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.