Nissan Repair: Infiniti QX-4 Leak under floor mat, competent mechanic, fan blows air

Question
QUESTION: Hi,
I have a 2002 Infiniti QX-4 with 65,000 miles. The passenger side carpet under the floor mat is wet. It is definitely not related to rain. I dried it out and the next day it was wet again and we had no rain. I googled the problem and came up with the answer that it may be a plugged evaporator case drain tube.I brought it to my local repair shop and they blew out the tube  and said it was clear, there was no blockage, but they did not explore the problem any further. Any ideas as to what it could be? It is plain water. I am not using AC now, I am using heat, I live in NY so we are definitely not using AC now. Thanks

ANSWER: Hi Jeff -

The only other thing it could be is the heater core leaking. This is located passenger side of the car, usually behind the glove box. Hot water from the engine passes through this core and when it calls for heat, the fan blows air through this core, resulting in heated air for the interior of the car.

Here in Hawaii, we usually disconnect it as there is no need for heating. But obviously where you are you will need to replace it. The work is a bit cumbersome as you will have to dismantle the duct work and be able to work in tight places. Best thing is to take it to a competent mechanic if you don't have the time/tools.

Hope this helps -
aloha
calvin

---------- FOLLOW-UP ----------

QUESTION: If it is the heater core leaking, would the liquid be antifreeze or water? I am pretty sure it is plain water, not antifreeze.  

Answer
Hi Jeff -

It would be whatever you are running in your cooling system. Some use plain water. If you are using coolant, then yes, it would be coolant leaking.

Other than that I cannot think of anything else that would leak water over there, you already have eliminated the other 2 that would cause this.

Try having your cooling system pressure tested anyway and see what happens.

Hope this helps -
aloha
calvin