Silver Turns Black / A/C Coils Turn Black

My Father in Law has a problem with air quality in his home. The home was built in 2001. He lives in Florida, near the west coast. He has two whole house air conditioner units.
All of his silver, in every room, turns black in a few months. This is not simply normal tarnish. It is very dark (black) tarnish with a powdery substance. As a test, we put clean, tarnish free, silver out in his house and also in a neighbor's house. The silver did not turn black in the neighbor's home (built at the same time, by the same builder etc.) but it did turn black in my in-laws home.
The coils in the A/C units also turn black and leak refrigerant. The A/C units were new Carrier units in 9/2001. We replaced one with a Frigidaire 3/2003. We put a new coil in the remaining Carrier in 5/2004. Both units now need new coils. I have never heard of having to replace A/C coils so often.
He has had the air tested by the local fire department and they couldn't find anything dangerous but I am not so sure. My Mother in law has had a cough for a long time.
Has anyone had a similar experience? Any ideas on the cause and its source?
Any ideas on what tests he might want to have done?
Any suggestions, ideas or thoughts would be appreciated.
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Nope

Gremlins in the ductwork.

Test your jeweler. I think he is giving your gather cheap silver

Get a new jeweler.
Bubba
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Do they use Ionizer type air cleaners in the home? Are they near any high voltage power lines?
Jake
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STLBob wrote:

that and the coils plus neighbor not having the problems would point to something being different. start from setpoint temps, ie. do they maintain house at steady 76-77F and neighbor same? do they use any types of chemicals in the house where it's being sucked into return? cleaners? air fresheners? deodorizers? ionizers?
at one house I recently did a service call they had routinely sprayed Tilex (chlorine bleach) in bathroom which was next to main return and it ate the coil
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