This has got to be an air quality issue:

So we have a customer - a moving company - that owns an A/C storage warehouse with eighteen rtu's. Every one of them has refrigerant leaks. Most of the units are about eight years old, but refrigerant is leaking even in units that are 1-2 years old. There is a noticeable accelerated corrosion on the evaporator end plates and drain pans.

We have just received results from water tests we did on the condensate, and the pH is between 4.3 and 4.8. Pretty low, right? Has anybody seen this before? What might cause it?

The only lead I have is that I think they are running propane forklifts inside. Could the exhaust somehow make the condensate acidic?