A/C in rear yard

We're trying to figure out if it's legal in NYC to have A/C condensers in a private back yard of a walk-up apartment building, and unfortunately we're getting conflicting opinions on this. One architect cited NYC ZR 23-44 which allows A/C condensers but the text indicates only for single and two-family residences. Then another cited the NY multiple dwelling law which does not list A/C condensers (and thus disallowing them), but Section 25 states that it only applies to buildings erected after 1929, and in this case the building is older. Does anyone have direct experience with this, or know of architects/contractors that have dealt with this issue before? Any help will be appreciated. Thanks!