Basically everything appears to be running properly but the unit is cooling only 1 room out of 4.

This is our upstairs unit which has always been outstanding/reliable.

This spring I noticed that it didn't quite seem as cool as usual and now that the heat has come it is hovering around 80 during the day and won't get cooler.

Condenser coils are clean, filters are good. My first thought is obviously a leak and maybe we need a charge.

What I'm confused by are the differences in temperature out of each vent. I checked the attic ducts for leaks and did not notice anything.

There are only 5 vents/registers up there. I measured the air output temperatures and this is what I found.

Thermostat reads 80. Set to 72
Bedroom 1 reads 80
Bathroom reads 81
Bedroom 2 reads 75
Bedroom 3 reads 68

So there is cold air blowing into 1 room and partially colder in another. I plan to call someone out but I always try to figure things out and this just baffles me

Anyone have any thoughts?

I saw a video that it could be a bad relay but I also found all sorts of things it could be.

Longer runs with more heat gain vs. shorter?

The room that is cold has a longer run than 2 of the others...probably by almost double.

if you are getting cold air in one room then i doubt you need a charge. this seems like an airflow problem. are you getting good flow out of the vents in each room?

Yes the air flow seems to be normal but I'm not up there too much to notice I guess. I'm gonna go poke around a bit more before I call.

Where are the return air vents? No easy path for return air in certain rooms, especially with doors closed = less supply into those rooms.

open all the doors to each room, open all the vents...let things run and stabilize - this should help identify airflow issues. If you still have cold air on one room but not others...that is strange

Also - I was up in an older house attic at a relative's house and the ductwork attached to the vent in one room had come loose/fallen off, so there was no cold air being sent into the room via that vent. Odd thing, but something to consider

Is there any kind of dual zone set up in your house? In my last house, it had dual zones, and I was getting no air from the upstairs vents. It was a damper motor that failed which was blocking all the airflow to those vents.