Where is the A/C evaporator drain line located?

Is the evaporator freezing? Clearly the evaporator does sweat and that will run out the drain but if you have enough water that you are hearing it move then I suspect you have a greater issue then just a drainage issue.

If the drain line is clear then this should handle all water that collects in the housing.

I would suggest we start with checking the pressure on the system and make sure that we don't have a freezing and thawing of the evaporator.

Here is a guide that will help with this:

https://www.2carpros.com/articles/re-charge-an-air-conditioner-system

When you verified the firewall drain is clear, did you find that there is water coming out at all?

Basically if the water that you are hearing is in the housing then it should come out of this drain so I am thinking it is plugged inside the housing.

However, if it is not then we need to go back to the pressures.

If we solve the possible ice issue then the drain will be able to handle any normal condensation.

Below is a chart that will help with pressures so let's run through this and go from there.

Thanks

Hi, I'm Dan. The drain for the A/C on that car is very short and goes right through the firewall. However, there is a Technical Bulletin from Ford about rainwater getting into the A/C system from the cowl area at the base of the windshield. Ford wants you to remove the cowl, and add liberal amounts of silicone sealer in this area after removing the foam. I've attached Ford TSB # TSB 14-0157 to this reply.

I've also attached a picture of the A/C evaporator case (upside down).

And the procedure to remove the cowl.
Let us know what you find.