How do you rid your Subaru Legacy 1995 of it's bubbling watery noise from behind the dash when you accelerate and occurs when the heater is on or off?

Answer 1

In my experience, any gurgling noise in the dash area is due to accumulted condensation from air conditioning and from moisture entering through the vents. There is, generally, a drain where the vents and AC condensate void.

1) The drains will, over time, clog; due to dust and debris entering through the vents and critter growth from the moist, dark, warm environment. If you can find a way to access the drain area, usually through the "rear of the hood" vents. You can clear the clogs. This also will rid the car of its musty smell when the air conditioning lights off. Cleaning your vents, periodically, will also help.

2) One way to minimize the accumulation of condensed moisture is to turn off the air conditioning a few minutes before you arrive at your destination. allowing the vent to exhaust the condensate.

That's more than I think I know.

That actually sounds like air trapped in the cooling system. You'll have to bleed the system. There is a bleed screw on top of the radiator on the opposite side from the fill cap (passenger side). Open the bleed screw and fill the radiator thru the cap/neck with the engine off. When coolant runs out of the bleed screw, its full.