Is it normal for the condensate overflow tubes to blow cool air when is ac is running for central house ac?

Answer 1

The answer in most cases is YES. The reason that the air is coming out of the condensate overflow (drain) tubes is because there is a positive air pressure being exerted by air handler or furnace. There are some systems where there is a negative air draw on the drain and could possibly be capped. Depending on the configuration of the unit and the location of the evaporator coil it could be a normal part of the operation of the condensate overflow to have air coming out. Depending on the way the condensate drain was designed, it may be required to be "open" in order to drain properly. Covering or capping the drain opening could cause it not drain properly or back up. There is no way to know if should be covered or not from a discussion. You would have to see the actual drain design and orientation of the equipment to decide if it should be covered. It was designed and installed that way then leave it alone. Otherwise, a professional should SEE it before making any changes.