I had a problem with my AC units. I thought it was the freon which was too low.
CY: yeah, everyone says that.
The AC guy came out and said that he first recommended cleaning the outside AC units, at $80/unit. His partner says that my units look clean. He says that they should be cleaned every year. So he takes off the top casing, washes it with a lawn hose, sprays on an A/C cleaner (sodium hydroxide based), and washes it off.
CY: Hope he left the cleaner on long enough to foam up. I've worked on plenty of units that "look clean" but aren't. You have to get the system running, and check some temperatures to find out if the coils need cleaning.
$300 later, he says that the freon needs to be added too. Ok, another $150 later the problem is solved.
CY: Hope he left the system running long enough to dry out, afterwards. The evaporative cooling can throw the numbers and pressures and temperatures around a bit.
I got the feeling I was hood winked and robbed.
CY: I can imagine that.
Two questions. Is washing and cleaning the units standard practice?
CY: Yes, it is.
Is it even necessary to do it once a year?
CY: Depends how much dirt and dust they pick up. I think that most cases, every 3 to 5 years is good.
On my old house, I haven't cleaned them in 3 years and never noticed a higher than average bill for not doing so.
CY: Well, if you take the energy bill from three dirty-coil years of use, they will be about the same. Clean the coils, and the energy bill should go down.
How much efficiency is lost by not cleaning the units?
CY: I've seen 100% loss of efficiency in units that were dirty, but looked clean. I worked on one that was simply not cooling the house at all. After cleaning, it worked great. The home owner was talking about replacement, but was willing to let me clean it and see if that helped. It did.
The repair guy quoted 50%, but I made a smart ass remark like 5%/yr.
CY: The repair guy was a lot too low.