Window AC Running but Not Cooling (or Not Blowing Cold Air)
Start with the boring things, because they're usually it. GE, Frigidaire, Midea, and LG list the same causes in roughly the same order: the unit is in FAN mode or the set point is above room temperature; the filter hasn't been cleaned in 30 days; the outdoor coils are packed with dirt; the indoor coil has iced over (dirty filter, or outdoor air under about 70 °F); Energy Saver mode has the fan cycling off so it feels like nothing's happening; the room is bigger than the unit; or hot air is leaking in around the unit. A room AC should drop the air passing through it by about 17–20 °F — measure that before you conclude anything. Low refrigerant is real, but it's the last item, and on a $300 window unit it's a replacement, not a repair.
Most likely causes, in order
| Cause | How to confirm | Fix | DIY? |
|---|---|---|---|
| Wrong mode or set point | Display says FAN or DRY; set temp is at/above room temp | COOL mode, set point well below room temp; lowest setting = max cooling | DIY-friendly |
| Compressor restart delay | Just changed mode or settings; fan runs, compressor silent | Wait 3 minutes (Midea manual) | DIY-friendly |
| Dirty filter | Gray, furry; last cleaned more than 30 days ago (GE) | Wash, dry, refit | DIY-friendly |
| Dirty outdoor (condenser) coils | Fins on the back matted with dirt, lint, cottonwood | Vacuum with a soft brush (GE); coil cleaner spray | DIY-friendly |
| Iced evaporator | Frost/ice on the indoor coil behind the filter | FAN ONLY until melted; then fix airflow or set point (Midea, GE) | DIY-friendly |
| Outdoor temperature too low | Under 70 °F cooling capacity drops; under 50 °F the compressor may not run (GE) | Use FAN; it's not a fault | DIY-friendly |
| Energy Saver / ECO mode | Fan stops with the compressor; cycles a couple of minutes every 10 (Midea) | Switch to normal COOL if you want constant airflow | DIY-friendly |
| Undersized unit / heat load / open windows / poor seal | Runs nonstop, room never reaches set point; gaps around the unit; sun on the room | Seal the gaps; shade; size-check with the BTU calculator | DIY-friendly |
| Low refrigerant / compressor fault | Everything above ruled out; coil never gets cold; compressor hums then clicks off | Sealed system — EPA 608 tech or replace | Licensed pro / dealer |
Check these first (five minutes)
- Mode and set point. Midea's first FAQ answer: "Check that your unit is set to 'Cool' mode and the temperature is set lower than room temperature." On a knob unit, GE says the highest number (coldest) gives maximum cooling; on a digital unit, the lowest set temperature does. Then "listen for the sound of the compressor. It will give off a humming noise."
- Fan only, no hum → keep going. Hum present → skip to step 4.
- Three-minute rule. Midea's manual: after a mode change, the compressor waits about three minutes before restarting. Wait it out.
- Room already cold? GE: "If the room is already 64 degrees Fahrenheit or below, the thermostat cannot turn on the compressor." Midea: cooling won't occur below 60 °F room temperature. Not a fault.
- Measure the temperature split. Point an infrared thermometer (or hold a probe) at the intake grille and the discharge. Frigidaire's guidance: the unit should drop the air about 17–20 °F. A split of 15–20 °F on a hot day means the AC is working and the problem is the room; a split under 10 °F means the AC is the problem.
- Filter. GE: cleaned in the last 30 days? DOE: a dirty filter can cost 5–15 % in efficiency, and it's the first step toward an iced coil. Wash it, dry it, refit it. LG: vacuum or soft brush, neutral detergent if it's bad, no water over 104 °F.
- Ice on the indoor coil. Pull the filter and look. Ice = airflow or temperature problem. Midea's manual: switch to FAN ONLY until it melts, then run COOL with a clean filter and a set point that isn't absurdly low. If the outdoor air is under 64–70 °F, the coil will keep icing — use FAN on cool nights (GE, Midea).
- Outdoor coils. Pull the unit or open the back. GE: "Check the outdoor coils (on the rear of the unit) regularly for dirt buildup. If dirty, vacuum with soft bristle brush." DOE suggests keeping vegetation two feet back from the condenser side. A coil cleaner spray and a fin comb fix most of these in 20 minutes. Bent fins block airflow the same as dirt.
- Louvers and obstructions. Frigidaire: louvers aimed so cold air blows back into the unit's own intake short-cycle it; curtains, blinds, or furniture in front of the unit do the same. LG asks for about 8 inches of clearance around the unit.
- Heat load and seal. Frigidaire: "The unit will struggle to maintain temperatures if new air is constantly entering the room." DOE: at the start of each season, "inspect the seal between the air conditioner and the window frame." Check the accordion side panels (foam-fill them), the top sash gap, and whether the sun hits the unit's back all afternoon. Close the door to the room.
- Is the unit big enough? GE: "Make sure the Air Conditioner is properly sized for the room and not too small." ENERGY STAR's table: 150–250 sq ft wants 6,000 BTU; 350–400 wants 9,000; 450–550 wants 12,000; add 10 % for a sunny room, 4,000 BTU for a kitchen, 600 per person over two. Run the room through the BTU calculator. An undersized unit cools the air passing through it fine (good split) and never catches up with the room.
