Air Conditioner Blows Warm Air (or at least not cool)

Small window units/wallshakers use the condenser coil to evaporate the3 condensate that the cold evaporater produces when de humidifying the air, as does a cold can of coke . this condensate works its way to the rear/outdoor section of the unit where the hot condenser coil is, the condenser fan blade has a splash ring attached to the perimeter and flings the conensate upon the face of the condenser coil, thus evaporating the condensate while subcooling the liquid refrigerant somewhat. The problem is the pan gets dusty and dirty from exposure and the condenser fan pulling air through the unit and drawing in the outside air and rejecting it through the condenser coil.
The dirt becomes a semi mud or the coil gets plastered with what seems to be mud in a circlar ring matching the condenser fan blades perimeter, thus slowing/stopping the air flow through the condenser coil, and inhibiting the
hot refrigerant gas from being condensed to a liquid, and any subcooling as well. this is not good for acheiving the Temperature differentials (Delta T) from the return vs supply airs temps. Ballpark Delta T is 20 degrees difference from the air in to the air out, indoor air I am speaking of , of course.Design conditions are 95F ambient outdoors with a 80F indoor temp and a 60F air supply furnished by the unit to the room. The last thing you want or need to do is pierce a sealed system! they dont leak unless very old and coroded, or damaged by trauma.
and the piercing is not a good thing to leave on afterwards, a silflossed access is best to install after this type of servicing, and the cost of the job usually exceeds a new unit at that juncture. A 1 yr old unit not damaged in some way wont leak.
and besides they are a critical charged unit with mere ounces of refrigerant, a few ounces will make them stop cooling altogether and burn out the compressor by cycling onnthe thermal overload internally , the refrigerant returning cools the windings normally so the loss of refrigerants not normally the real issue, but chemically cleaning both coils is! Every yeat they need to be removed and slightly dissasssembled usually to allow acces to the interior aspect of the condenser coil as from the outside the apperance wil be fine, but airflow reduced to little or nothing, this alone ill do what you have going on.
Remember that 400 sq ft per ton is a rule and so is 20 degrees differntial from the air in to the air out, By out meaning out tom the room! If you have 20degrees oer close to it, your not too off, and if the outdoor is below 95F and or indoor is warmer than 80 your results may not be 20 degrees until the parameters change.

Blowing warm air, can be a Thermosatic problem or other electrical trouble, Burn wire off control (stat) or Compressor or a bad capacitor. If your not good with repairs on A/C please call a rep.firm
Depending on the age of the Unit - ASK ! HOW MUCH THE REPAIR WILL COST . Some times it pay to repair - condition of the Unit is important too . Good Luck EM

When serviced by a qualified service tech who finds and repairs a leak before recharging a system it is not illegal. However with the age of your unit you may want to balance the possible cost of a new unit against the cost of repairs to the old one. After repairs are made to an old unit you still have an old unit.