OK, first for pouring beach in, its much easier to add a tablet twice a year...
Amazon.com: OUTLAND ENGINEERING AC-912 A/C PAN CLEANER TABLETS: Health & Personal Care bleach stops working as soon as it is rinsed out, I make my own tablets by breaking them pool tablets into pieces, the arm and hammer breaks easiest, but I use a bunch of them in a bunch of houses, so for $6 the outland tabs are good for a single person, unless you have a pool and already have the tablets, break a piece of throw it in there...
Next- Phillip is that pan under the unit filling with water?
I would have never installed it that way, first off there looks to be no float switch in the pan, this is a little switch I linked you to earlier, when the pan fills the switch shuts the unit off... This is code around here...
next- there is no drain on the pan, I would install a drain in the pan, drill a hole in it put a bulkhead fitting {home depot sells them, its a fitting that lets you tighten it into a pan, they have them for the pans that go under water heaters and washing machines}, plumb that into a second drain line {you can do it smaller if you like instead of 3/5 you can do 1/2"} this will be a safety in case the drain pan fills, and I would put an alarm {like I linked you to earlier} in the pan so you know when its wet.. You will hear it because the duct work will work like a horn and blast it through your house...
Fixing drywall is easy, getting rid of mold is not.. them 90's are probably causing all of your trouble, I would have put the tee vent where that first 90 pointing down is and then used 2 45's to get under the unit, 2 90s back to back like that is not a great idea for flow... with the vent rite at the first 90 is would fast drop into the 2 45's and kept moving fast down to your sink... Which is another issue, is this just draining into a sink or is it plumbed into the plumbing?
Was that unit professionally installed? Judging by the flexi stove gas line 3"s from you B-vent exhaust, the tape riddled insulation on your suction line, lack of service switch and or firomatic safety {unless its on the ceiling I can't see}, and the unprotected and non secured romex powering the unit, I would imagine a home owner before you did this himself....
