Air Conditioner Not Cooling: Causes and Fixes

An air conditioner that is not cooling has a symptom, not a single diagnosis. Start with the thermostat, filter, airflow, power, outdoor-unit clearance, ice, and condensate. Those checks can identify a simple maintenance problem, but refrigerant, compressor, high-voltage electrical, concealed-coil, and ductwork issues require a qualified HVAC professional.

This guide covers U.S. residential central split systems, heat pumps in cooling mode, ductless mini-splits, window air conditioners, and portable air conditioners. Automobile air conditioning is different and is not covered here; vehicle refrigerant service follows EPA Section 609 rather than the stationary-equipment rules discussed below.

A typical split-system air conditioner moves heat from indoors to outdoors. The indoor evaporator coil absorbs heat and humidity, while the outdoor condenser coil releases that heat. If either airflow or heat transfer is restricted, the system may run constantly, blow warm air, freeze, shut down, or fail to start.

For manufacturer troubleshooting sequences that begin with settings, filters, airflow, power, outdoor-unit condition, and visible ice, see Carrier’s AC troubleshooting guide and Trane’s troubleshooting guidance.

First, identify what “not cooling” means

The fastest way to avoid the wrong fix is to classify the symptom before touching anything. Use this table as a starting point—not as a substitute for professional testing.

What you observe	Useful initial branches
No air from the vents	Thermostat, indoor power, blower, filter, condensate float switch, or control failure
Weak airflow	Dirty filter, blocked return, closed registers, frozen coil, dirty blower or coil, or duct restriction
Normal airflow but warm air	Wrong thermostat setting, outdoor unit not operating, dirty condenser, refrigerant or compressor problem, or duct leakage
Runs but never reaches the setpoint	Low or incorrect charge, dirty coil, duct leakage, undersizing, poor insulation, excessive solar gain, or unusually high outdoor temperature
Outdoor unit is silent	Breaker or disconnect, thermostat signal, contactor, capacitor, control board, wiring, or safety switch
Outdoor fan runs but the air is warm	Compressor, refrigerant, condenser-coil, or control problem; the fan running does not prove the compressor is working
Ice on the refrigerant line or coil	Restricted airflow, dirty coil, low refrigerant, blower problem, or operation below the equipment’s permitted outdoor temperature
Water indoors	Clogged condensate drain, thawing frozen coil, damaged pan, failed condensate pump, or float-switch problem
One room is hot	Closed register, blocked return, duct leak or disconnection, balancing problem, solar gain, insulation, or zoning issue
Rapid on-and-off cycling	Oversizing, thermostat or control problem, airflow restriction, low charge, electrical fault, or safety control
Window AC cools its discharge air but not the room	Incorrect capacity, poor window seal, open window or door, blocked outdoor coil, or inadequate room enclosure
Portable AC runs but barely cools	Exhaust-hose leakage or blockage, intake restriction, full condensate reservoir, poor room sealing, or a room larger than the unit’s rating

Safe homeowner checks, in the right order

1. Verify the thermostat

1. Set the mode to Cool, not Heat, Off, or Fan-only.
2. Set the temperature below the current room temperature.
3. Set the fan to Auto while diagnosing. A fan set to On can circulate unconditioned air between cooling cycles and make the supply air feel warm.
4. Check whether a schedule, vacation mode, or temporary hold is overriding the temperature you selected.
5. Replace batteries if the thermostat uses them and its screen is blank or dim.
6. Make sure the thermostat is not in direct sunlight, beside a lamp, above a supply register, or near another heat source.

Thermostat labels and menus differ by manufacturer. If the display or wiring configuration is unfamiliar, use the equipment manual rather than guessing.

2. Inspect or replace the air filter

Turn the system off before removing the filter. Confirm that:

• The filter is the correct size and type.
• The airflow arrow points toward the furnace or air handler.
• A disposable filter is replaced rather than washed.
• A reusable filter is cleaned only as its instructions specify and is completely dry before installation.
• The filter is not unusually thick or restrictive for the equipment.

A higher-rated or thicker filter is not automatically better if the system was not designed to move air through it. A restricted filter can reduce airflow, encourage coil icing, increase runtime, and contribute to equipment damage.

ENERGY STAR recommends inspecting, cleaning, or changing central-AC, furnace, and heat-pump filters monthly. Actual replacement frequency depends on the filter, pets, dust, construction activity, occupancy, and the manufacturer’s instructions.

