I donâÂÂt have all the answers, maybe I donâÂÂt have any. I was just trying to provoke some useful analysis of the problem. The attic and everything up there should be as cold as possible. You mentioned that the new addition has most of the problems and the older attic has none. Might this be because the newer section is too tight and the older one âÂÂbreathesâÂÂ? You should not have to clear snow off the roof with proper roof vents. See link below for roof vents designed for a cold climate. TheyâÂÂre very common here where snow can be quite deep on the roof, I donâÂÂt know if theyâÂÂre common in your region. They always extend above the snow. SR Here is a link that might be useful: 'Maxie Vent'

Float switches are available to mount in the condensate drain pan in the air handler to shut the system down. The switch clamps to the edge of the pan and the small square float hangs over into the pan. If the float rises it shuts down the whole system. An example is below. There are many others. I do not like the ones with the float on an arm. Here is a link that might be useful: Grainger Condensation Pan Switch

It was indeed stolen. The property was bank owned and they had to get it to a habitable state to sell to regular homebuyers so installed a new one. The problem is the contractor installed a brand new air handler, thermostat and condenser onto an existing drain line and lineset. The AC apparently worked while being tested and was then left as a completed job. I bought the house and started the rehab. Straight away it kept cutting out or blowing warm air. It turns out the drain line was clogged which stopped condensation draining so a float switch kept cutting out (this took a couple of visits and a new float switchto figure out). But there also seems to have been a second problem with the line set, as whatever work is done (so far a new float switch, new second condenser, a new second compressor, a new evaporation coil...) it hasn't fixed the problem of the ac running and running and blowing warm air. My question is, am I expected to pay for a new lineset if he installs one as another attempt to fix this 4 month problem? So far it has all been under warranty.

That happened to me. We where getting water on floor so assumed it was coming from our water heater which is right next to the furnace. Water heater guy came out and said not water heater water, water is coming from the pipe from furnace/ac unit drain tube is probably clogged and you just need to clear it. He had been in these types of calls before. So paid him his fee for house call and got to work on pipe/tube. BTW, after it was all said and done when I told my mom what happened she said she uses a air compressor and blows out the tube once a year and pours a little diluted bleach into tube. Wish I had known that. We have been living here in our home for 20+ year and this had not happened before. Tube comes out of the backside of my furnace so luckily it's unfinished basement area. If ever finished I will have to think about a access panel. Keep a big bucket handy because once you pull off tube (mine attached with hose clamp, flexible whiteish kind of clear tube) water will pour out for a bit. After it drained finished with blowing air with air compressor to clear tube, looked to be clogged with algae/gunk. Some chunks came out. If you don't have an air compressor I suppose you could just blow hard on tube a few times ,the one that comes from furnace to wherever it drains. I also held bucket up to where it came from furnace and cleared some gunk with some q-tips and more water came out.