Wonder what this is.
A clogged evap coil!
Dominic…you da man!!! 
You should be an inspector. 
lol
That TPRV needs to be plumbed correctly! Or am I missing something? :mrgreen: 
Bet the realtor asked you if the drop was good, didnt he?
Looks like some pretty suspicious biolological growth. Is that a parge coated wall surface to the left of the picture with some spray foam in the corners? A location and condition would really be helpful to take a nice stab at it.