This website is pretty helpful in repair tips. I agree it is likely a clogged drain line - you may try to find where it is supposed to drain into the pain and work backwards Here is a link that might be useful: appliance repair forum

I would recommend using larger 3/4" PVC pipe for drain piping. the larger diameter will reduce the frequency of clogging. They do make condensate pan tablets that get placed inside the a/c unit and reduces mold and slime growth in the drain line. Check with your a/c repairman to get the tablets if HD does not carry them

That is not according to code. If that standpipe backs up there will be cross contamination between the sewer line and the softener. In many locales softener installs must be done by a licensed plumber. Is you installer a licensed plumber? I ask because he obviously does not know what an air gap to drain is The softener drain line must have an air gap to the drain. The way it is configured, If he had simply run the drain line up a couple inches then 90's it and 90'd it again so the line was in fee air above the standpipe he'd have had an air gap. Call him back and make him do it according to code or make him buy a nifty air gap from www.airgap.com.

I thought we agreed that we were not going to limit the discussion to the climate of Katy Texas? Well the OP who started this thread made it sound like he lived near me... which would mean using my climate numbers as opposed to somewhere else. I don't service areas outside my climate so why on earth would I entertain this idea of yours? (I offer advice on occasion but that is all it is --- professional advice --- as this is what I do for a living, I don't sit all day in forum board --- I do have a life outside of HVAC, what little it is right now it's still a life...) You again trying to fit HVAC in a confined specific box in which it does not fit. What are the odds that someone will find that information useful? Probably close to 0% if I had to guess. That sounds like a waste of time... I know this seems productive to you so knock yourself out if you want to do that. Exact numbers are not necessary to educate everyone the source of the condensate. Then why not use the 'about 0.8 gallons estimate' and run with it? An air conditioner in my climate can produce upwards of 5 gallons of water an hour. A condensing furnace will not produce that much. An 80% non condensing furnace will produce 0 condensate water. Oh so let's use the AC condensate line for the furnace condensate. Problem solved right? Most likely not. Drain systems are complex especially when you throw in the variable that a condensing furnace imposes. See I've led your hand to this point --- where the concern right now up to this point is how much more condensate a condensing furnace will produce in my climate Katy, Texas versus other less humid climates in which those furnaces are installed typically in a basement. You don't have the over head flood threat you do here in my climate. All of this --- except: there are safeties on that condensing furnace that if you don't do it properly, the furnace will shut off on nuisance trips. So the furnace is not likely to be the cave in threat due to condensation production. They tend to leak water in drips around the furnace while having very erratic operation most often. You don't get these kinds of problems with a 80% non condensing furnace. What a home owner knows versus that of a pro... you think condensate is the only problem you have to contend with. What is your definition of making this actually work? How does the condensing furnace then become the ceiling cave in threat? Changes to the condensate drain system by people who don't know what they are doing. It may be a home owner, land lord or even a technician who doesn't understand the implications of what they are doing. How much water one produces whether here in this climate in Katy, Texas or a less humid climate (in winter) like Chicago / Wisconsin --- the different in condensate production doesn't matter... *IF* the system to get rid of condensate is adequate. This thread was about a young guy presumably in his 20's attempting to install a condensing furnace in a probable high humid climate. That condensing furnace was bought used. Who in their right mind sells a condensing furnace (used) in a probable high humid climate? One that tried to install said furnace and couldn't get it to work. I have an innate ability to read between the lines. I've seen quite a bit of 'Tom Foolery' in my nearly 26 years of doing this for a living. We can't get it to work so we'll take it out and sell it to someone else. So what makes the condensate drain system of a condensing furnace adequate? The right way. What is the right way? The opposite of wrong. If you want to learn how to do it: There are trade schools for that. Class dismissed......