LOW COOL & RUNS TOO MUCH - Low cooling is commonly caused by a functioning system that has some type of abnormality that is keeping it from producing its full amount of cooling. There are several factors that should be taken into consideration.
POSSIBLE PROBLEM & DESCRIPTION
Dirty or Restricted Outdoor Coil
If the outdoor unit is operating and the air that is being discharged is very warm or hot, that can indicate low airflow across the outdoor coil. This may be caused by debris build-up on the outdoor coil or other sources of restriction.
Dirty Indoor Coil / Clogged Air Filter
An air conditioner removes heat from the space as it blows air across the indoor coil. A properly operating system should drop the air temperature 15 – 18 deg. F. If the air temperature is very cold (high temperature drop), this can indicate low airflow across the indoor coil which can be the result of a clogged air filter, blocked registers, or a partially frozen indoor coil.
Most new air conditioning units have a condensate overflow switch which shuts-off the air conditioner if the drain line becomes clogged to prevent water damage.
Supply Duct Issues
If there are specific registers that produce very little or no airflow (while others seem sufficient), this would likely indicate either restricted or disconnected supply ducts.
Return Duct Issues
Units that have difficulty cooling on very hot days often have return duct issues (especially when the ductwork is in an attic). Openings in the return ductwork draw-in hot air, making it very difficult for the air conditioner to cool the space. This would be indicated by a high return air temperature when tested at the filter or in the duct entering the furnace or air handler.
Refrigerant Issues - Qualified Technician Recommended
An air conditioner removes heat from the space as it blows air across the indoor coil. A properly operating system should drop the air temperature 15 – 18 deg. F. If the air temperature is not very cool (low temperature drop), that would likely indicate a problem with the refrigerant charge or the refrigerant circuitry.