- Everything checks out and the coil is still warm? That's the sealed system. Stop here.
Brand-specific notes
GE
GE's articles are the most specific about temperature: under 70 °F outdoors limits capacity; under 50 °F the compressor may not come on; the unit isn't designed for freezing conditions; and in Energy Saver (SAVE) the fan cycles with the compressor, so "there will be a larger variance in the temperature since there is no circulation of cool air in the room with the fan off." If the unit cycles on and off too often, GE says it may be oversized, not undersized.
Frigidaire
Frigidaire's article adds the winter-cover check (people forget to remove it), the louver angle, and the room being enclosed and insulated. Its next step after these is service — within 30 days the installer, after that Frigidaire.
Midea (including the U-shaped unit)
Midea's manual troubleshooting for "cooling but room too warm": outdoor temperature below 64 °F (switch to FAN ONLY), dirty filter, thermostat set too cold (icing), louvers, blocked intake, open doors/windows. In ECO mode the fan runs three minutes after the compressor stops, then two minutes every ten. The U-shaped unit's error codes are EH/EL/EC/PH/PL/PC plus digits; the manual says to wait about ten minutes because they may clear on their own.
LG
LG's list is about installation: the insulator and mounting plate not fastened, a double-glazed window with the outer pane closed so heat can't escape, the unit used in too large an area, filter dirty, unit too close to a wall (keep about 8 in. / 20 cm clear).
When it's the sealed system
A window AC isn't designed to be recharged in the field. If the compressor runs and the evaporator never gets cold — or the compressor starts, strains, and clicks off on its overload every minute — the refrigerant is low or the compressor is failing. Diagnosing that properly means gauges and an EPA Section 608 certified technician; fixing it means brazing, evacuating, and recharging. DOE lists "check for correct amount of refrigerant" and "test for refrigerant leaks" as professional-technician tasks. On a $250–$500 window unit the service call alone approaches the price of a new one.
Repair or replace?
Cleaning, sealing, and re-siting are free or nearly so, and they fix the majority of "not cooling" complaints. A capacitor or fan motor on a larger unit can be worth a $150 repair on a $700 18,000 BTU model. Refrigerant loss or a compressor is a replacement on anything under about 15,000 BTU and a hard look on anything above. When you replace, buy the right size (not the biggest — DOE notes an oversized unit cools too fast without dehumidifying) and check the running cost of the size you're considering; a 12,000 BTU unit at 8 hours a day is a visible line on the bill.
When to call for service
- Compressor hums, strains, or clicks off repeatedly, or never starts on a warm day with a clean filter.
- Temperature split under 10 °F with clean coils and filter.
- Burning smell, tripped breaker, or a hot plug/cord.
- Under warranty — GE, Frigidaire, LG, and Midea all route these through their own service.
Parts and supplies mentioned on this page
Coil cleaner and a fin comb handle cause #4; foam seal kits handle cause #8; the IR thermometer answers the "is it actually cooling?" question in ten seconds.
- Coil cleaner spray (no-rinse, for AC condenser coils)Check price on Amazon
- Coil fin combCheck price on Amazon
- Window AC side panel insulation / foam seal kitCheck price on Amazon
- Infrared thermometerCheck price on Amazon
Related symptoms
An iced coil has enough of its own causes to deserve its own page (freezing up — coming). Portable ACs share most of these causes and add hose and drain problems: see Hisense E5 and Midea P1 for the water-full codes that stop cooling outright.
Sizing an AC for the room?Air Conditioner BTU Calculator The ENERGY STAR sizing table with its sun, people, and kitchen adjustments.Frequently asked questions
Why is my window AC running but not blowing cold air?
Check mode (COOL, not FAN), set point below room temperature, the three-minute compressor delay, then the filter and the outdoor coils. Measure the split between intake and discharge air: 17–20 °F is normal; under 10 °F means the unit itself is the problem.
How often should I clean the filter on a window air conditioner?
GE says within the last 30 days; DOE says every month or two during the cooling season. Wash in warm water, dry fully, refit.
Why does my window AC ice up?
Low airflow (dirty filter, blocked coil), a very low set point, or outdoor air under about 64–70 °F. Run FAN ONLY until it melts, then clean the filter and raise the set point.
Does Energy Saver mode make the AC cool less?
It cools the same but circulates less: the fan stops when the compressor stops and only cycles on periodically to sample the room. GE describes wider temperature swings in this mode; Midea says the fan comes on intermittently to check the room. Switch to normal COOL if you want constant airflow.
Can I recharge a window air conditioner myself?
No. The units aren't designed for field recharging, and the work requires EPA Section 608 certification. Out of warranty, low refrigerant means replacement.
What size window AC do I need?
ENERGY STAR's table runs from 5,000 BTU for 100–150 sq ft to 12,000 for 450–550 and 18,000 for 700–1,000, with adjustments for sun, people, and kitchens. The BTU calculator applies the table and the adjustments.