could be a water leak from the cowl into the heater box itself....

there are a few threads on here about water leaks on the floorboards and in the dash.

Id check the heater box, basically take out the glove box itself to get access under the dashboard, have someone rock the car a bit and the water should move for you to pinpoint it.

Im sure the glove box comes out, just dont know how. Ive had this issue on the s-10s and s-15's ive owned in the past. hope it helps


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