Check thermostat, power, breaker, air filter, vents, and the drain; then confirm the outdoor unit runs before calling a licensed tech.
Your apartment feels warm, the AC hums or sits silent, and sweat is winning. Don’t panic. Most no-cool trips start with simple checks you can handle in minutes. This guide walks you through the exact steps that solve the majority of apartment cooling hiccups, plus what to document for your property manager if you need a repair ticket.
What to check when apartment AC is not working: quick wins
Run through these fast checks from easy to hands-on. You’ll learn what’s wrong and, in many cases, fix it on the spot.
| Item to check | Why it matters | DIY or pro |
|---|---|---|
| Thermostat mode and setpoint | It must be on “Cool” with a set temperature below room temperature. Fan set to “Auto.” | DIY |
| Thermostat batteries | Low batteries can stop cooling commands or make the screen go blank. | DIY |
| Power to the system | Tripped breakers, GFCIs, or a switched outlet can kill power to the air handler or condenser. | DIY |
| Air filter | A clogged filter chokes airflow and can make coils ice over or the system short-cycle. | DIY |
| Supply and return vents | Closed or blocked grilles starve airflow and drop room comfort fast. | DIY |
| Condensate drain and pan | A full pan can trip a safety float switch and stop cooling. | DIY |
| Outdoor unit | Leaves, lint, or a yard bag stuck to the grille prevents heat release. | DIY visual |
Thermostat and controls
Set the thermostat to “Cool” and “Auto.” Drop the setpoint at least 3–5 degrees below the current room reading. If the display is dim or the screen glitches, replace the batteries with fresh ones of the same type. If you use a smart stat, confirm it isn’t in an energy-saving away mode.
When in doubt, power cycle the thermostat: switch to Off for 30 seconds, then back to Cool. If controls still misbehave, set a simple hold at your target temperature.
Power and breakers
Go to the electrical panel and look for a tripped breaker labeled “AC,” “air handler,” or “condensing unit.” Flip any tripped breaker to Off, then back to On. Some apartments also have a wall switch near the indoor unit; make sure it’s On. If the air handler uses a GFCI outlet, press Reset.
Air filter and airflow
Pull the filter from the return grille or the slot by the air handler. If it looks dusty or grey, replace it. ENERGY STAR recommends checking monthly during heavy use and changing at least every three months. A clean filter protects the system. Match the size on the frame and point the airflow arrow toward the blower.
Supply and return vents
Open every supply register and the main return grille. Slide furniture, curtains, and boxes away from vents so air can move freely. In small rooms, two inches of clearance helps a lot. If a room still lags, leave its door open for better circulation.
Condensate drain
Find the plastic drain line near the indoor unit. If the pan is full or the float switch tripped, cooling will stop. Turn the system Off, clear standing water, and, if you can reach the tee, pour in a cup of white vinegar. Restore power and try Cool again.
What to do before opening anything
Safety first. Turn the system Off at the thermostat and wait for the blower to stop. Keep hands away from fan blades. Don’t remove service panels. Anything beyond filters, drain pans, and clearing debris should wait for a licensed technician. Snap a few photos of what you see so your building team has details.
Checking an apartment AC that is not working: deeper fixes
Still warm? Work through these next steps to narrow the fault and gather clear notes for maintenance.
Listen for the indoor blower
Stand by a supply vent. If air blows but it’s not cool, you likely have a cooling issue, not a control issue. If there’s no airflow at all, the blower may be off, a breaker may be tripped, or a safety switch may be active.
Check the outdoor unit
Go outside and look at the condenser. The top fan should spin and warm air should blow upward. If the fan runs but the room stays warm, the coil may be dirty. With power Off at the breaker, brush lint and leaves from the fins. Keep tools and weeds away from the grille so air can pass. Leave cabinet cleaning to a licensed tech.
Look for ice
Shine a flashlight at the copper lines near the air handler. Ice on pipes or a frosty coil points to low airflow or a refrigerant issue. Run Fan only for an hour to thaw, install a fresh filter, open all vents, then try Cool again. If frost returns, note the time and room temp in your ticket.
Watch the drain during cooling
After ten to fifteen minutes of steady cooling, a gentle drip at the condensate line is normal. No drip can mean the system never reached dehumidifying mode. Overflow or standing water means the drain is clogged and the float switch will trip again.
Mind indoor humidity
Sticky rooms feel worse even when the setpoint looks right. A simple hygrometer can confirm indoor humidity. The EPA suggests about 30–50 percent. If readings stay high, include that note so the tech checks airflow and run time.
Thermostat batteries and wiring
If your thermostat runs on batteries, swap in new ones. Corroded or weak cells can block the cooling call. If your model uses a common wire, confirm the faceplate is fully seated on its base. Loose pins cause odd behavior.
