Hi, I have a H3 Hummer 2008.
When I start it up, begin moving forward, or quickly decelerate I can hear a lot of water moving from one place to another under the dash or maybe just behind the firewall.
I think that my AC Drain Line y Clogged but I cant find the Line.

 

Do you have a moonroof?
The drains are known to become clogged and trap water.
Are the door's drain holes open?

 

I unclogged the drain lines of the sunroof but in the dash still a lot of water.
A day ago I sent the H3 to a car wash, I think water enters to the dash because the drains are clogged.
Door drain ?

 

The is no place "in the dash" to hold water, but the HVAC box is in front of that. Check your coolant.

Otherwise, it is your sunroof, and there is a set of front and rear drains that need more than unclogging, they need the sunroof drain fix per the thread here and vids per Google search.

 

When I start the AC sounds like air is making bubbles in the water.

 

When I start the AC sounds like air is making bubbles in the water

 

Sounds like the drain opening for your A/C evaporator is plugged (you know, the puddles you always see under the vehicle when the A/C is on and you're at a stand still), and the housing has filled with condensation water. That's why you're hearing sloshing, and when the blower is on it's blowing bubbles.

 

How I fix it ?

 

By looking it up on Google would be a start. The drain comes out of the firewall on the passenger side under where the AC lines go into the HVAC exchange box.