Have a single 2.5 ton a/h v/s and a 2 ton compressor.

The fan speed is set at 350 cfm per ton or 700 cfm total.

This is a 1 1/2 storey house w/ 1,000 s/f down & 600 s/f up stairs.(Spray Foam Insulation)

To cool the upstairs, I have to all but close every supply duct damper that feeds the 1st. floor.---> 10 ea. 6" rigid pipe....( as a side note there are 3 ea. 8" return ducts on the 1st floor.)

Supply ducts feeding the upstairs (dampers wide open) are as follows--->2ea. 8" rigid pipe, approx. 40' in length...and approx. 5 ea. 90 degree fittings on each duct.......also 1ea. 6" rigid pipe going upstairs.

Upstairs there is 1ea. 10" return main trunk w/ 2ea. 8" pipe splitting off the main pulling air from the 2 bedrooms.

With dampers positioned as they are, I get a 3 degree differential between up & downstairs

My question is....With a educated guess (without doing a s/p test)with the 1st floor duct dampers being closed approx. 85 to 90% will this harm the system?

thanks for any imformative response...