The most common failure mode is for the fan shaft to seize up with crud. Start by freeing, cleaning and lubricating it.
I've gotten several "free" dehumidifiers that way. At my local dump they're set aside with the refrigerators and window air conditioners so they can recycle the refrigerant before they get put in with the scrap metal.
If the fan's not turning, the unit freezes up and stops producing water, so folks just toss them. I'll grab a couple that don't look too old or beat up. About 75% of the time, I do what Doug says: give the machine basic maintenance and they're good to go again. I use them in my rental properties and they've run for years after being "resurrected."
Clean the dust outta the coil and oil the fan motor every couple years. Of course, newer models are more efficient and may save me a few bucks a month off my electric bill; but that savings will take a long time to offset the cost of new unit.
'15, F250 XLT, CC, 172", 6.2L, Ruby Red, FX4, 3.73 Locker, ESOF, Rear sway bar, Chrome, Back-Up Camera, Tail Gate Step, Upfitter Switches, Ford Mud Flaps & wheelwell liners, Trailer Brake Controller, White-Night Backup Lights, Husky Liners, Line-X Bed Liner, Master Lock Bed Lock, Swing Case tool box, AnchorTrax Cargo Control System, Audio by Alpine & Audio Control, Audiovox Remote Start & Tracking system, Fumoto Valve, BAK-FLIP HD cover. Hella Driving Lights, LED Cab-Step lights, LED Bed Lights. Putco LED Daytime Running Lights
~~~(RIP. Retired by a big tree limb during Hurricane Irene.)~~~
'01 F350 XLT, CC, 4x4, V10, SRW, LWB, Auto, 3.73LS, Island Blue