I'm a native Phoenician, so over the years I have had my share of experiences with air conditioning issues. I've used a couple of services providers consistently but had become more than a little disillusioned with them recently and after some digging for references settled on R&R Refrigeration. I have to say I was really pleased.
They've been to my house three times (including the initial inspection) and each time they were right on schedule. This is a huge peeve of mine; I don't like being given the four to six hour window. Each time I was given a two hour block and they actually were at my house within 20 minutes of the "as early as" time.
The service has been stellar. I had my evaporative cooler replaced and they did the pre-season tune up on my A/C. When I had questions about my new system, they were quick to respond to my inquiry and had a service man come out to check things out on the next business day.
Add to this that for the cooler they were about 40% less than the nearest quote and I think they might have themselves a life long customer. :)