I think with any kind of service agency like this you're bound to get a few mixed reviews due to the complexity of what's being worked on in the wide range in skill and personalities. That said, we had a problem with our air conditioning unit in our new home and contacted Sierra through our builder's customer service warranty center.
Sierras's customer service was able to get us an appointment quickly and the technician, Adam, who arrived was courteous professional and got immediately to work.
He perform a full inspection answered a number of questions we had about the unit and found a few wiring problems which was causing the air conditioner to not properly run. In less than 45 minutes he had completed the repairs tested the unit and it was blowing very cold air and working perfectly.
I have no problem with recommending this company and their service and a special thanks to Adam for doing such a great job.