Louis that water billing for the entire building is condensed into one.

As long as the condenser, compressor and evaporator still work with no major leaks.

First you need to talk to the seller about getting an HVAC Tech, or handyman, to close the service valves on the condenser, with an allen wrench or service tool, so that moisture, non condensibles and bugs don’t enter the unit.How close is the unit to the house?

The wall system needs to be able to remain dry and the fear of covering old siding is that you will trap condensation between the existing vapor barrier under the old siding and the new vapor barrier you would put on top of the old siding, causing internal rot in the old siding. 

2 days later after being fixed we have another break in most likely from the same guys this time taking the AC condensers from the basement!

One piece of advice if you do end up putting a unit or two in....chain the condenser down to a concrete pad or put a locking cage over it.

The first facility I bought rained INSIDE the building;)  I didn't know that a non climate controlled facility should still have insulation to prevent condensation. 

Now, the lady called me later in the day and is claiming that the water is coming from my unit . she says its from the condensate mechanical closet.

It could be a plugged drain line on the condenser.

We just replaced a 25 yr old A/C condenser that we nursed for several years.