Because if it ices over, your furnace will stop working on the day1 you most needed it.
Flushing it out from the outside with a bucket of hot water and a pump similar to this one 2 will melt the ice and open up the drain and you will get heat again.
1 Day because if your freezing weather lasts much longer than that, your homebuilder probably engineered a house that could handle the cold. Unfortunately my house was built by southern rednecks who’d never heard of insulation.
2 Not an endorsement of any brand or retailer. Just make sure it has a long enough hose. That’s what made it work better than some of the things I tried first.
Maybe you should build an outhouse. That should make your home less shitty.
For real though, fixing these sorts of things can make you wonder why you didn’t know of it earlier, especially if it’s so important! My air conditioner was able to keep the house cold, but was running a lot. My wife called a guy to take a look which kinda pissed me odd because it made me feel like I can’t fix my own shit, and it’s still working and this will just waste money.
Turns out the coolant was very low in the air conditioning unit and it needed to be recharged. Had no idea this could happen. Afterwards the air conditioner ran for a couple of hours a day instead of running for most of the day and night. Saved us a lot of money in energy costs and I got a bit of a lesson about pride in my home repair abilities. Sometimes it’s ok to call someone.
for what it’s worth, coolant is not consumed by an air conditioner – the same initial charge can last 20+ years. Low coolant either means a leak, which the technician should have investigated and fixed or ruled out, or improper initial installation.