So,

You have grossly increased the heat load and are now asking why the units doesn't cope.....

Each of your refrigeration units have been carefully designed to cope with the enclosed space within the container it serves.
Any alterations to this space, like draughts or increased volume, will affect the refrigeration units.
i.e. they will not cope.

The only solution to your problem would be to get someone to design replacement/additional plant to serve your new chilled area.