A/C condensor freezing up

Here in FL, my centeral A/C condensor coils freeze up after running for an hour or so.I haad a repair man check it and found the freeon was Ok, but said the Evaporator coil was dirty and should be cleaned. He also said the system didn't have enough return duct area. The house is at least 25 years old and the current a/c unit is 9.5 years old. It was working fine with the duct work it has, up until this problem. The repair man cleaned the coils and I still have the same problem.
Not sure if I want to let him start installing a new duct. Any suggestions? He is coming back this morning . Thanks
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A near ten-year-old system may not have enough evaporator _fins_ remaining to be effective any more. That, and the swaging between fins and coil is probably so corroded that there's poor thermal conductivity fin-to-coil.
If your return was undersized to begin with but everything else was healthy, it might work OK. But, enter corrosion of the evap, some crud that cannot effectively be washed out, some reduction of the size and number of fins by un-judicious use of corrosive "Coil-Brite" type cleaners, a tired, crudded up indoor fan, ducting so linted up inside that it's like a fur blanket, the inevitable leaks in ducting, etc...and.... you're ready for a new system.
I don't know where you live, but if you have sulfurous water in your home or even nearby, the H2S gas makes the corrosion problem even worse.
Maybe its not what you wanted hear, but nothing lasts forever. On the bright side, you'll probably enjoy the energy savings you'll get from a decent new system. Don't just throw it in, though. Let the tech repair all your ducting, fix leaks, replace flex duct; it can be hard and crispy, and on the verge of failing, and the new flex has over twice the R-value of the old material. It won't be cheap, but it's really worth it.
LLoyd
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Fins wrote:

The outdoor condenser coils are freezing up, - or is it the indoor evaporator coil freezing up. Is this a Heat Pump?
Many years ago, I found a strainer in several old GE condensers that had plugged. The techs, not knowing how to troubleshoot, would go out and overcharge them loading the condenser full of liquid. The condenser coils were aluminum however, there was copper on both sides of the strainer. I immediately diagnosed the problem, and back then, blew the overcharge and removed the plugged strainers. Removed all dryers, purged the system, installed new filter-dryers, evacuated the systems and recharged them. They performed to specs. He may be correct concerning the Return Air duct, which should improve system efficiency. Do some reading/learning & examine the ductwork for leaks and proper sizing. http://www.udarrell.com/proper_cfm_btuh_duct_sizing_air_conditioning_systems.html
- udarrell
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