Hello,
Writing from Phoenix, AZ. We have a 2-unit system and currently are having a problem with the air coming from just one vent on our home. The unit that produces air for this vent has been serviced twice within the last year. We've been in our home for about 6 years and up until recently the room (large master bath) where this vent is located was always the coldest in our home. I used to close the vent at least halfway or more and it was still the coldest room in the house. Last Sept this unit went out and the tech from the company we used said we needed a new capacitor, so he replaced it and everything was fine.

This spring when we started to use the A/C again I noticed warmer air coming from the master bath vent compared to all others supplied by the unit, which covers 3 bedrooms and baths. The actual air is as strong as it has always been. So, we called the same company that had previously worked on the unit and the tech that came out confirmed that the air coming from this one vent was warmer than all the others. It's not exactly hot air but it's definitely not cold. I'd describe it as just slightly cooler than room temp. My first thought was it might be a leak in the duct work up in our attic space. He took a look and said the duct work was fine and he thought it could possibly be a micro leak in our evap coil in the attic, though he couldn't be sure without doing a nitrogen test. He then charged us to put in freon ($90) saying that it might help but he really didn't know if it would. I didn't notice much of a difference after. He said A/C units can be "funny" at times and this can happen. Needless to say hearing that was a little troubling.

So, I guess my question is if we do indeed have a micro leak in the evap coil leak wouldn't that affect the air going to all the registers supplied by the unit, and not just one? It's just so odd that the master bath area used to be so nice and cool/cold and now it's almost like walking into a sauna. Any ideas at all what could be causing this single vent to have such a different temp compared to all the others? Any help at all would be greatly appreciated. Thank You!