3. Check registers, returns, and visible ducts

Walk through the home and check several locations:

• Open supply registers and remove furniture, rugs, curtains, and other obstructions.
• Keep return grilles open and unobstructed. A blocked return can starve the blower of air even when the filter is clean.
• Look for flexible duct that is crushed, sharply kinked, disconnected, or visibly collapsed.
• Check whether air is weak at every register or only at certain rooms.
• Do not close numerous registers to force more air into another room; that can increase system pressure and worsen airflow.

Airflow problems can reduce efficiency by up to 15%, according to an ENERGY STAR maintenance estimate; the actual effect varies by system and home. If the filter is clean but airflow remains weak, possible causes include a dirty evaporator coil, dirty blower wheel, failing blower motor, closed damper, duct restriction, or static-pressure problem.

4. Check power without opening equipment

For a central system, a homeowner can visually check the electrical panel for a clearly tripped HVAC breaker, the indoor service switch, and the outdoor disconnect near the condenser. Do not remove electrical covers, test a capacitor, bypass a safety switch, or touch wiring.

If you are comfortable doing so, reset a tripped breaker once. If it trips again—especially immediately—leave it off and call a qualified technician. Repeated resets can turn an electrical or compressor fault into a larger failure. Capacitors can retain a dangerous charge even after power is removed.

A blank thermostat may be caused by depleted batteries, loss of indoor-unit power, a blown low-voltage fuse, a condensate float switch, transformer failure, or control trouble. A homeowner cannot reliably distinguish those causes by looking at the thermostat alone.

5. Inspect the outdoor condenser safely

Turn the system off before clearing debris or cleaning around the outdoor unit. You may:

• Remove leaves, grass clippings, plastic, and other loose debris.
• Trim vegetation that blocks the coil or the fan’s discharge.
• Check whether the outdoor fan operates when the thermostat calls for cooling.
• Gently rinse accessible coil surfaces with a garden hose if the owner’s manual permits it.

Do not use a pressure washer, open the electrical compartment, straighten severely damaged fins without the proper tool, or work inside the unit. If the outdoor fan runs but the home still receives warm air, the compressor may not be operating, the charge may be wrong, the condenser may be dirty, or a control problem may be present.

The outdoor coil must reject the heat removed from the home. Dirt and vegetation can reduce cooling performance and increase runtime; ENERGY STAR includes outdoor-coil and debris removal in its maintenance guidance.

6. Look for ice before running the system again

Check the larger insulated refrigerant line, the visible indoor coil or air-handler cabinet, and the outdoor tubing. Frost or ice can indicate:

• A dirty or overly restrictive filter
• Blocked return or supply airflow
• A dirty evaporator coil or blower wheel
• A failing blower motor
• Low or incorrect refrigerant charge
• Operation in outdoor conditions unsuitable for that equipment

If ice is present:

1. Set cooling to Off.
2. Leave the system off and allow the ice to thaw naturally.
3. Protect floors, ceilings, and electronics from meltwater.
4. Replace a dirty filter and restore obvious airflow restrictions.
5. Do not chip at the ice.
6. Do not use a torch, space heater, or hair dryer to accelerate thawing.
7. Arrange service if the ice returns or the cause is not obvious.

Repeatedly thawing and restarting a frozen system does not fix the underlying fault. Carrier’s frozen-AC guidance warns that continued operation can damage the system.

7. Check for condensate and water damage

During cooling, an air conditioner normally produces condensation. Water should drain through the designated condensate line or pan—not overflow into a ceiling, wall, floor, or electrical compartment.

Turn the system off and arrange service if you see:

• Water around the indoor air handler
• An overflowing or full drain pan
• Ceiling stains below an attic unit
• Musty odors or persistently high indoor humidity
• An emergency drain line dripping continuously
• A condensate pump that does not operate
• The AC shutting off when the thermostat calls for cooling

A clogged drain may activate a float switch that intentionally shuts down the cooling system to limit water damage. Hidden attic drains, condensate pumps, inaccessible pans, and water near wiring are technician territory. Do not pour bleach, vinegar, compressed air, or chemical drain cleaner into an unfamiliar drain configuration; systems differ, and an incorrect treatment can damage parts or push debris farther into the system.

