I rent a townhome. It has 2 air conditioning units. I don't know what brand they are. The upstairs does not cool very well. It is always warmer than downstairs.

The return air unit is in the storage closed downstairs. There are 2 return air ducts. The one downstairs was covered up behind the grate with cardboard. The maintenance man said that this duct serves no function. It should be covered up. When I took the cardboard off it pulls air out. He said the return air duct is in the storage closet. This does not make sense to me. What is your advise on this?

Since the lower unit is working fine, perhaps the maintenance man is right. Both units need to freely circulate air. You need a path for air to flow from the upstairs unit through the upstairs and back to the unit. Usually the A/C uses the same ducts as forced air heat. If you can't see how air flows to the upstairs and back, ask the maintenance man. An A/C unit needs air freely flowing to it. An intake in a closed storage room will not work. If you haven't, check the other grates for cardboard.

Whether you rent or purchased the townhouse, you are entitled to a working A/C.

Thanks labman. Is it necessay for each outside unit to have 1 retun air vent each in the house? My understanding is that neither of these return air vents should have anything blocking them, correct?

In general, vents should never be blocked. In some cases, you might block one vent to give better cooling elsewhere on th esame system.