YSK: If your house has a split AC unit it probably could use a cleaning

I had one installed eight years ago when I bought my house. I’ve used it to heat the entire place, but this winter, I struggled to maintain even 20°C indoors on really cold days.

Well, today I finally brought my air compressor inside and gave the guts of the indoor unit a thorough blasting - and now it feels like an oven in here. I’ve been lowering the thermostat all day, and it’s still way too hot. It literally feels like it’s putting out twice the heat now. I was expecting a slight improvement, but nothing like this.

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This is why HVAC companies tell you that you need to have maintenance performed on them once a year on each system. That’s not an upsell that’s to maintain the warranty as they literally wont run as well year over year without cleaning and will half the life of your expensive system.
- Still feels like an upsell. Just take a hose and spray down the coils and/or vacuum.
  
  Be careful hosing it down or scrubbing it. Those radiator fins are delicate and shouldn't be bent or broken.
  
  I won't say don't do it because I dunno, its probably fine. But watch a how to video or read up on it first. Just don't put a firehose on it.
  
  Don’t. It’s a good way to get mold, and the AC blowing the unhealthy spores around the house.
  Any decent AC maintenance company uses special gear and likely those cleaning foams that minimises this risk.
  
  Hey, it’s your warranty. They do more than just spray down your coils. They’re checking for pressure loss and leaks as well as cleaning the blower motor and wheel (which is where a lot of issues occur).
- I go to an HVAC supplier every year and buy this green can of amazing chemicals. Spray the fins, let sit for about 15min, then spray off with a hose. Gleaming, shiny metal.
I got around to cleaning our outside unit last year, and didn't think it would be a big deal as it looked pretty clean at a glance. Once I got the sheet metal off and started looking and spraying, good lord it was filthy. Now that it is near new again inside, I plan to just take the top off every year and do a regular rinse to keep that buildup down. I can't say how much better it works now from numbers, but it has to exchange heat far more now than before from the sheer gunk I took off.
Those devices absolutely need regular cleaning, because they will get moldy and will spew dirty air everywhere.
Also don't forget to look at your insulation around your lines outside each year. They need replacing sometimes. If you can feel cold, you need a new one. If you don't, you'll see ice forming in the summer, and that is very very bad. Don't forget to test heat and cold BEFORE you really need it (we just tested ours on a decent warm day)

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