Check the filter first. It sounds too simple, but a filter packed with dust restricts airflow across the evaporator, and a restricted evaporator gets cold enough to freeze. Once there's ice on the coil, the unit blows barely-cool air, drips inside instead of outside, and looks broken. Pull the filter, wash it, let it dry, and give the unit a few hours off to thaw completely before you judge it.
Second, look for ice. If the coil is frosted, that's a symptom, not the disease — it means airflow is restricted or the refrigerant charge is low. Running the unit on fan-only for a few hours clears the ice, and if it returns quickly you have a real fault to diagnose rather than a maintenance issue.
Third, check where the water is going. Air conditioners produce condensate by design, and it's supposed to drain outside. Water on your floor or windowsill usually means the unit isn't tilted correctly in the sleeve, or the drain path inside has clogged with algae and dust. Both are straightforward, and both get worse if ignored.
Fourth, watch what happens at start-up. A unit where the fan runs but the compressor won't kick in, or that trips the breaker the moment it tries, is normally a capacitor or start relay. That's a genuine repair, not a maintenance item, and it's not one to keep resetting the breaker on.
One thing worth saying plainly for older buildings: many pre-war apartments have kitchen and bedroom circuits that simply weren't designed for a large window unit plus a refrigerator. If your breaker trips only when both start together, the appliance may be fine and the circuit may be the real story. We'll tell you when that's what we're seeing.