The drip pan for my HVAC American Standard Unit is full with 6 gallons of water? What is happening?

It's not unusual for a refrigerator to drip a little water on the floor after you replace the water filter-air trapped in the water dispenser system can make the water dispenser drip enough to overflow the drip tray below the dispenser. You can fix it by streaming a gallon or two of water through the dispenser to eliminate the trapped air.
If water drips on the floor from the back of the refrigerator, a leaking water inlet valve or cracked water system tubing could be the cause. A clogged or cracked defrost drain tube could also cause the leak. Defrost condensate water collects in the drain pan at the bottom of the refrigerator so a cracked or overflowing drain pan can also cause water to drip on the floor behind the refrigerator. Check the drain pan for cracks and clean out any foreign objects that may be inside the drain pan.
Excessive frost caused by a leaking door seal can also cause the defrost drain pan to overflow. Check the door gaskets and replace them if damaged.

have your HVAC technician check the pressures in your unit...sounds like you may have low pressure. You should NOT be having any ice build up to melt off.

I think fitting of your shower is not proper. You have to fit it properly if you can or you can call a nearest Plumber to solve your problem.

Copy following links
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#pilot
http://www.thetankatwaterheaterrescue.com/forums/forum3/

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Clean air intake. Change thermocouple.
American Standard appears to be Bradford White or Rheem product from the one image that appears on the AS site.
Air intake located on side of unit funnels air to arrestor screen located under the combustion burner.
Remove burner and blow out screen with compressed air.
If this is Rheem product, then also inspect for broken glass vial that indicates high-temperature FV event, which might also require other parts to be replaced.
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#pilot
http://waterheatertimer.org/How-to-replace-thermocouple.html
http://waterheatertimer.org/How-to-repair-Rheem-TRD.html

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

You have a clogged condensate trap and or line

water drianage is normal, it is supposed to drip from the freezer area to a drip pan under the unit and evaporate before it gets full. check to make sure that the drip pan is properly located and exsits and that you do not have an obstruction hindering the drain opening

Check your condensate drain. It could be plugged. Or perhaps you have a crack in the drain pan.

You can install a condensate drip pan under it and attach a hose to take the water wherever you wish. Drip pans are standard A/C components -- you should be able to get one at an HVAC supply store.