I've had two different companies come look at this "problem" and both have not been able to figure out a solution, other than just replace major components. The reason i use quotes is because the unit itself (one unit, two zones, upstairs/downstairs) is cooling just fine, even on 100+ degree days. Refrigerant levels are fine, no leaks, coil isn't frozen over, no blockage, etc. The strange behavior that is occurring, however, is that intermittently the air will just stop for a fraction of a second and then keep going like nothing happened. Some days it happens once every few minutes, other days it happens once every few hours and it is definitely not a short cycle. I can't find any way to replicate it or make it happen on purpose. Bear in mind it literally happens for a fraction of a second. Just turns off (air stops coming through the vents) and then immediately back on. The only other thing i noticed is that the unit in the attic does make an audible noise when it stops but it's so quick to come back on that it's difficult to describe it. Best i can say is that it sounds like a deep bass sound you might hear if your neighbor was playing their stereo too loud.
I don't really know what to do since, aside from the random starting/stopping, the system seems to be working perfectly. My concern is that if i don't address it now it might turn into something major later. Has anyone heard of anything like this before? The two people i had come and look at it both said they had never seen anything like it before. Thanks in advance.