I have a 3 zoned air conditioning system with 3 thermostats each controlling a damper. Startup works OK for when any of the thermostats call for air. The blower starts up and simultaneously the appropriate damper(s) is opened. Everything works OK until all zones are cooled and all thermostats have requested that their dampers be closed. While all dampers are closed, the blower remains running for a minute or two. Since the blower has no where to move air, the blower accelerates in speed with a like high whining pitch sound. The trunk between the furnace the dampers expands like a balloon as the air has no where to go. Eventually the blower shuts off. The trunk near the furnace then 'pops' back to its normal size as the air pressure is reduced.

Is the normal or should the blower be turned off as soon as all dampers are closed?

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Originally Posted by bidder_upupup

I have a 3 zoned air conditioning system with 3 thermostats each controlling a damper. Startup works ok for when any of the thermostats call for air. The blower starts up and simultaneously the appropriate damper(s) is opened. Everything works ok until all zones are cooled and all thermostats have requested that their dampers be closed. While all dampers are closed, the blower remains running for a minute or two. Since the blower has no where to move air, the blower accelerates in speed with a like high whining pitch sound. The trunk between the furnace the dampers expands like a balloon as the air has no where to go. Eventually the blower shuts off. The trunk near the furnace then 'pops' back to its normal size as the air pressure is reduced.

Is the normal or should the blower be turned off as soon as all dampers are closed?

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The blower shut down control/relay is defective OR you need to ad one to your system. Actually in today's world you should be running a modulating blower that only supplies enough air for each zone as it is activated. That style control also shuts down the blower when all zones are satisfied. See a HVAC specialist for this system to be installed.