97 Firebird V6.
Not heater core or evap drain.
Happens when I wet the lower windshield with the garden hose.

Pulled the carpet and padding, discovered leak at the bottom of the heater box.
i'm not sure how the system works, but I'm guessing the water is getting in from the cowl vents at the windshield/hood area.

Is there any known issues with seals leaking? How hard is it to remove the heater box to reseal?

 

nothing?
well, ok.
i'm taking it apart today.

 

Yeah just take it apart and check inside the heater box to see what could be wrong. Post pics.

 

looks like it won't be until Monday.
I will post pics.
it's hard to find info on how the fresh air duct seals to the heater box.

But it definitely leaks from the cowl vent. I poured water strait down the vent holes- most ran out the fender drain, but some streamed out the heater box onto the interior floor.

 

The grommet that seals around the wiring harness that comes through the firewall on the passenger side probably got pulled through the firewall and just needs to be pushed or pulled back into place.

 

the grommet thing is interesting since the wiring harness was removed when the engine was replaced.
I will check that, but the water looks like its coming from the other side of the HVAC box, on the bottom left.
I'll be happy as hell if that's it though.

 

my wife's car had a leak like this it was going under the cowl and into the vent leaking threw the air box and out the blower motor. I could not find it until the blower motor started squeaking when I took it out it was full of water. the cowling seal was warped from heat I guess. replaced it and no more problems.

 

is there a write up on this anywhere?
i just have no idea how the system goes together. add that to the fact that the engine side heater box is very difficult to get to. And the inside part is, of course, under the dash.. just getting started in the right direction is challenging.

 

ok, so i did some work.
removed dash and recovered AC refrigerant.
dropped engine 5 inches and removed HVAC box.
found rust right where the leak was coming from.
now to try and figure it out.

 

looks like the answer is:
evap drain is right above this leak.
evap drain water runs out of the box directly onto the firewall foam seal.
the seal must have stayed wet or just got old and allowed water to sit between the firewall and HVAC box. this turned to rust bubbles which greatly accelerated the leak condition.

all this could have been prevented if the outlet hole dropped down to a short pipe. this would prevent the water from running down the box to contact the seal.

 

gm appearntly didnt learn its lessons from the f-body, my g6 had the exact same issue, after a heavy rain storm i had 3 inches of water on passenger floor. blower motor got destryed and shorted out, 4 bottles of fabreeze and a shop vac later it still smelled the g6 forums were not as tech savy or do it yourself orented as ls1tech so i never got it fixed.