I live in Phoenix. Over the summer, I had some water dripping from the air handler in the attic, causing a wet spot on the drywall below it. Short story is contractor (sent by warranty co.) determined it was water blowing from drip tray into ductwork due to powerful airflow over drip tray and no baffle to stop it. He said that since parts aren't available for the circa 1993 unit he would simply drop fan speed to 1/2, preventing blowing of water and enabling it to drain out (drain was clear). AC worked, still, but didn't cool the house as fast as it had been able to before. They sent three different guys (first guy thought it was a sweating cold refrigerant pipe, which it wasn't), and I finally gave up on worrying about it, as the leak stopped.
Now, it's winter, and we've had some record cold (for Phoenix) with lows in the mid to high 20's. Cold enough to freeze my water pipes in the early AM! The problem is the gas heat system has been struggling to warm the house. The fan speed appears to be very low -- about 1/2 that of the already lowered AC speed, and if memory serves, about 1/2 of what the heat formerly was last winter season. It's so quiet I hardly hear it, and I barely feel flow when it's on. When it runs, the areas of the house away from the thermostat, which is in the hallway by the bedrooms, is frequently much colder than the main living area, which finally does seem to get a bit warmer, but only after a long time of running. During the nights in the upper 20's, it was really cold in the bedrooms, where almost no airflow came out of the ceiling-mounted ducts. I have a feeling the heat just stayed near the ceiling.
I called the warranty co. and they spoke with the HVAC company that they work with, who agreed to send their "senior tech", who is here now. He turns out to be one of the same guys who had come originally in the summer and thought the freon tube was sweating. He is telling me that the fan has to be lower or else it will cause the heater core to crack due to condensation or getting too hot (I didn't know condensation was an issue with a heating core).
In case anyone wants to read the summer thread, here it is: http://hvac-talk.com/vbb/showthread....his-assessment
Thanks for the input!