This happens because only one side of the room has a condition side adjacent to it. Meaning the garage underneath isn’t cooled. This factor means that this room has more heat entering it from more sides compared to interior rooms. While each house and situation is different and would need a Technion to come and examen the situation. Possible solutions could be to condition the garage or add a mini split to the room.
First the inhouse filters should be looked at monthly. If they are dirty, then they should be changed. The longest you should go in between changing filters is three months. Except for whole house filters that should be checked every 6 months and changed once a year. It is recommended for the entire HVAC system to be maintenance fully every year. This is normally broken down in two visits. One focusing on the air condition before summer and another focusing on furnace before winter.
If you are getting your system maintenance every year, then you should be fine. The outside unit needs to be able to move air across it. When bushes are planted too close to the unit. The leaves block the air flow. Lower efficiency of the unit and make it run longer and harder. Increasing the chance of it breaking down and needing a repair.