Is there a way to cap a vent on a rooftop air conditioner?

Question

My a/c unit is on my roof, but when we have heavy rain and wind I get a leak in the ceiling right below where the main ventilation duct enters the house. During a normal "light" rainstorm there is no leakage. So is there any way to cap the main vent of the a/c unit to help keep as much water out of the ventilation without compromising the airflow to the unit? and if there is a way, where would I find the best part for such a repair?

Answer 1

Buy some stuff called MP-1 and seal all around the curb and anywhere that even looks like water could penetrate.I've used that stuff for many many years to make rt units waterproof or rather leakproof.

You buy it at a builders supply store and it comes in an orange caulk tube in many different colors.It is good stuff.It spreads like peanut butter if you wet it and goes on super easy.

But don't block the airflow !

Answer 2

I have found that the panels unless the are put back and taped will suck in water when it rains hard. The indoor fan at certain panels create negative air and will suck in rain water. To see if it is the roof curb shut off the power and take a hose and spray around the equipment hard, flood around it. If no water leaks then put metal tape on the seams of the panels, make sure all screws are in place also.