ENERGY STAR warns that plugged condensate drains can cause water damage and affect humidity. EPA also recommends keeping drip pans clean and condensate lines unobstructed because standing moisture can contribute to mold problems; see the EPA moisture and mold guide.

When the AC is not turning on

“The AC will not start” is different from “the AC runs but does not cool.” Work through these non-invasive checks:

• Is the thermostat screen on and set to Cool?
• Are the batteries good, if applicable?
• Is the indoor service switch on?
• Is the HVAC breaker tripped?
• Is the outdoor disconnect visibly in its normal position?
• Is there water in the indoor pan that could have activated a float switch?

If the indoor blower does not run, suspect indoor power, the thermostat signal, a float switch, blower motor, control board, or low-voltage problem. If the indoor blower runs but the outdoor unit is silent, suspect the outdoor power supply, thermostat signal, contactor, capacitor, control board, wiring, or compressor controls.

Do not remove panels or attempt to replace electrical components. If a breaker trips a second time, leave it off. Carrier’s troubleshooting instructions also recommend escalating a recurring electrical trip rather than repeatedly resetting it.

When the AC runs but blows warm air

Normal airflow with warm supply air commonly points beyond the filter, but it does not prove a refrigerant problem. Check that the thermostat is in Cool and the outdoor unit operates. Then consider:

• The outdoor condenser is not receiving power.
• The outdoor fan runs but the compressor does not.
• The condenser coil is blocked or dirty.
• The evaporator coil is frozen.
• The refrigerant charge is low or incorrect.
• The compressor, capacitor, contactor, or control has failed.
• Conditioned air is escaping through disconnected or leaking ducts.

A fan set to On can also make the air feel warm between cooling cycles, but it does not explain every warm-air complaint. If the outdoor unit hums, struggles to start, makes loud electrical buzzing, or repeatedly stops, turn the system off and call for service.

Common causes, what you can do, and when to stop

Possible cause	Typical signs	Homeowner action	Professional work
Thermostat setting or battery	System appears inactive or fan behavior is confusing	Verify Cool, setpoint, schedule, fan Auto, and batteries	Thermostat, wiring, or control diagnosis
Dirty or restrictive filter	Weak airflow, long runtime, icing	Replace or clean according to instructions	Airflow and static-pressure testing if symptoms remain
Blocked return or supply	Weak air at several or selected registers	Open registers and clear obstructions	Blower, coil, damper, or duct diagnosis
Dirty outdoor coil	Long runtime, weak cooling, high outdoor-unit heat	Clear debris and gently rinse if permitted	Deep cleaning, fin, fan, and electrical inspection
Frozen evaporator coil	Ice, weak airflow, water after thawing	Turn cooling off and thaw naturally	Determine whether airflow, blower, coil, temperature, or charge caused freezing
Low or incorrect refrigerant charge	Gradual loss of cooling, long runtime, possible ice or humidity	Do not connect gauges or add refrigerant	Verify charge, locate and repair leaks, evacuate and charge to specification
Condensate blockage	Indoor water, pan overflow, musty odor, shutdown	Turn off system and protect the area	Clear hidden drain, inspect pan, pump, and float switch
Electrical or compressor failure	Breaker trips, outdoor unit hums, fan-only operation	Check power visually; reset a breaker only once	Electrical measurements and component replacement
Duct leakage or disconnection	Hot rooms, weak distant registers, attic or crawlspace losses	Inspect only accessible ducts	Leakage, static-pressure, balancing, sealing, and insulation work
Incorrect equipment size or building heat gain	Continuous operation, short cycling, poor humidity control	Use temporary shading and close openings	Load calculation, envelope, duct, and equipment assessment

Refrigerant: why “just recharge it” is incomplete

In a properly sealed air-conditioning system, refrigerant circulates in a closed loop; it is not consumed like fuel. A low charge may result from a leak, an installation or charging error, prior service, component damage, or an improperly commissioned system.

Possible clues include gradually declining cooling, long runtimes, warm supply air, ice on tubing or coils, and higher humidity. Those clues are not conclusive. A technician must verify airflow, operating conditions, the charge, and the refrigerant circuit before identifying the cause.

