AC Not Cooling House: How to Fix It Today

Last updated: April 2026

By the HVAC Pricing Guide Team

Your AC is running but the house is getting warmer. Before calling anyone, check three things that resolve this problem 60% of the time: the air filter, the thermostat, and the outdoor unit. Here is how to diagnose the cause in the next 10 minutes.

This guide walks you through every reason an AC system stops cooling, starting with the simplest fixes you can do yourself right now and progressing to problems that require a professional. For complete repair pricing, see our AC repair cost guide. For an interactive step-by-step diagnosis tool, try our HVAC troubleshooter.

What Should You Check First?

Three simple checks resolve the majority of "AC not cooling" calls before a technician is ever needed. Work through these in order. Each takes less than 3 minutes.

Check 1: The air filter

The air filter is the single most common reason an AC system stops cooling effectively. The filter is a rectangular frame (usually 1 inch or 4 inches thick) located inside the return air grille on a wall or ceiling, or inside the air handler or furnace cabinet where the large return duct connects. Pull the filter out and hold it up to a light source. If you cannot see light passing through the filter material, the filter is clogged and restricting airflow severely enough to impair cooling.

A clogged filter starves the evaporator coil (the indoor component where refrigerant absorbs heat from your home's air) of the airflow it needs to function. Without adequate airflow, the coil gets too cold, ice forms on the coil surface, and the system's cooling output drops dramatically. Replace the filter immediately with the same size. Filter sizes are printed on the frame of the existing filter. Standard 1-inch filters cost $5 to $15 at any hardware store. If you do not have a replacement on hand, running the system with no filter for a few hours while you get a new one is better than running it with a completely clogged filter, though this is only a temporary measure because running without a filter allows dust to coat the evaporator coil over time.

After replacing the filter, give the system 30 to 60 minutes to recover. If the evaporator coil was beginning to ice over from restricted airflow, it may take longer to return to normal cooling. If the system still is not cooling after an hour with a clean filter, move to Check 2.

Check 2: The thermostat

The thermostat is the wall-mounted control device that tells the AC system when to run and at what temperature. Thermostat issues cause more unnecessary service calls than any other single factor. Verify the following settings in this exact order.

First, check the mode. The thermostat must be set to COOL, not HEAT, not OFF, and not FAN ONLY. It sounds obvious, but accidental mode changes (bumped by a child, changed during a power outage, toggled during seasonal transition) are extremely common. Second, check the temperature setting. The set temperature must be at least 3 to 5 degrees below the current room temperature displayed on the thermostat. If the set temperature is higher than the room temperature, the system has no reason to produce cooling. Third, check the batteries. Many thermostats run on AA or AAA batteries, and when those batteries die, the thermostat may display a blank screen, show erratic readings, or lose its programmed schedule. Replace the batteries if you cannot remember the last time you changed them. Fourth, check the fan setting. The fan should be set to AUTO, not ON. When the fan is set to ON, the blower runs continuously even when the compressor is not running, which means the system blows room-temperature air between cooling cycles. This makes it feel like the AC is running but not cooling, when in reality the compressor is cycling normally but the fan is blowing uncooled air during the off cycles.

If your thermostat is a programmable or smart model, verify that the schedule has not reverted to a default program or been changed inadvertently. Some smart thermostats enter "away" or "eco" mode based on occupancy sensors, raising the set temperature when they think nobody is home. Check the app or the thermostat screen for any active modes that override your preferred temperature.

Check 3: The outdoor unit

The outdoor unit (also called the condenser or condensing unit) is the large metal box sitting outside your home, usually on a concrete pad next to the house or on the rooftop. Walk outside and look at it while the system is running. Answer three questions.

Is the fan spinning? Look at the top of the unit. You should see a fan blade spinning and feel warm air blowing upward. If the fan is not spinning, the capacitor (a cylindrical component that stores electrical energy to start the fan motor and compressor) has likely failed, or the fan motor itself has failed. If the fan is not spinning but you hear a humming sound, the capacitor is the most likely cause. Do not let the system continue to run with the fan not spinning, because the compressor will overheat and sustain permanent damage within 30 to 60 minutes. Turn the system off at the thermostat.

