HVAC
The AC is running but the house is not cooling
The short version
Check airflow before you check anything else: thermostat mode, filter, vents, and the outdoor unit. A frozen line or a tripped breaker needs the system shut off and a call. If air is moving but only slightly cool, the problem may be the charge, the ducts, or the house itself.
The air conditioner is doing something. You can hear it. The thermostat is set to a number the room has never reached, and the vent is moving air, but the air is not cold enough to matter. By late afternoon the house is warm and the system is still running.
That gap between "running" and "cooling" is the whole diagnosis. A central air system has to move air, remove heat, and get rid of that heat outside. If any one of those steps fails, the equipment can sound perfectly healthy while the rooms stay warm. Your job is to figure out which step is failing, and which of those failures you can safely touch.
Start with airflow, not temperature
Put your hand near a supply register for a full minute. Is the air moving strongly, weakly, or not at all? Then check a return grille. A system that cannot pull air back cannot push cold air out. Weak airflow at every register points to a filter, a blower, or a duct problem. Strong airflow that is only mildly cool points toward the outdoor unit, the refrigerant circuit, or the house itself.
| What you notice | What it often means | What to do |
|---|---|---|
| No air from any vent | Blower, breaker, or control problem | Check breaker and thermostat, then call |
| Weak air everywhere | Clogged filter, failing blower, duct restriction | Replace filter, open vents, call if unchanged |
| Strong air, barely cool | Outdoor unit not running, low charge | Check outdoor unit, call for service |
| Cool for ten minutes, then warm | Frozen coil or a system protecting itself | Turn cooling off, run fan, call |
| Ice on the copper line or indoor coil | Restricted airflow or low refrigerant | Stop cooling, thaw, call |
| Water at the indoor unit | Clogged condensate drain or float switch | Turn system off, call |
| One room warm, others fine | Duct, damper, or return-path issue | Check vents and doors, ask for a duct check |
The checks you can do safely
Thermostat
Confirm the mode is cool, not fan-only or heat. Set the fan to auto rather than on; continuous fan runs the blower without cooling and can make the air feel warmer because it is recirculating room air. If the thermostat is on a schedule or a hold, clear it. Replace batteries if the display is faint. A thermostat that is mounted near a lamp, a vent, or direct sun can read the wrong room and stop the call for cooling early.
Filter and vents
A dirty filter is the most common cause of weak airflow, and weak airflow can eventually freeze the indoor coil. Pull the filter, hold it up to the light, and replace it if it is loaded. Then walk the house and make sure no register is closed, carpeted over, or blocked by a sofa. Do not close off a large share of the vents to "focus" cooling on one room; that raises pressure in the ducts and can reduce total airflow.
The outdoor unit
Look at the outdoor unit from a safe distance. Is the fan spinning? Is there a clear space around it? Is the coil packed with grass clippings, dryer lint, or cottonwood fluff? Is the disconnect switch pulled? Is the breaker at the panel tripped? If the fan is not moving but the compressor is humming, shut the system off at the thermostat and call; a compressor that runs without fan airflow can be damaged quickly.
The condensate drain
A central system removes moisture, and that water has to go somewhere. If the drain line is clogged, a float switch may shut the system down, or water may pool near the indoor unit. If you see water, turn the system off at the thermostat and call. Do not ignore a slow drip; it can reach ceiling drywall and framing.
If you are already in it
The desk is open 7am–10pm ET, seven days a week. Call (877) 454-8068 and describe what is happening. The call is free; the independent professional sets their own charges.
Ice on the line is a symptom
Ice on the large copper line, the indoor coil, or the outdoor unit is not a reason to add refrigerant. It is a sign that the coil is too cold, usually because airflow is restricted or the charge is low. Turn the cooling off, set the fan to on so the coil thaws, and leave the system off until a technician looks at it. Thawing can take hours. Putting a pan under the drip and checking it is reasonable; hacking at the ice with a tool is not.
If the system ices over again after a filter change, stop running it. Repeated freeze-and-thaw cycles stress the equipment, and running a system with low refrigerant can shorten the compressor's life.
Cool at the vent, warm in the room
Sometimes the air leaving the register is genuinely cold, but the house does not get comfortable. That is a distribution problem, not necessarily an equipment problem.
- Ducts in a hot attic lose cooling before the air reaches the room. Look for disconnected flex duct, crushed runs, or long uninsulated stretches.
- A single return in a closed-off hallway can starve bedrooms when doors are shut. Leave doors open or add a return path.
- West-facing rooms gain more heat in the afternoon than the system was sized to remove.
- Attic insulation and air sealing matter more than a thermostat setting. If the ceiling is warm to the touch, the house is fighting itself. The insulation and energy page covers the upgrades that make a cooling system's job easier.
- Appliances and windows add load. A dryer venting indoors, an oven left on, or uncovered windows during the hottest hours all work against the AC.
What not to do
Do not add refrigerant yourself. Do not cover the outdoor unit to "help" it, and do not hose down a running unit. Do not keep resetting a breaker that trips immediately. Do not run the system with the filter removed; that lets dust straight into the coil. Do not block the outdoor unit with a fence, a tarp, or stored items. And do not assume a bigger unit is the answer; an oversized system cools quickly and leaves the house humid, which feels worse than a slightly warm, dry room.
When to call
Call when the outdoor unit will not start, the breaker trips, ice forms, water appears at the indoor unit, or the air stays warm after a filter change and a thermostat check. Call sooner if anyone in the home is at risk from heat, or if the indoor temperature is climbing into the high 80s with no overnight relief.
If the house is hot and the system is off, close blinds, use fans to move air, and move to the coolest part of the house. A fan does not lower the temperature, but it helps the body lose heat. Do not use the oven, and do not leave a space heater running by mistake because the thermostat is confused.
What to tell the dispatcher
Say whether air is moving, how strong it feels, and whether it is cool at the vent. Mention any ice, water, noise, or breaker trip. Give the indoor and outdoor model numbers if you can read them safely, and say how long the problem has been building. "Cold in the morning, warm by two o'clock" is a useful clue.
Ask whether the visit includes a diagnostic charge and whether the technician will check airflow and charge together. A good cooling call is not just a refrigerant top-off; it is a search for why the system stopped keeping up.
The bottom line
Running is not the same as working. Check the easy things first, especially airflow, and treat ice and water as stop signs. If the system is moving air but not removing heat, the HVAC service page explains what a technician will test. If you are still deciding how quickly to act, call now or wait gives you a simple triage. A house that never cools is usually a system problem with a findable cause, not a mystery.