Bypass Damper Leakage

[ferd42]

I have a Carrier FB4C036 operating at 0.26" SP supply and 0.24" SP return, speed tap 5. Carrier's Airflow Performance chart indicates 1,176 CFM at 0.5". Measuring supply registers with all zones calling and bypass damper closed yields 920 CFM. Bypass damper is a PRD 12x8. Could there be significant (200 or 250 CFM) leakage around the closed bypass damper? If so, what should I do to increase flow to the conditioned space?

[Pcyrana]

There will me some leakage past that bypass damper, as there is with all dampers.
Whether it will be 200-250 CFM, I would not be able to determine exactly.
Did you take an airflow reading after the bypass damper?
With the by pass damper completely closed, what position is the arm in?

[ferd42]

The damper arm was on a 45 degree angle, down and in the direction of flow. Closed with all three zones calling, slightly open with one or two zones calling. I think it's working.

Someone on HVAC Talk suggested traverses, but I'm in Mexico and won't be back at the job (in DE) until mid-June. At which point I'll do a traverse and use a duct camera to inspect the damper blade.

Thanks for your help!