Return now blowing ice cold air

[bmsemple1]

We have a 3 zone house - upstairs, hall and kitchen thermostats. Recently the upstairs was not getting cool air so we went in the attic and discovered that the damper was sticking. Sprayed DW40 to help it open and close better and problem solved. Now today the large return by the hall is blowing ice cold air (53 degrees) instead of sucking air like normal. I have exhausted a Google search and cannot figure out why the return is now blowing cold air. The only way to stop the air coming out of the return is to turn off the unit completely on all 3 zones. Any thoughts?

 

[u3b3rg33k]

I bet you've got a bypass damper setup and it's dumping out that return somehow.

 

[bmsemple1]

Yes, I’m trying to figure out how and why that’s happening.

 

[u3b3rg33k]

my guess: not enough velocity for the size of the duct to recirculate the cold air, so it falls down and out. beyond that I'd need to see your ductwork setup to guess further.

 

[Milton Shaw]

Look to see if filter is blocked at unit, or that the unit has an air leak in it and is actually getting extra air from somewhere and air balance is way off in the house. In bypass mode, the air bypassed is ducted back to the inlet side of the furnace. That is why I think you have an air leak, normally it would just **** the air back into the unit and not blow out of the return. Check all the damper movement as a stuck damper could be causing the problem, possible since you have already had one stuck.