condensate --> ice on air conditioning evaporator coil?

Our home central A/C has developed a problem recently - water sometimes drips out of the ducting surrounding the evaporator coil at a high rate. Cooling in the home seems to be diminished as well.
This condition is sporadic, and we never had the problem in years past. I've also heard sporadic banging sounds coming from inside the duct from this area.
Today I formed the hypothesis that condensate is freezing on the evaporator, blocking airflow. The banging could be ice falling off the evaporator, and the fairly significant water could be the ice melting.
Does this sound like a plausible/likely explanation? What other things might cause this problem? What ultimately is the cause. And what should I do about it?
Part of my hypothesis is that after several years of drought and dry weather (here in sodden Maryland), this year's rainfall has meant high humidity and hence more condensate than in the past.
Could it also be that grime/dust has built up on the heat fins in the evaporator? Is opening up the ducts and cleaning these something reasonable to think about doing, or does build up usually signal the need for a new evaporator/heat exchanger? Is cleaning practical without specialized tools?
What about insufficient airflow through the ducts - would this increase condensation and lead to ice formation (which would further restrict airflow)? If I increase the airflow (by opening all vents wide open), is the problem likely to go away?
Thanks.
Bill Christens-Barry
--
Wm A Christens-Barry, PhD
Equipoise Imaging, LLC
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Hey Doc, you got a feather in your cap and you earned it, but I believe your trying to diagnose something out of your league.
The most sensible action to take at this point, is to call a HVAC company.
The noise you hear, could be gremlins, so hurry!
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We had the same problem about a month ago. We were low on freon. Guy came, added freon and no more problems.
On Wed, 2 Jul 2003 20:36:23 -0700, "CBHvac"

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Did he check for leaks? That Freon went someplace.
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Hi Who, hope you are having a nice day
On 04-Jul-03 At About 07:47:58, Who Cares wrote to All Subject: Re: condensate --> ice on air conditioning evaporator coil?
WC> We had the same problem about a month ago. We were low on freon. WC> Guy came, added freon and no more problems.
I hope he did a leak test and repaired the leak first.
-=> HvacTech2 <=-
.. "I can levitate birds but nobody cares..." - s.w.
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