Is the unit clear of debris? Leaves, grass clippings, dirt, cottonwood seed, and other debris can coat the condenser coil fins and block airflow. The outdoor unit needs at least 2 feet of clearance on all sides to draw in adequate air. If bushes, fencing, or stored items are pressed against the unit, the condenser cannot release heat properly and the system's cooling output drops significantly. Clear any debris and trim vegetation back to at least 2 feet.

Is the unit running at all? If the outdoor unit is completely silent and nothing is running, check your electrical panel for a tripped breaker. AC systems typically have two breakers: one for the indoor air handler or furnace, and one for the outdoor unit. If the outdoor unit breaker has tripped, flip it fully to the OFF position, wait 30 seconds, then flip it back to ON. If it trips again immediately, there is an electrical fault and you should leave the breaker off and call a technician. Do not keep resetting a breaker that trips repeatedly, as this can cause a fire.

What Does It Mean If There Is Ice on Your AC?

Ice forming on your AC system is one of the most common reasons a system stops cooling, and it is also one of the most misunderstood. You may see ice or frost on the copper refrigerant lines (the two copper pipes running between the indoor and outdoor units, usually wrapped in black foam insulation), on the outdoor unit itself, or on the indoor evaporator coil if you can see it inside the air handler cabinet. Ice on any of these locations means the evaporator coil temperature has dropped below 32 degrees, which should not happen during normal operation.

Why ice forms on an AC system

Ice formation has three primary causes. The first and most common is restricted airflow from a dirty filter. When the filter is clogged, insufficient warm air passes over the evaporator coil, so the coil temperature drops below freezing and moisture in the air freezes on the coil surface. The ice layer further blocks airflow, which makes the coil even colder, creating a cycle that continues until the coil is completely encased in ice and virtually no air passes through. The second cause is low refrigerant from a leak. When the refrigerant charge (the amount of refrigerant chemical circulating in the system) is low, the pressure inside the evaporator coil drops, which causes the coil temperature to fall below freezing even with normal airflow. The third cause is blocked or closed supply vents inside the house. If too many vents are closed, the airflow across the evaporator coil is reduced the same way a dirty filter reduces it, and ice forms.

What to do when you find ice

Turn the system OFF at the thermostat immediately. Do not try to chip or scrape ice off the coil or refrigerant lines. Set the thermostat fan setting to ON (not AUTO). This runs the blower fan continuously, circulating warm room air across the frozen coil to melt the ice gradually. Replace the air filter if it is dirty. Open all supply registers and return air grilles throughout the house. Wait 4 to 6 hours for the ice to melt completely. You may see water dripping from the air handler as the ice melts. Place towels around the base of the air handler to catch any overflow if the drain pan cannot handle the volume.

After the ice has fully melted, turn the system back to COOL and monitor it for 2 to 4 hours. If the system cools normally and no ice returns, the cause was likely the dirty filter or closed vents, and you have solved the problem. If ice forms again within 24 hours even with a clean filter and all vents open, the system is low on refrigerant, which means there is a leak that requires a professional to locate and repair. See our refrigerant recharge cost guide for what to expect when a technician addresses a refrigerant leak.

How long the thaw process takes

A lightly iced coil may thaw in 2 to 3 hours. A heavily iced coil (solid block of ice around the coil and suction line) can take 6 to 8 hours or longer. Do not try to speed the process with a hair dryer, heat gun, or hot water, as rapid temperature changes can crack the copper tubing or damage the coil fins. Patience is required here. Running the system before the ice has completely melted will cause the ice to reform almost immediately.

Why Is Your AC Blowing Warm Air?

If warm air is actively blowing from your vents while the AC is set to COOL, the blower fan is working but the cooling system itself is not. This narrows the possible causes to a handful of specific failures.

Compressor not running

The compressor is the pump inside the outdoor unit that circulates refrigerant through the system. When the compressor fails, the blower fan inside still pushes air through the ductwork, but that air passes over an evaporator coil that has no cold refrigerant flowing through it, so the air comes out at room temperature or slightly warm. A failed compressor can be caused by a bad capacitor (the compressor needs the capacitor to start), a failed contactor (the electrical switch that sends power to the compressor), internal mechanical failure of the compressor itself, or a safety switch that has shut the compressor down due to high pressure or high temperature. Compressor-related repairs range from $150 to $350 for a capacitor to $1,500 to $3,000 for a full compressor replacement. See our compressor replacement cost guide for the detailed breakdown.

