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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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My aprilaire 3 zone controller closes both dampers when both

Customer Question

My aprilaire 3 zone controller closes both dampers when both tstats call for heat. When only 1 calls for heat it seems to work fine as that zone opens and other zone closes. When both call for heat at same time they both close! Any idea why? Polarity on my 24 v trans?
Submitted: 1 year ago.
Category: HVAC
Customer: replied 1 year ago.
Expert:  Phil replied 1 year ago.

Hello, I just saw your question, I am working on it. Tell me about how old your system is, so far it sounds like zone control board might be going bad.

If it worked earlier, the polarity is probably OK.

Please attach a well focused, close up photo of the zone control wiring diagram glued inside the service panel, the picture needs to be taken from straight on, in very good light.

You can use the paper clip- icon at the right end of thetool bar at the top of this dialog box to attach it here. ,Include a picture of the thermostat wire connections to the printed circuit board in the same area.

If there is no paper clip-icon, look for the '+attach files' link at left of your send button.

I can mark it up with trouble shooting instructions.

Customer: replied 1 year ago.
This is a brand new bryant furnace with an N coil in line for cooling (not necessary as it is now cold outside). The zones have just been installed and were working fine. 2 nest thermostats. I don't think both zones ever called at same time to this point. Now both zones close if both call at same time. 1 at a time, no problem, both together, both closed.
Expert:  Phil replied 1 year ago.

Hello, as a rough initial guess, I would say that this is some sort of electronic glitch due to use of Nest thermostats which may not be compatible with some variable speed furnaces.

Solving that problem is going to a very sharp controls man, on site with instruments.

If you can send me a photo of the zone controller with the wiring in place I can look it over for you however. We might get lucky.