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re: frugal ac tips
6 aug 2002
otoh, david writes from arizona:

>>be careful of flowing water continuously on the aluminum fins of the
>>condensor. you will eventually form an oxide of aluminum that is not
>>as thermally conductive as the bare aluminum.
 
>i wouldn't have thought so, unless the oxide is very thick. and maybe
>it doesn't matter, if i continue to trickle water over the fins.

that's what i thought at first. but when i took a small section of
aluminum fin into work and looked at it through a good microscope
you could see the pitting. also, around the copper freon pipe there
were gaps forming between the copper pipe and aluminum fins pressed on.
i guess the water was permitting a galvanic action to occur.

>>my condensor fins took about 3 years to turn black and eventually
>>i lost about 20% of of the condensor's capacity. 
 
>with distilled water? three years is a relatively long time.

with di water. and since we expect our a/c's to last 20 years or more,
3 years is a short time.

>>normally you would use a cooling tower to chill the water
>>and use a water cooled condensor to condense the freon.
 
>maybe this just shifts the oxidation problem to the cooling tower.

it does in a way. the water cooled condensor is usually made of copper,
which is a lot less reactive with water than aluminum. there is an
oxidation problem in the copper also, but is much thicker usually.
there is also a major bio-slime problem with the cooling towers/
water cooled condensors.

>>also please note that if your a/c uses a capillary metering device
>>(not an expansion valve) that if you drop your condensing pressure
>>too low, the suction pressure will also have to drop to maintain
>>cooling capacity. your evaporator could freeze up.
 
>i haven't seen that yet. maybe i need a freezestat...

you might also have an expansion valve which compensates.




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