If a technician recommends a “recharge,” ask:

• Where is the leak, if a leak is suspected?
• How was it located?
• Will it be repaired, or is the system only being topped off?
• Will the system be evacuated and charged according to the equipment manufacturer’s specification?
• What refrigerant is listed on the nameplate?
• Is the proposed refrigerant approved and compatible with this equipment?
• Would repair be sensible given the system’s age, condition, and future parts or refrigerant availability?

EPA advises homeowners to ask technicians to locate and repair leaks instead of simply topping off a leaking system. Adding or removing refrigerant, or opening a covered stationary-equipment refrigerant circuit, requires the appropriate EPA Section 608 technician certification.

Never mix refrigerants or use an unapproved substitute because it is cheaper or easier to obtain. Do not add R-22, R-410A, R-32, R-454B, propane-based “22a,” or another refrigerant unless the equipment and applicable rules specifically support it. EPA has warned that flammable propane-based substitutes used in equipment not designed for them can create fire and explosion hazards.

U.S. refrigerant-transition context for repair or replacement

This issue should not determine the first 10 minutes of troubleshooting, but it matters when an older system needs major repair or replacement. EPA rules distinguish between repairing an existing system and manufacturing, importing, or installing new equipment.

As of August 10, 2026, EPA guidance states that a new residential split system installed after January 1, 2026, generally must use refrigerant with a global warming potential below 700. Existing systems may continue to be repaired and used, and EPA’s May 26, 2026 final rule allows certain pre-January 1, 2025 inventory using higher-GWP refrigerants to continue being installed. Exact requirements depend on equipment type, manufacture or import date, system configuration, and the applicable rule.

That does not mean every R-410A or R-22 system must be replaced immediately. Before publishing or acting on a replacement proposal, check the latest EPA HFC phasedown FAQ, the EPA Technology Transitions Program, and the applicable sector restrictions.

Why a clean filter may not solve weak airflow

A clean filter rules out only one possible restriction. Continued weak airflow may come from:

• A blocked or undersized return grille
• A collapsed, disconnected, or poorly routed duct
• A dirty evaporator coil
• A dirty blower wheel
• An overly restrictive filter or filter cabinet
• A failing blower motor or control
• Closed dampers or balancing problems
• Excessive static pressure

Indoor evaporator coils and blower assemblies are often inside an air handler or furnace cabinet. Do not spray household cleaner, bleach, or water into a concealed coil or open an electrical compartment. A technician can inspect the coil, measure airflow and static pressure, and determine whether cleaning or repair is appropriate.

Ducts, insulation, and construction-related causes

If the equipment appears to cool but one or more rooms remain hot, the problem may be in the distribution system or the building envelope. Look for accessible signs of:

• Disconnected or leaking supply ducts in an attic, crawlspace, basement, or garage
• Uninsulated or poorly insulated ducts in hot spaces
• Inadequate return air
• Air leakage around doors, windows, penetrations, or attic hatches
• Insufficient insulation
• Strong solar gain through unshaded windows
• Incorrect zoning or closed dampers

ENERGY STAR estimates that a typical forced-air home may lose 20–30% of duct air through leaks, holes, and poorly connected ducts; actual losses vary significantly. Accessible duct joints should be sealed with mastic or approved metal-backed tape, not ordinary cloth “duct tape.” Inaccessible or extensive duct repairs should be professionally assessed.

Useful professional tests may include airflow measurement, static-pressure testing, duct-leakage testing, return-air assessment, and inspection in attics, crawlspaces, garages, and basements.

Running constantly, short cycling, and poor humidity control

When continuous operation is a problem

An AC may run for long periods during extreme heat and still be operating normally. Continuous operation becomes more concerning when the home never approaches the setpoint, indoor humidity remains high, airflow is weak, ice appears, or the behavior is a change from normal.

Possible causes include low or incorrect refrigerant charge, dirty coils, duct leakage, poor insulation, excessive air leakage, equipment failure, or an undersized system. Correcting the building envelope or ductwork may be more effective than replacing the compressor.

When the system cycles too quickly

Short cycling can result from an oversized system, thermostat or control trouble, airflow restriction, low charge, or an electrical or safety fault. A larger replacement is not automatically the answer. An oversized system may reach the thermostat quickly without removing enough humidity, and frequent starts can add wear.

DOE Building America recommends recognized load calculations for equipment selection, and ACCA Manual J is the ANSI-recognized residential load-calculation standard. Ask for a load calculation rather than accepting a replacement size based only on square footage. See also DOE’s HVAC proper-sizing guidance.

