We're renting a home with a bonus room over the garage - our daughter uses it as her bedroom. The HVAC system is <1 year old and keeps the lower level of the home very comfortable. The problem is the bonus room / bedroom. When the outside temperature gets to the low 90s , the AC can't keep up.

The homeowner had a zoned system installed, so the bonus room has its own zone and thermostat separate. The room also has a return register. Is there anything we can do to cool the room short of requesting insulation be added to the garage ceiling attic and / or requesting a ductless mini-split in that room? I'm wondering if the zone dampers can be adjusted to allow for more air flow to the bonus room, or we adjust the downstairs vs. bonus room temp settings, or we set the bonus room thermostat to have the fan always running?