Refrigerant leak

Refrigerant is the chemical compound (R-410A in most systems manufactured after 2010, R-22 in older systems) that absorbs heat from indoor air and transfers it outside. In a properly sealed system, refrigerant never runs out. If the system is low, there is a leak somewhere in the refrigerant circuit, typically at a brazed joint, a valve fitting, or within the evaporator or condenser coil itself. A system with a significant refrigerant leak blows air that feels cool but not cold at first, then progressively warmer as the charge drops. A technician uses pressure gauges and electronic leak detectors to locate the leak. Repair costs depend on the leak location: $200 to $500 for an accessible joint repair, $800 to $1,500 for a coil leak that requires component replacement, plus $200 to $700 for the refrigerant recharge. Our evaporator coil cost guide covers the full pricing if the coil itself is leaking.

Electrical issue

Several electrical failures can stop the compressor from running while the blower continues. A tripped breaker to the outdoor unit cuts power to the compressor but the indoor blower (which runs on a separate circuit) keeps running. A failed contactor prevents power from reaching the compressor even though the control signal from the thermostat is working correctly. A blown fuse on the disconnect box near the outdoor unit stops all power to that unit. A failed control board in the air handler may not send the signal to the outdoor unit to start. Check the breaker panel and the outdoor disconnect box (the small metal box mounted on the wall near the outdoor unit, usually with a pullout handle) before calling a technician. The capacitor replacement costs $150 to $350, and the contactor replacement costs $150 to $375. See our capacitor replacement cost guide for more detail.

Why Is Your AC Blowing Cool Air but Not Cold Enough?

This is different from warm air. The system is producing some cooling, the air from the vents feels cooler than room temperature, but the house will not reach the set temperature and the system runs constantly. There is a meaningful difference between a system that produces no cooling (see the warm air section above) and a system that produces inadequate cooling. The causes are different.

Low refrigerant (partial leak)

When the refrigerant charge is slightly low rather than severely low, the system still produces some cooling but at reduced capacity. The air from the vents might be 10 to 12 degrees cooler than the return air instead of the normal 15 to 20 degrees. The system runs much longer than usual to maintain the set temperature and may not reach it at all during the hottest part of the day. A technician measures the refrigerant pressure with gauges connected to the service ports on the outdoor unit. If the charge is low, they locate and repair the leak, then add refrigerant to bring the charge back to the manufacturer's specification. The cost for leak detection, repair, and recharge typically runs $400 to $1,200.

Dirty condenser coil

The condenser coil is the set of aluminum fins wrapped around the inside perimeter of the outdoor unit. Its job is to release the heat that the refrigerant absorbed from your indoor air. When the coil fins are caked with dirt, pollen, grass clippings, or cottonwood seed, the coil cannot release heat efficiently. The result is reduced cooling capacity and higher energy bills. You can often see the buildup by looking at the coil through the side grille of the outdoor unit. If the fins are visibly coated, the coil needs cleaning. You can gently rinse the coil with a garden hose from the inside out (spraying outward through the fins) to remove surface debris. Do not use a pressure washer, as high pressure bends the delicate fins and makes the problem worse. For heavily soiled coils, a professional cleaning with specialized coil cleaner costs $100 to $250. Regular condenser cleaning is covered in our AC repair cost guide.

Failing compressor

A compressor in the early stages of failure may still run but at reduced output. It struggles to build adequate pressure, and the system produces less cooling than it should. Signs of a failing compressor include the system taking much longer to reach the set temperature than it used to, the outdoor unit making a louder than normal humming or vibrating sound, and the circuit breaker tripping occasionally but not every time. A technician measures the compressor's amperage draw and compares it to the rated full-load amps on the unit's data plate. A compressor drawing significantly more than rated amps is working harder than it should and approaching failure. At this stage, you should get a quote for compressor replacement ($1,500 to $3,000) and a quote for full system replacement to compare. If the system is over 10 years old, replacement usually makes more financial sense. Our when to replace guide covers the decision framework in detail.

