A poorly cooling AC unit is just as frustrating as a system that has completely broken down. There are many reasons for poor cooling. Some may handle the repairs themselves, while others may require the assistance of an AC repair service.
1. Blocked Air Flow
Two parts of the HVAC system can lead to blocked airflow through the condenser, which will then result in poor cooling. The most obvious issue is a dirty and blocked filter. Remove the filter and inspect it. If it looks dirty, then it's time to replace it. You should vacuum out the filter slot to remove excess dust as well, just to ensure all potential blockages are removed. The other common reason for blocked airflow is that the wall return is covered. All duct systems have a combination of vents, which is where the cooled air enters the room, and returns, which pull in the warm air to recirculate it through the system. If the returns are blocked by furniture or drapes, then insufficient air is pulled through the system and it cools poorly.
2. Condenser Troubles
The condenser is in the outdoor unit. The fins work to dissipate the heat from the air so it can be sufficiently cooled. A fan transfers this air, so if the fan isn't working then you end up with warm air. A professional repair may be necessary to fix the fan. Some condenser issues are easy to address yourself. If the condenser fins are dirty, your AC may not cool well. You can simply wash off the condenser fins (the vent-like opening on the unit) with water to get them clean. If any of the fins are bent or damaged, then purchase a fin comb from a hardware store to straighten them out.
3. Refrigerant Issues
Your AC unit uses a refrigerant to actually cool the air. Most ACs work with a closed refrigerant system, which should cut down on leaks in theory. The refrigerant is circulated through the system by the compressor. If the compressor fails, then you need to have it repaired promptly. Leaks can also occur. Besides poor cooling, signs of a leak include hissing noises or ice buildup on refrigerant lines and the outdoor part of the unit. If you suspect low refrigerant could be the cause of the cooling issues, turn off the unit to avoid further damage until you can get a contractor out for a repair.
Contact an AC repair service for more help.