Difficult company to deal with. With hundreds of options in service providers to choose from you can find an easier company to deal with. I manage many units here in las vegas, and once in a while you are forced to work with obstinate people. This is one such situation. The warranty company forced us to use Air Pro Masters, in my experience HVAC companies branch out to plumbing to make ends meet in the off season and therefore don't usually attract the brightest bulbs on the plumbing side.
The apartment in need of repair is empty and has various contractors coming and going performing the work they need to do. Air Pro Masters refuses to show up unless there is someone there holding their hands the whole time the repair guy is there. This would never be a problem with a respectable company. My advice is stay with the plumbing pros and stay away from air pro, unless you can sit around and wait all day for a part time plumber to show up.