Why does my portable AC shut off every 90 minutes with an FL code?

Elevating the unit is a common workaround for these cheaper portable models and it won't hurt the motor or compressor one bit. The reason you're hitting that "FL" code so fast is becuase the internal evaporation system can't keep up with the humidity in your room. Most of these units use a "slinger" fan to throw water against the hot coils to turn it into vapor and blow it out the exhaust, but in high-humidity areas, the tank fills up way faster than it can evaporate. As long as the platform you've built is stable and level, you aren't losing any performance. The internal components don't care about thier height relative to the floor. If anything, you're actually saving the internal parts from potential corrosion by keeping the water level low. The fact that the upper drain isn't working for you is normal; that port usually only captures moisture from the top evaporator coils, while the bottom port drains the main reservoir where all the "overflow" goes. If you want a more permanent fix than a tray on the floor, look into a **condensate pump**. You can find small ones for under $100 that sit right on the floor. You run the hose from your bottom drain into the pump's reservoir, and it will automatically pump the water through a small tube into a sink or even out the window next to your exhaust. It beats having to empty a tray every hour and makes the whole setup much more set-it-and-forget-it. Just make sure your exhaust hose is still as short and straight as possible. Sometimes when people raise the unit, they end up stretching the hose or adding weird bends to reach the window. That creates backpressure and makes the AC work harder, which can eventually shorten the life of the compressor. Keep that exhaust path clear and you'll be fine with the platform setup.

I had this exact same issue with my unit last summer. Elevating it works, but I skipped the tiny tray and went straight for a 5-gallon bucket. I just used a length of 5/8" clear vinyl tubing from the hardware store and secured it to the bottom plug with a hose clamp. Those flimsy hoses they give you always kink and cause backups.

One thing that helped me cut down on the water was sealing the window kit better with some weather stripping. If humid outside air is leaking in, you’re basicly trying to dehumidify the whole neighborhood. once I taped up the gaps, the tank filled up way slower.

Check your tilt. If the unit's leaning even a tiny bit away from the drain, it'll trip that sensor way too early. I had to shove a couple shims under the front of mine 'cause my old apartment floor was crooked. Made a huge difference in how long it ran.

Also, keep an eye on the rubber stopper inside the port. If it’s gunked up with slime, it messes with the flow. If you're still drowning in water, you're probly pulling in way too much outside air. Check if your bathroom or kitchen exhaust fans are running and sucking in humid air trough the cracks.