Smart thermostat sanity checks
Open the app and look for a schedule or geofence that raised the setpoint. Turn off eco modes for the day. If the stat shows “Cooling” but neither unit runs, change to a basic hold and try again. Brand help pages cover reboots and sensor overrides if needed.
Document what you see
Write down the time, thermostat reading, any error codes, breaker status, sounds from the outdoor unit, and whether the drain pan was full. Clear notes shorten repair time and help the building team rule out repeats.
Table of common symptoms and fast next steps
| Symptom | Likely cause | Next step |
|---|---|---|
| Thermostat on, no air at vents | Tripped breaker, wall switch off, float switch tripped | Reset power, empty pan, try Fan then Cool |
| Air blows, not cold | Dirty filter, closed vents, iced coil, outdoor fan off | Replace filter, open vents, thaw ice, check condenser |
| Outdoor unit silent | Tripped breaker, service disconnect pulled, control fault | Restore power at panel if allowed, call for service |
| Water around indoor unit | Clogged drain line or pan | Shut Off, clear water, add vinegar, report clog |
| Unit cycles on and off fast | Dirty filter, blocked return, thermostat placement issue | New filter, clear return, move lamps or heat sources |
| Burning smell at start | Dust on electric heat strips in combo units | Smell should fade quickly; if not, power Off and report |
| Breaker trips again | Short or motor problem | Stop resetting; submit a work order |
Care tips that prevent the next no-cool
Keep a checklist on the fridge and set calendar reminders during peak heat. Swap filters on schedule, keep vents open, and keep clutter away from the indoor unit door so service access stays clear.
Vacuum the return grille every few weeks to keep lint down and help the filter last. Keep the air-handler closet clear so intake air stays steady.
During heat waves, give the system a head start in the morning and avoid big daytime setpoint swings. Closing shades on sun-facing windows helps rooms hold temp. If your building allows box fans, aim one to push cool air from the hallway toward the warm room while the AC runs.
For filters, follow the unit label and your lease rules. The Department of Energy notes that clean filters keep airflow steady, which helps cooling and can reduce service calls. If your lease covers filters, ask the office for the right size and MERV rating.
When to call building maintenance
Put in a ticket when breakers won’t reset, the outdoor fan won’t spin, you see ice after a new filter, water keeps returning to the pan, or the system keeps shutting off. Attach photos of the thermostat screen, the filter you removed, the breaker panel, the drain pan, and the outdoor unit. List any error codes and your steps so far. That information helps the tech bring the right parts.
What not to do
Don’t open electrical panels or push contactors. Don’t bend coil fins with knives or screwdrivers. Don’t block the return grille with a couch. Don’t run the system for hours when it’s iced over. A little patience and a thaw prevents bigger repairs.
Need a quick reference?
Here’s a fast sequence that solves most apartment cooling stalls:
- Cool mode, Auto fan, setpoint a few degrees below room temp.
- Fresh thermostat batteries, then a simple hold.
- Reset tripped breakers and any GFCIs tied to the air handler.
- New filter; open every supply and the return grille.
- Empty the drain pan and add a bit of vinegar to the tee.
- Clear debris from the outdoor unit and confirm the top fan spins.
- If ice appears, run Fan only to thaw, then retry Cool.
One last tip: if you’re home all day, keep an eye on humidity. The AC should pull moisture while it cools. If rooms feel clammy, note the reading and time. That small detail often speeds a fix. For background on humidity targets, see the EPA’s guidance on indoor moisture.
Extra checks for common setups
Heat pump quirk
Many apartments use heat pumps. These can cool and heat with the same outdoor unit. Make sure the mode isn’t stuck in Heat or Emergency Heat. If you switched modes this week, give the reversing valve a moment after each command and avoid rapid mode changes. If the outdoor fan runs but air stays warm in Cool, note the weather and any clicking from the outdoor cabinet.
Window or wall unit tips
If you have a window AC or a PTAC, clean the front filter monthly. Many grilles lift off without tools. Rinse the mesh and let it dry. Make sure the unit tilts slightly outward so water drains outside. Set any “vent” lever to “Closed” on hot days. If the unit ices up, run Fan until it melts, then restart on Cool.
Mini-split heads
Some newer buildings use mini-split systems. Pop the front panel and slide out the washable screens. Rinse, dry, and reinstall. Make sure the head isn’t set to Dry or Fan only. Aim the louvers upward so cooled air mixes across the room.
Shared building systems
In mid-rise and high-rise buildings, a fan-coil may tie into a central plant. Your filter and drain still matter. There may also be a seasonal switchover. If neighbors see the same issue, mention it in your ticket so staff can check pumps and schedules.
Thermostat placement
Lamps, TVs, and sun can trick the sensor. Move heat sources away from the stat and add shade if needed. If the stat sits behind a door or above a supply vent, cool air may short-cycle past the sensor and end cooling early.