Extreme outdoor heat

This is not a malfunction. Residential AC systems are designed to maintain a 20 to 25 degree temperature differential (sometimes called delta T) between outdoor and indoor temperatures. On a 100-degree day, maintaining 75 to 80 degrees indoors is normal operation. On a 110-degree day, maintaining 85 to 90 degrees indoors may be the system's maximum capability. If your system runs continuously on the hottest days but keeps the house 20 to 25 degrees cooler than outside, it is working as designed. Close blinds on sun-facing windows, avoid using the oven, and limit opening exterior doors to reduce the cooling load during extreme heat.

Why Are Some Rooms Cold While Others Stay Hot?

Uneven temperatures room to room usually point to a distribution problem rather than an equipment problem. The AC system itself may be working perfectly, but the cooled air is not reaching all areas of the home equally.

Ductwork issues

Ductwork is the system of metal or flexible tubes that carry cooled air from the air handler to the supply registers (vents) in each room. Ductwork problems are the most common cause of uneven cooling. Disconnected duct sections, torn flexible duct, or poorly sealed joints allow cooled air to leak into the attic, crawl space, or wall cavities instead of reaching the intended room. A duct system with 20 to 30% leakage (which is common in homes over 15 years old that have never had ductwork sealed) means one-fifth to one-third of the cooled air you are paying to produce never reaches the living space. The rooms farthest from the air handler are affected most because they are at the end of the longest duct runs. A professional duct inspection with a duct blaster test (a device that pressurizes the duct system and measures total leakage) costs $150 to $400. Duct sealing to fix the leaks costs $500 to $2,000 depending on accessibility and extent of damage.

Undersized system

An AC system that is too small for the home's square footage and cooling load produces enough cooling for nearby rooms but cannot keep up with the total demand, leaving distant rooms warm. This often becomes apparent after a home addition, finishing a basement, or converting a garage to living space without upgrading the AC system. A Manual J load calculation (an engineering calculation that accounts for square footage, insulation values, window area and orientation, climate zone, and occupancy) determines the correct system size in tons. An undersized system runs constantly without ever satisfying the thermostat. The solution is either upgrading to a properly sized system or adding a supplemental mini-split (a ductless AC system with its own outdoor compressor and indoor air handler) to the underserved rooms. See our HVAC replacement cost guide for full system pricing.

Closed or blocked registers

Walk through every room and check every supply register (the vent where air blows out) and every return air grille (the larger vent where air is drawn back to the system). Registers that are closed, blocked by furniture, or covered by rugs restrict airflow to that room. Unlike what some homeowners believe, closing registers in unused rooms does not save energy. It increases duct pressure, reduces total system airflow, and can cause the evaporator coil to ice over. Open all registers to at least the halfway position and move furniture at least 6 inches away from supply and return vents.

Second-floor heat

In two-story homes, the upper floor is almost always warmer than the ground floor because hot air rises. A single-zone AC system (one thermostat controlling the entire house) cools the downstairs to the set temperature and shuts off while the upstairs remains 3 to 8 degrees warmer. Solutions include a zoning system (motorized dampers in the ductwork that direct more air upstairs when needed, costing $2,000 to $4,000 installed), setting the thermostat to a lower temperature and using a portable fan upstairs, or installing a supplemental ductless mini-split on the upper floor. Some homeowners partially close downstairs registers to redirect airflow upstairs, but this only works within a narrow range before it causes pressure problems.

Why Does Your AC Turn On and Off Every Few Minutes?

Short cycling means the AC compressor starts, runs for 2 to 10 minutes, shuts off, then restarts a few minutes later. A normal cooling cycle lasts 15 to 20 minutes or longer. Short cycling prevents the system from running long enough to adequately cool the house and puts severe stress on the compressor because each startup draws 4 to 8 times the normal running amperage. Over time, short cycling burns out the compressor, which is the most expensive component in the system.

