I noticed a large discolored area around the drain pipe outside the house for the condensation pan. It looked like rust. I got out the ladder and climbed up in the attic to inspect the two units. One was fine and the other has rust inside the bottom of the pan. I cannot tell if the rust is from the pan (nothing obvious) or if rusty water is draining into the pan. There was no standing water at the time of inspection, but then the A/C units had not run since last night.
The drain pipes for both pans connect to the side of the pans, not the bottom. This allows a small amount of standing water to remain in the pan until it evaporates away. It seems to me a better design would be to have the drain on the bottom of the pan at the lowest point so there would never be any standing water.
I am looking for suggestions of whether this pan should be replaced (6 years old) or if I should just keep an eye on it.