I have a portable dehumidifier in my basement to control the wetness down there. Since I started using it this year, frost continues to build up on the coils. In the past, simply cleaning them off was sufficient to fix the problem. Now, despite efforts with rags, brushes, and liquid cleaners, the problem continues. Short of tossing it (it's 13 years old), any one have other suggestions?

I looked at various online sources, and found the following:

The most common causes of frost build up are:
1. Either the coil is dirty and the unit is not getting sufficient air flow.
2. The unit has developed a leak and the charge is low.

Most of these units are built similar to a residential refrigerator and the units are charged and sealed at the factory, so if the charge is low, it will probably cost more to install valves and service it than to replace it.
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Airflow may be blocked or restricted. Check filters and grating. Also make sure unit has enough clearance from walls and other objects.
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A dehumidifier will often frost up if room temperatures are colder than about 65°F.
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Generally speaking, dehumidifiers have a life expectancy of 8 years.

Thanks for the info. I'm thinking it may be a leak, then. That's to bad; at my age it hurts to take a leak...I mean, as regards the dehumidifier. I'll look over the filter though.