Electrical causes

A failing capacitor may not provide enough starting power for the compressor to run consistently. The compressor starts, struggles, and the thermal overload protection switch (a safety device built into the compressor that shuts it down when it overheats) trips after a few minutes. The compressor cools down, the overload resets, and the cycle repeats. A failing contactor with pitted or burned contacts may make intermittent electrical connection, causing the compressor to drop out randomly. Both are relatively inexpensive repairs: $150 to $350 for a capacitor, $150 to $375 for a contactor.

Oversized system

An AC system that is too large for the home (too many tons of cooling capacity for the square footage and cooling load) cools the air around the thermostat very quickly, satisfying the thermostat set point in 5 to 10 minutes. The system shuts off, the temperature rises within a few minutes as heat from the walls, attic, and windows radiates back into the room, and the system starts again. This rapid cycling is inherent to an oversized system and cannot be fixed without replacing the system with a correctly sized one. If short cycling started when the system was new and has always been present, oversizing is the likely cause. Use our HVAC cost calculator to estimate proper sizing and replacement cost.

Other causes of short cycling

Low refrigerant causes the low-pressure safety switch to shut the compressor down before it can complete a cooling cycle. A dirty air filter causes high head pressure that triggers the high-pressure safety switch. A dirty condenser coil reduces heat rejection and causes the same high-pressure cutout. A thermostat located in a drafty area, near a supply vent, or in direct sunlight reads incorrect temperatures and cycles the system erratically. If short cycling started recently, check the filter and condenser coil first, then call a technician to check refrigerant charge and electrical components.

Which DIY Fixes Actually Work and Which Make Things Worse?

When your AC stops cooling, the urge to fix it yourself is understandable, especially on a hot day. Some DIY actions genuinely help. Others cause additional damage, increase the eventual repair cost, or create safety hazards.

DIY fixes that work

Replacing the air filter is the single most effective DIY action. It resolves approximately 25 to 30% of "AC not cooling" calls on its own and costs under $25. Checking and correcting thermostat settings resolves another 15 to 20% of calls. Resetting a tripped breaker is straightforward and safe as long as you only do it once (if the breaker trips again, stop). Clearing debris from around the outdoor unit and gently rinsing the condenser coil with a garden hose are safe, effective maintenance steps that can restore lost cooling capacity. Opening closed or blocked registers throughout the house addresses uneven cooling. Pouring a cup of white vinegar down the condensate drain access port clears minor clogs and prevents water backup.

DIY fixes that cause damage

Do not pour water on the outdoor unit to "cool it down." While a gentle hose rinse on the coil is fine, dumping buckets of water on a running system, especially on the electrical components, can cause short circuits and component damage. Do not add refrigerant yourself, even if you find a can of refrigerant at a store. Besides being illegal without EPA certification, incorrect refrigerant charge (too much or too little) damages the compressor, and you have no way to measure the correct charge without professional gauges. Do not straighten bent condenser fins with a screwdriver or knife. Use a proper fin comb (available at hardware stores for $10 to $15) or leave it for a professional. Damaged fins restrict airflow. Do not attempt to jump-start the compressor by bridging electrical contacts. Capacitors store lethal amounts of electrical charge even when the power is off. Touching the wrong terminal can cause a severe electrical shock. Do not remove the access panels on the outdoor unit while it is running. Moving parts and high-voltage connections inside the unit are dangerous.

Temporary cooling measures while waiting for repair

If the AC cannot be fixed immediately and you need to manage indoor temperature, close all curtains and blinds, especially on south-facing and west-facing windows. Avoid using the oven, stove, or dishwasher (all generate significant heat). Use portable fans or ceiling fans to circulate air. Set the thermostat fan to ON to circulate air even though the compressor is not cooling it, as moving air feels 3 to 4 degrees cooler than still air on the skin. Open windows at night if the outdoor temperature drops below the indoor temperature. Spend the hottest hours (2 PM to 7 PM) at a library, mall, or other air-conditioned public space if the house becomes uncomfortably hot.

When Should You Shut Your AC Off Immediately?

Most AC problems are not emergencies and the system can continue running while you schedule a repair. However, certain symptoms indicate a situation where continued operation will cause significant additional damage or pose a safety risk. Turn the system off at the thermostat and call a technician if any of the following are present.

