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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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The HVAC system is controlled by a Lennox Harmony III

Customer Question

The HVAC system is controlled by a Lennox Harmony III Control Panel. There are four zones. On several occasions, the panel indicates a zone is open (the red light is off), but the damper is closed as the airflow is going to the bypass outlet and no air is going to the open zone registers. The system default is to have all dampers closed until a message from a thermostat causes one to open. It doesn't appear that the damper(s) are sticking. This problem has happened to two of the four zones. The problem is intermittent. Any ideas?
Submitted: 1 year ago.
Category: HVAC
Expert:  Phil replied 1 year ago.

Hello, the fact that the problem is *intermittent* points directly and almost without exception to bad printed circuit card in the zone control panel.

Use a hair drier to slowly warm the printed circuit card up to 120F or a bit warmer, but not over 140F... if there is any change in the error codes or other system behavior... the card has a cracked micro circuit that opens and closes as the card expands and contracts... that proves a bad printed circuit card.

No change does not prove the card is good however... but a change proves the card is definitely bad.

Let me know what you can discover.