I own a late 90's double wide trailer house, manufactured in the USA. The furnace is a 6 year old forced-air, natural gas and does not have a humidifier. The house has been unoccupied for about 6 months while the AC was set to on, at about 75°F, for the whole summer.
The pan at the bottom of the furnace has a line that is connected to a drain pipe with a 'Y' fitting that has been sized down to clamp the smaller line to it. It looks like they tried to form a P-trap in the small flex tube by making a U bend, held by a zip tie. The drain line is also for the washing machine just before the 'Y' connection.
I found that the flex duct that connects the furnace to the duct work on the opposite side of the house is full of water and collapsing from the weight.
After I check the flex drain line to see if it is plugged-up, how can I tell if this is condensate in the duct or could it have backed up from the drain? This looks like a poor design how can I improve it or is it okay as is?