Central AC, heat pumps, and ductless mini-splits

Central split-system AC

A central system has an indoor blower and evaporator coil, an outdoor condenser and compressor, refrigerant lines, ducts, and a condensate system. The checks above apply, but indoor-coil, blower, drain, and duct issues may be concealed inside the equipment or building.

Heat pump in cooling mode

A heat pump cools much like an air conditioner but also has a reversing valve and additional controls. In summer, troubleshoot thermostat configuration, filters, airflow, outdoor-unit operation, ice, condensate, and visible obstructions as you would for central AC. A reversing-valve, communication, or control fault can also prevent proper cooling.

In winter heating mode, a brief change in supply-air temperature during a defrost cycle can be normal. Persistent cold air, heavy ice, or failure to recover requires service. Do not apply furnace expectations to heat pumps; heating supply air may feel less hot than furnace air. Carrier’s heat-pump guidance explains these different operating behaviors.

Ductless mini-split

For a mini-split, check the remote or controller mode and setpoint, clean the indoor head’s filters, make sure the indoor head and outdoor unit have power, and clear obstructions around the outdoor unit. There is no conventional central duct system, so weak cooling from one head may involve that head’s filter, airflow, sensor, louvers, condensate, communication, or refrigerant connection. Do not open the refrigerant lines or outdoor electrical compartment.

Window air conditioner not cooling

Room units have different failure modes from central systems. Check:

• Cooling mode rather than fan-only or an energy-saver setting that is temporarily inactive
• A clean front filter
• Unobstructed air intake and discharge
• Side curtains and the window opening sealed
• Closed doors and windows in the room
• The ventilation lever or fresh-air damper closed if it is admitting unwanted outdoor air
• Correct installation, support, and tilt according to the manual
• An unobstructed outdoor coil
• Capacity appropriate for the room

A window unit can produce cold discharge air yet fail to cool the room if hot outdoor air enters around the window, the room is too large, sunlight and internal heat loads are substantial, or the outdoor coil cannot reject heat. Use the manufacturer’s room-AC troubleshooting guidance for model-specific behavior.

Window-AC capacity starting points

The following ENERGY STAR examples assume an approximately 8-foot ceiling. They are starting points, not a replacement for the manufacturer’s sizing guidance or a full assessment of the room.

Room area	Nominal capacity
100–150 sq. ft.	5,000 Btu/h
150–250 sq. ft.	6,000 Btu/h
250–300 sq. ft.	7,000 Btu/h
300–350 sq. ft.	8,000 Btu/h
350–400 sq. ft.	9,000 Btu/h
400–450 sq. ft.	10,000 Btu/h
450–550 sq. ft.	12,000 Btu/h
550–700 sq. ft.	14,000 Btu/h

High ceilings, intense sun, poor insulation, kitchens, occupancy, and open-plan layouts can change the required capacity. Oversizing can reduce dehumidification and increase cycling. See ENERGY STAR’s room-AC sizing information.

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Portable air conditioner not cooling

A portable unit may blow cold air at its outlet while adding too much heat to the room through a poor exhaust installation. Check:

• The exhaust hose is attached securely and is not kinked, crushed, leaking, or extended beyond the manual’s limit.
• The window panel and hose opening are sealed.
• Intake filters and intake openings are clean and unobstructed.
• The room’s doors and windows are closed.
• The condensate tank or tray is not full.
• The unit is not pressed against a wall or furniture.
• The room is within the manufacturer’s rated area.
• The unit is in Cool mode with the correct setpoint.

Possible causes include a blocked filter, disconnected or blocked exhaust hose, full water tray, open windows or doors, heat-producing appliances, room size, or low refrigerant. Midea’s portable-AC manual lists these model-specific troubleshooting branches.

Room units can also ice when airflow is restricted or when cooling operates below the permitted outdoor-temperature range. One Frigidaire guide identifies temperatures below 60°F as a possible icing condition for certain room units; that is model-specific, not a universal threshold. Follow the manual for your unit.

Temperature measurements: useful clue, not a pass/fail test

Homeowners often hear that a correctly operating AC must have a 15–20°F difference between return and supply air. That number is common industry shorthand, but it is not universal. The result varies with indoor temperature and humidity, outdoor conditions, airflow, equipment design, load, and operating state.