Ice forming on the system

Ice on the refrigerant lines, the evaporator coil, or the outdoor unit means the system is operating outside its design parameters. Continued operation allows the ice to build until the compressor is trying to pump liquid refrigerant instead of gas (a condition called liquid slugging), which can destroy the compressor valves. Turn the system off, set the fan to ON, and allow the ice to thaw completely before calling for service. See the frozen coil section above for the complete thaw procedure.

Burning or electrical smell

A burning smell from the vents or from the outdoor unit indicates an overheating motor, melting wire insulation, or a failing electrical component. Turn the system off immediately at the thermostat. If the smell is strong or you see smoke, turn the system off at the breaker panel and call a technician for emergency service. Do not turn the system back on until a technician has inspected it. An electrical component operating at temperatures high enough to produce a burning smell is a fire hazard. For emergency repair pricing, see our emergency HVAC repair guide.

Water leaking from the indoor unit

Water pooling around the air handler or dripping from the ceiling (if the air handler is in the attic) indicates a clogged condensate drain or a cracked drain pan. While not immediately dangerous to the equipment, continued operation produces more condensate that has nowhere to drain, causing water damage to walls, ceilings, insulation, and flooring. Turn the system off and address the drain clog before restarting.

Breaker tripping repeatedly

If the outdoor unit breaker trips, you can reset it once. If it trips again, leave it off. A breaker trips because the circuit is drawing more current than its rated capacity, which means something in the electrical system is faulty. Repeatedly resetting a tripping breaker can overheat the wiring inside the walls and create a fire hazard. A technician needs to identify whether the issue is a shorted component, a grounded compressor, or a wiring fault before the system can safely operate.

Loud banging or grinding noises

A loud banging noise from the outdoor unit suggests a broken internal component, potentially a connecting rod or piston inside the compressor, or a loose fan blade striking the housing. A grinding noise indicates metal-on-metal contact from failed bearings. Both conditions cause progressively worse damage with continued operation. Turn the system off and schedule service.

When Should You Call a Professional?

After working through the DIY checks described above, call a professional HVAC technician if any of the following apply.

Nothing on the DIY checklist resolved the problem

If you have replaced the filter, verified the thermostat settings, confirmed the outdoor unit has power and the fan is spinning, cleared debris from around the unit, opened all registers, and the system still is not cooling, the remaining possible causes (refrigerant leak, compressor failure, electrical component failure, control board malfunction) all require professional diagnostic tools and expertise to identify and repair. A technician arrives with refrigerant gauges, an electrical multimeter, a clamp-on ammeter, and an electronic leak detector. These instruments provide specific readings that isolate the failed component.

The system will not turn on at all

If neither the indoor blower nor the outdoor unit runs when the thermostat calls for cooling, and you have verified the breakers are on and the thermostat is set correctly, the issue may be a failed control board, a broken thermostat wire, a blown transformer (a small device that converts 240-volt power to the 24 volts that operates the thermostat circuit), or a failed thermostat. A technician traces the electrical circuit from the thermostat through the control board to identify where the signal is lost.

You suspect a refrigerant leak

If ice keeps forming on the system even with a clean filter and all vents open, or if the system blows slightly cool but not cold air and runs continuously, the system is likely low on refrigerant. Only an EPA-certified technician can legally handle refrigerant, locate the leak, repair it, and recharge the system. Refrigerant leak repair costs $200 to $1,500 depending on the leak location, plus $200 to $700 for the refrigerant recharge. See our refrigerant recharge guide for the full cost breakdown.

The system is 12 or more years old

AC systems older than 12 years are in the zone where component failures accelerate and repair costs accumulate. If your system is in this age range and stops cooling, have the technician provide both a repair quote and an honest assessment of the system's remaining useful life. A $400 repair on a 14-year-old system may buy you another year before the next component fails, making replacement the more cost-effective path. Our when to replace your HVAC guide walks through the complete repair-versus-replace decision. Use our HVAC cost calculator to estimate what a replacement system would cost for your home.

How Long Is It Safe to Stay in a Hot House?

