Q: Water leak on the passenger floorboard w/defroster and AC running.

asked by on October 30, 2016

When running defroster on max hot settings (outside air and AC on), there is a high pressure noise followed by clear water leaking into the passenger floor board. It does this after 30 minutes of driving with defrost, and usually immediately stopping at an upward incline coming off the freeway. In a heavy rain climate.

the water is clear and odorless. Heater produces hot air and defroster works with AC on. The coolant temperature gauge is always cold regardless of driving conditions.

I originally thought it was an heater core issue but there is no sweet smell, and the vehicle produces hot air. I was thinking it could be the AC system issue. The AC system produces poor cold air in summer, and there does not seem to be a clogged drain hose.

There does not seem to be any coolant loss. I was quoted $1200 to $1600 to take the dash apart just to diagnose heater core, but Im not sure it's even the issue.

My car has 140000 miles.
My car has a manual transmission.

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If the leak does not contain any antifreeze or other "engine coolant" AND the leak is not due to A/C condensate backing up (if the A/C is working, just check for flow of condensate onto the ground or if this issue is occurring when the A/C is not even in use, the possibility of condensate being the source is moot, of course), then the only other possibility is a rainwater leak which leak is contained and "invisible" until you force the water out due to the operation of the blower.

If it is rainwater incursion, they may be no need to take the dash apart, rather the leak has to be sought outside the vehicle perhaps around the cowl and/or the windshield. The key though is to be sure it is not coolant and it is not condensate. If it is neither of those, it must be rainwater unless you have installed plumbing in your car. If you want to have this looked at by a different technician, a qualified professional from YourMechanic can come to your car’s location to diagnose the leak at a lower rate.

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