ACCA cautions against treating the 15–20°F rule as a one-size-fits-all diagnostic standard. Do not add refrigerant solely because a measurement falls outside that range, and do not declare a system healthy solely because it falls inside it.

If you want to record a clue for a technician:

1. Use a reliable thermometer.
2. Measure return air near the air handler or main return.
3. Measure supply air at a nearby register.
4. Wait until the system has operated steadily rather than measuring immediately after startup.
5. Record the indoor temperature, outdoor temperature, humidity if available, thermostat setting, and whether airflow seems weak.

Professional diagnosis requires verified airflow and comparison with the manufacturer’s performance data.

When to call an HVAC technician immediately

• Ice returns after the system has thawed.
• A breaker trips again after one reset.
• You smell burning insulation, see smoke or melted wiring, or hear loud electrical buzzing.
• Water is accumulating near electrical equipment or damaging a ceiling.
• The outdoor unit hums but does not start.
• The compressor, capacitor, contactor, blower motor, or control board is suspected.
• Refrigerant is suspected or the system needs a charge.
• The evaporator coil or drain is concealed or inaccessible.
• The unit is in an attic, crawlspace, or other hazardous location.
• Basic setting, filter, airflow, power, and debris checks do not restore cooling.
• The system is under warranty or a recent installation has never cooled properly.

A qualified technician should be able to evaluate more than supply-air temperature. A proper diagnosis may include:

• Airflow and static-pressure measurements
• Filter, blower, evaporator-coil, and condenser-coil inspection
• Electrical measurements and safety-control checks
• Refrigerant charge verification under the correct operating conditions
• Leak detection and repair when needed
• Condensate pan, drain, pump, and float-switch inspection
• Duct leakage, return-air, and distribution assessment
• Equipment match, installation, and sizing review

Repair versus replacement

Do not choose replacement solely because the unit is old or because it is running frequently. Ask:

• How old is the system, and has the problem recurred?
• Is this an isolated repair or evidence that multiple major components are deteriorating?
• Are the indoor and outdoor units properly matched?
• Are ducts, insulation, air leakage, or solar gain causing the comfort complaint?
• Is the refrigerant obsolete, expensive, or difficult to obtain?
• Would the repair correct the underlying problem or only restore operation temporarily?
• Does the replacement proposal include a load calculation rather than a square-footage guess?
• What changes are needed to the electrical service, drain, ducts, refrigerant lines, or controls?
• What warranties cover parts, labor, and refrigerant?

EPA recommends professional evaluation when equipment is more than 10 years old or is not keeping the home comfortable. That is a reason to evaluate the system—not an automatic replacement command. A well-sized, properly installed repair may be sensible, while a newer system with chronic duct or sizing problems may need a broader correction.

What information to give the technician

Instead of saying only “the AC is not cold,” record:

• Equipment type: central AC, heat pump, mini-split, window, or portable
• Whether there is no airflow, weak airflow, or normal airflow
• Whether the outdoor fan and compressor appear to operate
• Thermostat mode, setpoint, and indoor temperature
• When the problem began and whether it is intermittent
• Whether ice, water, unusual odors, noises, or breaker trips occurred
• Whether a filter was recently changed or construction created extra dust
• Any recent electrical, duct, thermostat, refrigerant, or remodeling work
• Any previous refrigerant additions and the refrigerant listed on the nameplate

These observations help separate an airflow, electrical, refrigerant, condensate, distribution, and capacity complaint before the technician begins testing.

Prevention checklist

• Inspect the filter monthly and replace or clean it as directed.
• Keep supply registers and return grilles clear.
• Keep leaves, grass, and vegetation away from the outdoor condenser.
• Schedule a pre-season inspection, preferably in spring, before heavy cooling demand.
• Check accessible condensate outlets and respond promptly to indoor water.
• Seal accessible duct joints with mastic or approved metal-backed tape.
• Address attic insulation, duct insulation, air leakage, and excessive solar gain when rooms remain hot.
• Keep records of repairs, refrigerant additions, filters, and recurring symptoms.
• Have replacement equipment selected using a load calculation and matched-system requirements.

ENERGY STAR recommends annual pre-season checkups and monthly filter inspection.

Frequently Asked Questions

Why is my AC running but not cooling?

