If this has occurred on the ducts leading to the upper floor registers that is your answer.
How to get ac to upper floor.
This forces greater volumes of cooler air higher in the air column of the home.
Hot air rises and when the outside temperature is hot you must adjust your vents to force the cool air to the upper floors.
You will need to adjust you vents in the summer months in order to keep.
Make the second floor return vent duct bigger.
How to improve central air on upper floors.
If a heater or air conditioning unit sits in a basement and is separated from an upstairs bedroom by a garage attic and or crawl space air can get lost in those areas along the way reducing the amount of cool air that makes it to the upstairs room.
Keeping upstairs rooms adequately cooled in summer puts the homeowner up against a basic fact of physics.
If that happens the disc shaped dampers inside the ducts may prevent much of the normal airflow.
Add a small return vent duct to each room on the second floor.
The air conditioner also may not be of sufficient tonnage to remove the heat from the home.
The drawback to this method is the decrease in temperature at the lower level of the home.
Too often these inadvertently get bumped so that the metal tabs are perpendicular to the ducts.
Some people simply turn down their air conditioner but then utility bills climb and the first floor gets too cold while the upstairs is still too warm.
Turn the air conditioning temperature down.
You might also want to try adding a ceiling fan in.
Sometimes the difficulty is caused by leaky joints ducts or even the layout of a home.
For 1 the furnace fan running all day with the a c on might solve some milder heat trap problems for your second floor.
Upper floor rooms can be difficult to heat and cool.