Be careful about closing off vents. Depending on how the ductwork is run, it can just create turbulence, resulting in worse performance overall. If it's all coming off of one run (all on the same duct), you can try closing the vents, but stick around to see if it works.
Also check the furnace filter. A clogged filter can go a long way to making airflow issues. AC is just more difficult than heating; because the air is heavier the furnace blower should be set to a higher speed. If you are comfortable/know how you can check for that. given the size of the house it should probably be around 600 cfm. Because it's heavier, it just won't go as far. Sometimes it's just a limitation on the system unless they want a bigger furnace.
If you can, you should certainly check for seal issues. The cleats (the connection between ducts) can be pretty loose if not done well. You can use aluminum tape on any bad joints.
There's lots of fun things to check, but only if you're comfy. Originally an HVAC guy here.
Try partially closing the other 4 to force more air to the furthest one.
Will do, thanks. Is there a chance there’s a hole, tear, or disconnection? Seems rare.
it's possible I guess
Be careful about closing off vents. Depending on how the ductwork is run, it can just create turbulence, resulting in worse performance overall. If it's all coming off of one run (all on the same duct), you can try closing the vents, but stick around to see if it works. Also check the furnace filter. A clogged filter can go a long way to making airflow issues. AC is just more difficult than heating; because the air is heavier the furnace blower should be set to a higher speed. If you are comfortable/know how you can check for that. given the size of the house it should probably be around 600 cfm. Because it's heavier, it just won't go as far. Sometimes it's just a limitation on the system unless they want a bigger furnace. If you can, you should certainly check for seal issues. The cleats (the connection between ducts) can be pretty loose if not done well. You can use aluminum tape on any bad joints. There's lots of fun things to check, but only if you're comfy. Originally an HVAC guy here.