Hot air coming into the cabin

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.
 
hey Lith..i will definitely follow your advice. Regarding the broken heater valve, Sparky here posted the same issue of having cabin heat. He suspected that the HCV was broken so he replaced it and adjusted the cable properly - this didnt solve the cabin heat issue. Both Sparky's CCU and mine were previously repaired by BrianK. I was wondering if your CCU has been repaired also?
 
If the heat valve is closed and the system is put on recirc and you still have a heat issue the hvac system can not be the source of the heat.
You are probably right Brian. Thanks for your input.

Per Lithiumus advice, I drove the car for an hour, opened the hood and indeed the fan is blowing so much hot air towards the firewall. The blower and the firewall were really hot to the touch which tells me that the heat could still be finding its way inside the cabin. I will remove and re install a different/better foam seal to the blower and see if it will solve the issue.
 
I also have been at this issue for a few yrs now and basically learned to live with it lol. So I've insulated and taped up the blower motor in the front, tighten the cable slack, and have the R hood with the round radiator ducting. Even with the sides of the radiator sealed up ( hood duct does not completely seal the sides of radiator) no luck. Recirculation pressed doesn't help either. Heat is in the footwell / dash area and not coming through the vents. Hope this info helps narrow other solutions.
 
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This weekend I was on a nice long cruise with the NSXCA club and decided to troubleshoot and verify the results of tightening the slack.

What I can say for certain, is that there is no hot air coming from within the radio cavity any longer. I suspect that either my floor/side ducts were not connected properly and hot air escaped or I had left my JDM Nav pod off and hot air came in from the center vents. So...

It seems the real problem is that even if my temp is set to full cold, I still get hot air coming in through the vents. The same hot air comes in whether the CCU is set to Fresh Air or Recycled air. Just to test the temp/valve, I set the temp to full heat and the hot air was even hotter. I could barely leave my hands in front of the vents for very long the air was so hot. So I know the valve seems to work as the temp does change but the problem is that I'm getting hot air coming through the vents no matter the heat or circulatory settings. At least in my case, I can say that the heat it 100% coming in through the HVAC system and not through another source.

I'm looking at JRZ's comment as well as jagtiger's and I'm wondering if the blower is heating up to the point where the entire assembly is so hot that the cool air is being heated by the blower's radiant heat and blowing in hot air. Other than that, the only thing I can think of is a broken coolant valve letting some coolant into the heater core and the air mix door stuck open and always allowing air to pass through the heater core...
 
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Your valve could be broken too- even when the slack is gone, it sounds like it is not closing all the way.
 
Okay guys here are the things that I did to try to fix the cabin hot air issue:

1. Take the cable out from the heat control valve and leave if on "shut" or close position - no success
2. Replace all seals in the heater blower unit - no success
3. Installed a DF radiator duct - no success
4. Cover front cowl intake - no success

After spending a lot of time and $$$ - I found a used heater control valve in ebay. Installed it over the weekend and has been driving the nsx for a couple of days now. So far NO hot cabin air issue - I will continue to drive the car for the next couple of days to see if this actually solved this gremlin. Wish me luck ;)
 
UPDATE: After replacing the heater control valve and keeping it in "shut" position - the cabin heat still exist! :(
 
Your ac is operational? The nsx needs ac down to about 40 degrees.

Hi Brian, so today my AC started acting up. So turned it on as soon as I left work and was blowing cold air for 10 minutes then for no reason it started blowing hot air. It was so hot that it seems the heater was on instead of AC. It was hot air for half hour or so then it started blowing cold air again until I reach the house. This is very strange and the first time it happened since after my CCU was rebuilt.

Would this be a CCU going bad?

Please let me know. Thanks Brian
 
Hi Brian, so today my AC started acting up. So turned it on as soon as I left work and was blowing cold air for 10 minutes then for no reason it started blowing hot air. It was so hot that it seems the heater was on instead of AC. It was hot air for half hour or so then it started blowing cold air again until I reach the house. This is very strange and the first time it happened since after my CCU was rebuilt.

Would this be a CCU going bad?

Please let me know. Thanks Brian

I would guess you are getting low on freon, but it could be a sticking expansion valve or even problem with the fan cooling fan control unit.
 
Thanks for the quick reply Brian. I did the check the freon with a gauge and looks like its in the proper level. Also no bubbles in the sight glass. :(
 
You guys with hot air coming into the cabin might want to make sure there isn't a tiny politician lurking somewhere in your footwells.
 
you guys with hot air coming into the cabin might want to make sure there isn't a tiny politician lurking somewhere in your footwells.

lol!
 
Other then tracing back the compressor run signal I don't know what else to tell you.

I drove the car today and ran the AC full blast in the coldest setting - AC not working only warm air coming out. I then switch the setting maximum heat and full blast fan - the fan stop and completely no air coming out except in the footwell area. I tried switching to cold and heat but got the same results. I'm thinking my CCU is probably the culprit. :(
 
I drove the car today and ran the AC full blast in the coldest setting - AC not working only warm air coming out. I then switch the setting maximum heat and full blast fan - the fan stop and completely no air coming out except in the footwell area. I tried switching to cold and heat but got the same results. I'm thinking my CCU is probably the culprit. :(

You are welcome to send it back and I will put it on my test fixture and see if I can find any issues I assume you have run the test procedures?
 
You are welcome to send it back and I will put it on my test fixture and see if I can find any issues I assume you have run the test procedures?

Thanks Brian I will run the test procedure today and will keep you posted. I really appreciate your help. ��
 
Thanks Brian I will run the test procedure today and will keep you posted. I really appreciate your help. ��

Hey jagtiger,

Bringing this thread back from the dead since no one has a definitive solution to this. Its also possible that buying a used valve could simply be buying a valve with the same problem.

Maybe the valve deteriorates over time and/or the AC compensates for it and people just dont notice it.

Since im driving the car every few years... ill look at the issue again! Hey jagtiger, if you still have your original valve, think you could send it to my for inspection/disassembly?


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Hey jagtiger,

Bringing this thread back from the dead since no one has a definitive solution to this. Its also possible that buying a used valve could simply be buying a valve with the same problem.

Maybe the valve deteriorates over time and/or the AC compensates for it and people just dont notice it.

Since im driving the car every few years... ill look at the issue again! Hey jagtiger, if you still have your original valve, think you could send it to my for inspection/disassembly?


Sent from my iPhone using Tapatalk

Isn’t the hot air coming into the cabin a result of failed foam in the heater box? My issue was the foam gasket between the blower box and the body of the car (under the hood).


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Isn’t the hot air coming into the cabin a result of failed foam in the heater box? My issue was the foam gasket between the blower box and the body of the car (under the hood).


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Thats definitely one of the causes but both jagtiger and I were getting warm air from the air vents. I was not getting any leaks from the foam seal. The hot air seems to likely be from a failed coolant valve allowing some hot coolant into the heating elements and thus heating the air.

Im ordering a new valve to see if that fixes it.


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