Thoughts on DIY 3-hose mods for small portable ACs?

I did somethig similar with an old Whynter single-hose unit a few summers back. I used 5-inch dryer venting and alot of HVAC foil tape because Gorilla tape acutally started peeling off once the unit got hot. One thing I found is that even if you cover the exterior grates, these cheap portable units have huge gaps around the internal plastic frame where the blower sits. I used a stick of incense to trace the airflow and realized it was still pulling a ton of air from the room through the bottom of the casing.

If you're worried about the door seal, ditch the towels. I went to the store and grabbed a sheet of 1-inch R-Tech rigid foam insulation. You can cut it with a simple utility knife to fit the sliding door track perfectly. It’s way better at blocking the heat than towels and it stays put without needing screws or wood. It looks a bit like a science project, but it stopped my compressor from cycling every five minutes.

The three-hose setup is defintely better than the negative pressure of a single hose, but don't stress about making it 100% airtight. As long as you're getting most of that condenser air from outside, you've already won half the battle against that vacuum effect.

I think you're overcomplicating things with the three-hose setup. I tried a similar rig with my Midea unit last year, and while it stopped the negative pressure from pulling in hall air, the compressor started cycling off every fifteen minutes. These small motors aren't designed to pull air thru long runs of flexible metallic ducting. The static pressure is likely way higher than the internal fan can handle, wich ends up overheating the coils and potentially shortening the life of the machine.

Instead of adding more hoses, I found much better results by just insulating the main exhaust hose with a Reflectix wrap. If you’re worried about the unit sucking out cooled air, just crack a window in a far-off room like the bathroom or kitchen. It’s better to let a little unconditioned air in through a controlled gap than to starve the condenser and burn out your unit. For the sliding door, I just used high-density foam strips—they’re cheap, require no tools, and seal much better than stuffed towels.

Totally agree on the foam board, it's a game changer for the seal. One detail that often gets missed with these DIY multi-hose rigs is the heat soak from the intake ducts themselves. Since you're pulling hot outdoor air thru that thin metallic ducting, those hoses basially turn into space heaters inside your room before the air even reaches the AC. I'd suggest wrapping the intake lines in some cheap reflective bubble insulation. It prevents the heat from radiating back into the apartment while the air is in transit to the unit.

Check your compressor temps. If you're running a Midea Duo or even a hacked LG LP0817WSR, those three hoses are likely creating way too much static pressure for the condenser fan. I’ve seen guys burn out thier capacitors beacuse the airflow CFM dropped below 200. If you realy want to optimize, swap that flimsy dryer ducting for 6-inch semi-rigid aluminum. It has a smoother internal bore and doesn't collapse under suction. Also, check the drain pan—if you're pulling in humid outside air thru those extra hoses, you're going to be emptying that condensate tank every two hours unless you set up a continuous gravity drain.

Reminds me of the early 80s when we'd rig up window units into van conversions with nothing but a jigsaw and some heavy-duty weatherstripping. Most of these modern plastic portables are built like toys compared to the old steel-case Frigidaires, so don't be surprised if the plastic cracks when you're wrestling with it. If you're worried about the seal, try some 'roped caulk' around the hose inlets. It’s what we used to use for winterizing drafty Victorian windows back in the day. It stays pliable, doesn't ruin the finish like Gorilla tape, and you can pull it right off when the season ends. Just make sure you aren't kinking those hoses or you'll toast the compressor.

Have you ruled out that you're actually losing more cooling via the 'hacked' intake than you're gaining? I've seen a few of these three-hose setups where the added surface area of that uninsulated metallic ducting acts like a radiator, dumping heat right back into the room. Before you commit to this, have you checked if your unit's internal fan is even strong enough to overcome the friction in those extra lines? You might just be choking the condenser and causing the compressor to run hotter than it should, wich kills the lifespan of the unit.