A Bright Red thing Pops out of our Swamp Cooler every now and then. You can push it back in. What is it?

Question

I say it's like a flag, that tells you it needs some sort of service.

Answer 1

You need to change the filter.

Answer 2

It is not the filter you need to change.  It is the evaporative media.  Some newer swamp coolers can compare the outside air pressure to the pressure inside the unit.  If the difference is to high (meaning too much pressure drop across the evaporative media) some sort of warning device is activated.  The evaporative media can get clogged with dirt, leaves, etc.  They are cheap and very easy to replace.

Answer 3

I've been using a swamp cooler for forty years and never had a red flag pop out.  Are you talking about an indoor one?  Is the flag telling you it is time to add water?