HVAC Blowing Issues

Old 08-02-18, 10:38 AM
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HVAC Blowing Issues

Why would a central air system triggered by upper level thermostat blow on first level?

Two summers ago we had a new central air outdoor unit installed and it worked just fine until the start of this cooling season.

The house has two levels with one thermostat per level. Recently, whenever the upstairs level calls for cooling the air also blows forcefully downstairs even though the downstairs thermostat is off.

The downstairs blows cool air only when the upstairs thermostat triggers.

I have closed all the vents on the first level and the downstairs is still much cooler than upstairs. Our electric bill is much higher than normal which suggests that the system is working harder than needed due to the recent airflow issue.

Is there anything that would cause a sudden change? As mentioned this airflow issue was not present last summer. Outside of having the furnace cleaned last fall no changes/work has been done to the system.

Thanks in advance for your thoughts.
Old 08-02-18, 05:40 PM
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You need to replace the downstairs motorized zone damper.

If you are very lucky it is only a broken wire. They are usually power closed/ spring open. A broken wire connection would cause the damper to get stuck in the open position. I might see that as the cause 10% of the time. It is usually the damper.

Post some information about your zone control system.

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