Okay. Yesterday I asked about noise like "popping" or "fizzing" in the refrigerent line. At the time, the AC was working okay. This was a replacement, low-tier Carrier condenser unit installed a few days earlier.
This morning, the compresser quit. The thermostat was calling for cold, the condenser fan was running, but the compresser wasn't (couldn't hear it, no refrigerent noise, no cold air, tubing on both sides of the expansion valve were room temperature). Hours and hours later, the compresser started working again. The refrigerent noise started out as I'm accustomed to hearing... it sounded like water running through a pipe. About 10-15 minutes later, that same popping and fizzing noise returned, alternating with the normal sound. For now, I have AC again but I don't know for how long (and it's 90 degrees outside).
Any thoughts about this chain of events? By the way, the contractor's weekend tech and then the owner himself have been just insulting on the phone, refusing to believe that the AC wasn't working, and demanding "evidence" to the contrary.