I have a newer trane xv95, mated to a 15 year old single stage trane air conditioner in three zones. Last summer the air conditioner worked great. The heater works great – I set the honeywell TZ-4 panel to first stage for one zone, second stage for 2-3 zones.
This early summer/spring the air conditioner works well, but after 1 ½ hours or so, the fan speed slows down, and cooling of the house slows. I know this because the weighted bypass damper arm falls down/closes implying that there is much less pressure in the system. If I turn the unit off for 15 minutes, and restart --- the pressure/fan is back to full speed for another other hour or so.
Thank you so much for your time. The service tech said that the air conditioner is working perfectly, but I didn't realize at the time that I should have turned the unit on for a few hours before he came out). Any hints I could give him when he returns would be appreciated.