Common possibilities include a dirty filter or coil, blocked airflow, a frozen evaporator coil, a condenser that is not operating, a dirty outdoor coil, low or incorrect refrigerant charge, compressor trouble, duct leakage, or equipment that cannot meet the building’s heat load. Check the thermostat, filter, registers, returns, outdoor-unit clearance, ice, and power first. If cooling remains weak, arrange professional diagnosis rather than assuming it needs refrigerant.

Should I turn off an AC that is not cooling?

Turn it off if it is frozen, repeatedly trips a breaker, leaks water indoors, smells electrically burnt, makes abnormal electrical noises, or has water near electrical equipment. A system that simply runs during extreme heat may not need to be shut off immediately, but if basic checks do not restore cooling, schedule service.

Can a dirty filter cause an AC coil to freeze?

Yes. A restricted filter can reduce airflow over the evaporator coil and contribute to icing. However, ice can also result from a dirty coil, blower problem, low refrigerant, or unsuitable outdoor conditions. Turn cooling off, let the ice thaw naturally, replace the filter if needed, and call for service if freezing returns.

Does low refrigerant always mean there is a leak?

No. Low charge can result from a leak, incorrect installation or charging, prior service, or component damage. A properly sealed system does not normally consume refrigerant. Ask the technician to verify the charge and locate and repair a leak rather than repeatedly topping off the system.

How long does a frozen AC coil take to thaw?

Thawing time varies with the amount of ice, airflow, indoor temperature, and equipment. Leave cooling off and allow the ice to melt naturally; do not chip it or apply a torch, space heater, or hair dryer. Protect nearby floors and ceilings from meltwater. If the coil does not thaw or freezes again, call a technician.

Can I clean the outdoor condenser coil myself?

You can usually remove loose debris and, if the owner’s manual permits it, gently rinse accessible coil surfaces with a garden hose after turning the system off. Do not use a pressure washer, open electrical compartments, or work around wiring. Severe dirt, bent fins, coil damage, or persistent poor cooling needs professional service.

Why does the breaker keep tripping when the AC starts?

A recurring trip may indicate a short circuit, failed capacitor, locked or failing compressor, damaged wiring, or another electrical fault. Reset a clearly tripped breaker only once if you are comfortable doing so. If it trips again, leave it off and call a qualified technician; do not bypass the breaker.

Why is my portable AC blowing cold air but not cooling the room?

Check the exhaust hose for leaks, kinks, crushing, or blockage; seal the window panel; clean the intake filters; close doors and windows; empty the condensate tank; and confirm the room is within the unit’s rated area. A portable unit may discharge cold air but lack enough net capacity if hot exhaust escapes into the room or the space has substantial heat gain.

Is a 20-degree temperature difference proof that the AC is working correctly?

No. A return-to-supply temperature difference is only a clue. It changes with humidity, outdoor temperature, airflow, load, equipment design, and operating conditions. ACCA cautions against treating the 15–20°F rule as universal. A technician should compare measurements with verified airflow and manufacturer performance data.

Should I replace an old R-22 or R-410A system?

Not automatically. Existing systems may be repaired and used, but refrigerant availability, repair cost, equipment condition, efficiency, sizing, and current EPA rules matter. As of August 10, 2026, EPA guidance generally requires new residential split systems installed after January 1, 2026, to use refrigerant below a specified GWP threshold, while distinguishing new installations from repairs. Check current EPA rules and obtain a properly sized replacement proposal before deciding.

Can I add refrigerant to my AC myself?

No. Refrigerant recovery, charging, and opening covered stationary-equipment circuits require appropriate EPA Section 608 certification and specialized equipment. The wrong refrigerant or an unapproved flammable substitute can create fire, explosion, equipment, and legal hazards. Have a qualified technician diagnose the charge and repair any leak.

The Bottom Line

Start with the thermostat, filter, registers and returns, visible power, outdoor-unit clearance, ice, and condensate. Those checks can solve a maintenance problem or give a technician useful evidence. Stop operating the system when it freezes, trips a breaker, leaks indoors, smells electrically burnt, or requires refrigerant or component testing. A lasting repair depends on finding the actual cause—airflow, coil, drain, electrical, refrigerant, ductwork, sizing, or building-envelope—not simply adding refrigerant or replacing the largest part.

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