When the AC fails in warm weather, indoor temperatures can climb rapidly, especially in well-insulated homes with south or west-facing windows. Understanding heat safety thresholds helps you make informed decisions about when to tolerate the heat, when to take temporary cooling measures, and when to leave the home.

Temperature thresholds and risk levels

At indoor temperatures of 80 to 85 degrees, most healthy adults are uncomfortable but not at medical risk. This is the range where fans, cold water, and reduced activity are adequate coping measures. At 85 to 90 degrees indoors, the risk of heat exhaustion increases, particularly with physical activity. At 90 to 95 degrees, heat exhaustion can develop within 2 to 4 hours even at rest, and the risk is significantly higher for vulnerable individuals. Above 95 degrees indoors, heat stroke (a life-threatening medical emergency where the body loses its ability to regulate temperature) becomes a real possibility for everyone, and vulnerable individuals are at serious risk within 1 to 2 hours.

Who is most vulnerable

Elderly adults (especially those over 75), infants and children under 4, pregnant women, people with heart disease, respiratory conditions, diabetes, or kidney disease, and anyone taking medications that affect sweating or temperature regulation (including diuretics, beta-blockers, and some psychiatric medications) are at elevated risk. Pets are also vulnerable. Dogs and cats cannot sweat and rely on panting, which becomes ineffective when the ambient air temperature exceeds their body temperature. If your household includes anyone in these categories and the indoor temperature exceeds 85 degrees with no prospect of repair within a few hours, relocate to a cooled environment.

Heat exhaustion symptoms

Watch for heavy sweating, cold and clammy skin, fast and weak pulse, nausea or vomiting, muscle cramps, tiredness, weakness, dizziness, headache, and fainting. If someone displays these symptoms, move them to a cooler environment, apply cool wet cloths, and have them sip water slowly. If symptoms worsen or last more than an hour, seek medical attention.

Heat stroke warning signs

Heat stroke is a medical emergency. Symptoms include a body temperature of 103 degrees or higher, hot and red and dry skin with no sweating, a rapid and strong pulse, headache, dizziness, nausea, confusion, and loss of consciousness. Call 911 immediately. Move the person to a cooler environment. Cool them with whatever is available (cool cloths, cool bath, fan). Do not give fluids if they are unconscious or confused.

Protecting your home while the AC is off

While waiting for repair, minimize heat gain by closing all curtains and blinds (especially on south and west windows), closing doors to unused rooms to concentrate cooling efforts in occupied spaces, turning off unnecessary lights and electronics (all produce heat), avoiding the oven and stove (use a microwave or eat cold food), and running exhaust fans in bathrooms and the kitchen to vent warm air. If outdoor temperatures drop below indoor temperatures after sunset, open windows on opposite sides of the house to create cross-ventilation.

How Much Does It Cost to Fix an AC That Is Not Cooling?

The cost to restore cooling depends entirely on the cause. Here is what each common repair costs, from the simplest and least expensive to the most complex and costly.

The service call fee ($75 to $150) covers the technician's travel and diagnostic time. Some companies apply this fee toward the cost of the repair if you authorize the work. Others charge it separately. Ask about the diagnostic fee structure when you schedule the appointment. For a comprehensive overview of all AC repair costs, see our complete AC repair cost guide.

When repair cost approaches replacement cost

If the repair estimate exceeds $1,200, get a second opinion and also request a quote for a full system replacement. A new central AC system costs $3,500 to $7,500 installed depending on size, efficiency, and brand. For systems over 10 years old, a repair costing $1,000 or more is often better applied toward a new system that comes with a full manufacturer warranty and significantly higher energy efficiency. Our HVAC replacement cost guide breaks down the full pricing for new system installation.

How to reduce the repair cost

Schedule non-emergency repairs during the off-season (fall and spring) when technicians have more availability and some companies reduce pricing. Ask whether the diagnostic fee is applied toward the repair cost. For repairs over $500, get at least two quotes. Ask whether the failed part is still under the manufacturer's warranty (most parts carry a 5 to 10 year warranty, and the compressor often carries a 10 year warranty). If the part is under warranty, you pay only the labor cost, which can reduce the total by 30 to 60%.

Frequently Asked Questions