Zoning Bypass Duct - How does it know when to close?

[l_kent_a]

I have a 3 zone system in my house. When one zone is working, air flow is really good. When the next two zones turn on, air flow drops dramatically and if all three zones are open, there isn't sufficient air flow to cool all zones.

Here's what I think. When only one zone is open, the damper in the bypass duct opens because of excessive air pressure. But, when the other two zones turn on, it may take a while for the bypass damper to close. Therefore, a lot of cool air is circulating in the AC unit rather than through my house.

When the zoning was originally installed, there was a counter weight on the bypass damper. However, the service tech removed it several days after installation saying that we didn't need it.

I believe that because there's no counter weight, it may take time for the bypass damper to close when all zones are running, therefore, air flow is deminished.

Does this make sense or am I full of s*?

[jrise]

It's the counterweight that opposes the air pressure in the bypass duct and closes the bypass when no pressure is present. Without the counterweights the bypass will be open whenever there is pressure in the bypass duct. Which is the path of least resistance for the air whenever the blower operates. Try manually closing the bypass damper. Mover the handle (that use to hold the weights) to a position perpendicular to the bypass duct. Use duct tape to keep it in this position if necessary. Then turn the fan switch at the thermostat fron AUTO to ON and see if that improves your air flow.

[dash]

Originally posted by l_kent_a
I have a 3 zone system in my house. When one zone is working, air flow is really good. When the next two zones turn on, air flow drops dramatically and if all three zones are open, there isn't sufficient air flow to cool all zones.

Here's what I think. When only one zone is open, the damper in the bypass duct opens because of excessive air pressure. But, when the other two zones turn on, it may take a while for the bypass damper to close. Therefore, a lot of cool air is circulating in the AC unit rather than through my house.

When the zoning was originally installed, there was a counter weight on the bypass damper. However, the service tech removed it several days after installation saying that we didn't need it.

I believe that because there's no counter weight, it may take time for the bypass damper to close when all zones are running, therefore, air flow is deminished.

Does this make sense or am I full of s*?

You're hired!!Call that tech tell him"you are the weakest link,Good Bye!!

Bypass dampers are oftened sized too large,if so it is difficult to get them to work correctly with the weights.

Tell us the tonnage,damper and bypass sizes.to see if they are close to what they should be.

[l_kent_a]

Thanks for the feedback.

I'll try closing the bypass duct this weekend.

By the way, I have a variable speed fan unit so maybe the fan unit will be smart enough to slow down if there's too much pressure.

[jrise]

It works the other way around. As the pressure increases, the blower will speed up to overcome the increase. So if your bypass is open, then the blower doesn't see any pressure to overcome because all of the air is bypassing. Also check your circuit board on the blower. Often there is a DIP switch that must be set to let the blower know that there are zones that will vary the system resistance from time to time.

[beenthere]

You need the weight, and never let that tech touch it again.

[dash]

kent,

Was that "prodiyer" that was out there??

[dan sw fl]

Originally posted by l_kent_a
When the zoning was originally installed, there was a counter weight on the bypass damper. However, the service tech removed it several days after installation saying that we didn't need it.

That SORRY little service tech KNOWS about sabotage,
but not by-pass function.

QUITE SIMPLY:
Restore the weights to the by-pass damper.

[duc dowg]

he dont know much about zones.

[bldgcode1]

Apparently the tech didn't know how a barametric damper operates. If the counter weight isn't there, the damper is "blowing in the wind."