Why Is My AC Running but Not Cooling the House?
An AC that runs all day without cooling usually has a dirty filter, a refrigerant leak, or a blocked outdoor unit. Start with the filter and the thermostat. If the filter is clean, the thermostat is set to cool, and the house is still warm, the system needs a technician.
What makes an AC run without cooling?
Dirty air filter
A dirty filter blocks the air moving through the system. It still runs, but almost no cool air reaches your rooms. This is the most common cause we find. Changing the filter is safe to do yourself.
Safe to check yourselfLow refrigerant from a leak
Refrigerant is the fluid that carries heat out of your house. It never gets used up. If it is low, it leaked out somewhere. A low charge makes the AC run long and cool very little, and it can freeze the indoor coil. Finding a leak is technician work.
Technician repairDirty or blocked outdoor unit
The outdoor unit dumps the heat it pulled out of your house. Grass clippings, cottonwood fluff, leaves, and dirt coat it and hold that heat in. You can clear the debris and cut plants back. Deep cleaning of the fins is our job.
Safe to check yourselfThermostat set wrong
A fan set to ON blows room-temperature air between cooling cycles. That feels like warm air at the vents. A HOLD setting or a schedule can also keep the house warmer than you meant. Checking the settings takes a minute and is safe.
Safe to check yourselfFrozen indoor coil
The indoor coil is the finned part your air blows across to get cold. When airflow or refrigerant drops, it can freeze into a block of ice. Air cannot get through, so the system runs and cools almost nothing. You can shut it off to thaw. Why it froze needs a technician.
Technician repairLeaking ducts
Ducts that leak into an attic or a crawl space dump cool air before it reaches your rooms. Older duct runs lose a lot of air this way. We find the leak, show you where it is, and tell you what it is costing you in comfort.
Technician repairFailing compressor or capacitor
The compressor is the pump that moves refrigerant. The capacitor is the part that gives it the push to start. When either one is weak, the outdoor unit hums but does not pump. Inside, the fan keeps blowing, so it sounds normal. Both are technician work.
Technician repairWhat can you check yourself?
- Set the thermostat to COOL and the fan to AUTO. Drop the setting a few degrees below the room.
- Look at the filter. If you cannot see light through it, change it.
- Open every vent. Pull furniture and rugs off the return grilles.
- Walk out to the outdoor unit. Clear leaves, grass, and debris two feet back on every side.
- Hold your hand at a vent. If air is blowing but is not cold after fifteen minutes, stop there.
Safety note: Never open the refrigerant lines or the electrical covers on either unit. Those repairs need a trained technician.
When should you call for repair?
Call when the filter is clean, the thermostat is right, the outdoor unit is clear, and the house still will not cool. Call if you see ice on the copper lines. Call if the outdoor unit clicks or hums but never starts. Call if it runs for hours and never gets there. Running an AC in that shape strains the compressor, and a small repair turns into a big one.
Most Germantown townhomes pull all their return air through one filter grille in a hallway ceiling. When that grille sits above a stairwell, nobody changes it, and the coil upstairs pays for it. The system keeps running and the rooms stay warm. Start there before anyone brings up refrigerant. Germantown also filled in over about twenty five years, so whole streets are on their second system at the same time.
Related questions
How long should an AC take to cool a house?
A healthy AC drops the house about one degree every fifteen to twenty minutes on a normal summer day. On a humid afternoon it takes longer, because part of its work is pulling water out of the air. If the temperature has not moved after an hour of running, something is wrong and the system should be checked.
Can I add refrigerant to my AC myself?
No. Refrigerant handling needs a federal license, and a low charge always means a leak. Topping off a leaking system wastes the refrigerant and leaves the real problem in place. If the charge is low, we find the leak, repair it, and put the right amount back in.
Why is my AC running but the house is still humid?
A cool but sticky house means the system is moving air without pulling out enough heat and water. Common causes are a system too big for the house, low refrigerant, or a coil that is dirty or icing up. In a humid Maryland summer that is worth a diagnostic visit.
Should I turn the AC off if it is not cooling?
Yes, if you see ice on the copper lines or on the indoor coil. Switch it to OFF and let it thaw. Otherwise you can leave it running while you check the filter, the thermostat, and the outdoor unit. If those do not bring the cold back, shut it down so the compressor is not strained.
If your AC is running and the house will not cool, call Mora Heating & Air and we will find the real cause.
Or tell us what your system is doing
Send us the details and we will call you back. If the house is very hot or very cold right now, calling is faster.