenser unit. Is the area around it clear? Grass, leaves, or shrubs pressing against the unit restrict airflow and significantly reduce its ability to expel heat. Make sure there are at least 18 inches of clearance on all sides. You can also gently rinse the coil fins with a garden hose from the inside out — do not use a pressure washer. A heavily fouled condenser coil can reduce cooling capacity by 20–30% on its own.
Causes That Require a Technician
If the five checks above did not resolve your problem, one of the following is almost certainly the cause. These all require a licensed HVAC technician — do not attempt to diagnose or repair them yourself.
6. Failed Capacitor
As covered in our AC repair cost guide, capacitors are the most common component failure in Columbia’s summer heat. A failed capacitor means the compressor or fan motor cannot start properly. The outdoor unit may hum loudly but not spin, or may short-cycle rapidly. This is a same-day fix in most cases — $150–$320 including the service call — and our trucks carry the most common capacitors for Columbia-area systems.
7. Low Refrigerant (Refrigerant Leak)
Refrigerant is the medium that actually absorbs heat from your home. When a system has a refrigerant leak, cooling capacity drops — often gradually. Early signs: the system runs longer than usual to reach setpoint, or the air coming from the vents feels less cold than it used to. Late signs: the system runs constantly and the house barely cools, or the evaporator coil ices over. A refrigerant leak requires locating the leak, repairing it, and recharging the system — it is never just a recharge. In Columbia, this repair typically runs $350–$1,200 depending on leak location.
8. Frozen Evaporator Coil
A frozen coil is a symptom, not a root cause. The coil freezes when airflow is severely restricted (dirty filter, blocked vents, or collapsed duct) or when refrigerant is low. If you see ice on the refrigerant lines running into your air handler, turn the system off immediately — running a frozen system damages the compressor. Set the thermostat to FAN ONLY to thaw the coil (2–4 hours), then turn cooling back on with a clean filter. If it freezes again, you have an underlying issue that needs a technician.
9. Dirty Evaporator or Condenser Coil
Both coils — the indoor evaporator and outdoor condenser — need to be clean to transfer heat effectively. The evaporator coil accumulates dust, mold, and debris over time (a byproduct of pulling humid air across its surface in South Carolina’s climate). A heavily fouled coil can reduce cooling capacity significantly. This is addressed during a professional tune-up — it is one of the key reasons twice-annual maintenance matters in the Midlands.
10. Failing or Failed Compressor
The compressor is the heart of your AC — it pressurizes the refrigerant that makes the entire cooling cycle work. A failing compressor may cause intermittent cooling, warm air from running vents, or the system refusing to start (with a loud hum from the outdoor unit). Compressor replacement is the most expensive AC repair ($1,200–$2,500), and on any system over 10 years old it almost always makes replacement the better financial decision. Kaminer will give you an honest assessment including both options with full cost transparency.
11. Reversing Valve Stuck in Heating Mode
If your home uses a heat pump (the dominant system type across Irmo, Lexington, Seven Oaks, and most Midlands communities built in the 1980s–2000s), there is a component called a reversing valve that switches the system between heating and cooling modes. If this valve sticks or fails, the heat pump may blow warm air in summer even though the system appears to be running normally. This is a less common failure but one we see regularly — especially in older heat pumps past the 12-year mark.
Why Columbia’s Summer Makes Everything Worse
Columbia, SC is literally marketed as “Famously Hot” — and for HVAC purposes, that matters. Every AC system is designed to maintain a temperature differential of approximately 20°F below the outdoor temperature. When Columbia’s heat index pushes above 105°F, that means your system is fighting to keep your home at 82–85°F even when working perfectly.
A system that kept your home at 74°F in May may genuinely struggle to get below 78°F in July — not because something is broken, but because the outdoor conditions have exceeded what the system was sized to handle. If your system runs constantly on the hottest days but your home holds around 78°F, it may be performing correctly.
If your home cannot hold 78°F when outdoor temperatures are 90°F — or if the system is running constantly at a temperature it would normally reach easily — there is likely a performance issue worth investigating.
AC not cooling in Columbia and need help now? Kaminer’s licensed Comfort Specialists are available 24 hours a day, 7 days a week — no after-hours surcharge, ever. Call (803) 888-4115 and we will give you an honest arrival window and flat-rate pricing before any work begins.
How to Prevent This Next Summer
- Schedule a spring tune-up in March or April — before Columbia’s heat arrives and before every HVAC company in the Midlands is fully booked. Kaminer’s tune-up includes coil cleaning, capacitor testing, refrigerant check, condensate drain flush, and a full system inspection.
- Change your filter every 4–6 weeks during peak cooling season — not every 3 months. South Carolina’s humidity and pollen load filters much faster than manufacturer recommendations designed for average climates.
- Keep the outdoor unit clear year-round — especially after storms and during spring when grass and weeds grow fast.
- Don’t ignore small warning signs — a system that takes longer to cool the house than it used to, unusual sounds, or rising energy bills without a change in usage are all early warning signs. Addressing them in spring costs far less than an emergency call in July.
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