My ac is leaking on the floor. - 2003 Chevrolet Suburban 1500

this will be condensate from the fins of the ac evaporator in the car and is leaking onto the floor because the drain on the unit is blocked either in the hose or at the bottom of the ac box

The rubber plug will be to drain out any water that is under the carpet and so prevent the floor from rusting out. As to water getting there check out the heater core /hoses for leaks and check out the AC drain hose for blockages and ac condensate overflowing out of the box and onto the floor.

ac drain pipes are on the passenger side front floor area (just about where your feet go) under car when cars heater core gets a hole in it lots of times antifreeze will leak inside car on floor try to get a small sample of fluid thats leaking out with a tissue or something (white In color) see what color fluid is ,see if fluid is slippery like oil or not (rub it between fingers)
Antifreeze= orange or green in color
Transmission oil = red or brown
motor oil = brown to black
washer fluid = Blue or drk orange
ac condesate= clear water (cold)

I think you want to say AC evaporator leaking on floor
the drain tube could be plug

If you are getting clear water on the floor, check the ac drain on the outside of the firewall near the passenger floor.

I just bought my car and front seat floor boards were getting full of water took it back and the cause is Ac water line under dash was not connected and dumping water in dash and on floor

Ac hose leak?
leaking heater core?

Hint: it leaks when it RAINS

If it were related to the heater core or the AC drain, it would be leaking when it is not raining also, so those diagnoses are not logical.

The grand prix has a long history of floor leaks from seal failures around the air intake under the windshield cowling, where RAIN water runs in.

It is possible that the ac drain is clogged blowing some compressed air can clear it and allow water to flow again it is also possible the ac box may be leaking

When you open car in morning is there a strange smell in it? You can check ac pressure with a tyre gauge should have a filler looks like a tyre valve near ac unit under bonnet check if it has pressure if not you have a leak and need to find and fix that befor regas. If leak suspected (you got not preasure in unit) get ac regasser out and tell him/her you think it maybe leaking and if passenger floor wet and your system still uses freon good chance you have a leak, they should dye the gas and the leak will become very obvious very fast once car started and ac turned on. But if you use freon you may not be able to regas depending on the laws in your neck of the woods. Here in australia if your useing freon and you need to regas you have to change a fair bit to use a legal gas which depends on type of refrigerant unit installed.

did you replace windshield?
do you have a sunroof?
these are the only places water could leak.
it could also be the condensation from the dehumidifier of the AC. maybe they forgot to reconnect the hose to expell the water.