[danans]

> I'd think that a fixed amount of air compressed in the compressor means a fixed amount of condensation runoff from the unit

It's not compressing air (like in a car tire). It's compressing a refrigerant. That refrigerant goes through phase changes (liquid to gas).

One major issue is that for most ACs, the compressor is cycled on and off according to the target temperature (via a thermostat, usually at a single location), not humidity. That means humidity can rise without the AC kicking on to bring it down. Remember in most typical houses, temperature and humidity are not very uniformly distributed.

Furthermore, if the humidity rises high enough before the AC kicks on, and then the AC kicks on at high power, you can get sudden localized cooling and then condensation of humidity to liquid water inside the building, which leads to other problems, especially if it happens behind the walls.