I'm gonna call BS on that. If it IS an X13 indoor fan motor they are notrious for these symptoms. Pull the panel off and try to take and post a pic of the motor. I can spot one in a New York minute.
But, I'll admit this can be a very difficult problem unless the tech catches it in action. My daughter used to say "Daddy my car is acting up" and I'd do a test drive and it would would perform perfectly. Sometimes these type of intermittant problems can drive you nuts.
I'll see if i can get a pic of it and post it.
Originally Posted by bobboan
If it's an x13 or ECM, and the static pressure becomes too high when only one zone damper is open, the motor will come to a full stop and restart in order to "reset" itself to the correct cfm.
The zone dampers should be set to a minimum 25% open.
If there's a bypass relief, check it to see if it "bounces" or "flutters" excessively.
Now that is very interesting actually. I generally have the bottom thermostat set to 80 (since i'm hardly ever downstairs) and the top thermostat set to 70-74 depending on if it's during the day or night. What this means is that the top zone is running all the time and the bottom one is almost never running at all, which kind of falls in line with what you're saying.
I have no idea how to check if it's a x13 or ECM but as i said above i'll take a pic and post it so maybe someone can identify it. Is there an obvious way to see what the zone dampers are set to?