I had the classic issue of heat coming into my cabin when driving at speed, even with A/C set to full cold. In my case, it was coming in the footwell. A very nice NSXCA member at the 2012 NSXPO showed me how to adjust the water valve cable under the hood vent valence (on the coolant pipe going into the firewall). In fact, he adjusted it right there at NSXPO and problem totally solved. Took all of about 10 seconds.
The issue is that over time, the cable leading to the heater control motor slips in the retaining clip, which creates slack, which means the water valve does not close completely and hot coolant circulates through the heater core- even when set to full cold. All he did was unclip the retainer, pull the slack out of the cable, and re-clip. Garrick, before you disassemble your HVAC, you should check this simple fix. BTW, your powdercoated covers are still going strong on my NSX. They are one of peoples' most-appreciated things about my NSX at car shows.
Paul, it sounds like you hit the nail on the with this one and I'll check this before anything else.
Also... it's comments like this that keep me (ever so slowly) producing powder coated covers! My wife keeps flogging me about my "failed business" and when I tell her it takes me about 25-30 mins to mask each individual cover to prep for coating she ALWAYS reminds me "do you know how much you make an hour? you are bleeding your guts out on this yet you keep going...". But every time someone drops me a nice line or when they pick up their covers... I get job satisfaction even if my guts are all spilt over it!
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Hey Jagtiger, another thing you can do to confirm the issue is stop the car and quickly pop the hood and see what kind of heat is in the underhood area. If there is a lot, I think the duct will definitely help redirect it out the Type R hood vent but that won't help others who do not have a Type R hood. while you have the hood open, you can also check the temp of the firewall esp. if you were on the highway.
It's possible that there are air leaks between the firewall but I think it's unlikely. Another test to confirm that the heater core inside the dash is not warming up is to take the glove compartment off and when you feel the hot air after 20-30 mins, stop and go to the passenger side and touch the evaporator (white plastic unit) near the bottom and feel if it's hot. If it's hot, your valve may be broken, not working, or wrong position as there is coolant heating up the core.
Logically there is also a chance that the valve is leaking coolant even in closed position and the gates that close off the airflow to the heater core isn't closing 100% and you are getting warm/hot air leaking into the vents. Sounds very unlikely as well...
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I just checked my cable and it had a bit of slack. About 3-4mm so it was definitely letting in some hot water. Check service manual page 22-66 and 22-67. It's part of the evaporator removal section but tells you about the slack.
Just unclip the wire and lift it off the arm. Turn the car to IGN2 and set the climate control to full cold and it should retract all the way in. Put the cable back on the arm and push the arm inward all the way. Then use your hand to push the cable in through the firewall until it's nice and tight pulling the valve fully closed... then clip the cable again. I'll test it out next time I'm on the road.
