I've seen references to this problem on the G35 sedan at FreshAllow.com. Owners complain that on cool mornings and evenings, when they turn off the AC and select outside air, the cabin heats up as if the heater is on, which it is not. I haven't tried this in my week-old G35 yet because it's just too hot here in San Jose.

However, I wanted to mention that I had a similar problem with the 2002 Sentra Spec V that I just traded in for the G35: last April, during some cool Spring days (about 55 to 60 degrees outside), the cabin got very hot after the car had been running for awhile whenever I selected outside air with no AC or heating. I finally had it checked out by Nissan's west coast service manager, who installed temp sensors around the vents and cabin. He got interiror readings of over 95 degrees after 20 minutes of freeway driving from a cold start. He explained that on the Spec V's B15 Sentra body, the channels that route outside air into the cabin are situated very close to the heat shield behind the engine; because the heat shield was admittedly very poorly insulated, the heat buildup from the engine was transferred to the air inlet channels, which then sent very hot air into the cabin. He suggested I use the AC all year round to avoid this problem.

When I purchased the G35, I assumed that the problem would go the way of my Spec V. I'd hate to think that Nissan/Infiniti have implemented the same poor design on the G35. Guess I'll have to wait a month or so before I can check it out myself.

 

I've experienced the warm air a couple of times but usually I just change the mode to recirc and then shut the system off. This keeps the warm air from the engine or exhaust or wherever its coming from out of the cabin.

 

I found a vent below the the dash (next to the right foot) that is constantly blowing hot air even when the engine is hot (and AC off) I am not sure what that vent is for but i am going to block it.

 

Confirming Merlin's post...

I just pulled the battery cover off while the ventilation fan was running at full speed. A large volume of air is being sucked into the inlet directly behind the battery. Even with the battery cover replaced, only a small fraction of that air is entering through the vents below the windshield wipers. Can you tell where most of the air is entering? What could they possibly be thinking to vent the battery into the passenger cabin? I’m wondering if these is a way to retrofit a real fresh air intake.

<P ID="edit"><FONT class="small"><EM>Edited by rowland_physics on 10/14/02 05:12 PM.</EM></FONT></P>

 

I just did a little investigating to see if the outside air and battery fumes are commingled in the G35 ... THEY DEFINITELY ARE! Here is a 5 minute experiment you can do verify it for yourself:

1. Open the battery cover. (To the rear of the battery, you should now see the ventilation system intake that goes through the firewall.)

2. Turn the ignition key to “on” and turn the ventilation fan to full speed manual.

3. Place your hand behind the battery and you can feel a large volume of air being sucked through the firewall into the ventilation intake. (For a moment, I thought that maybe this air was coming OUT of the firewall vent to provide a positive pressure to vent battery gasses AWAY from the battery compartment. A quick test with a piece of paper ribbon proved that the air is definitely being drawn FROM the battery compartment INTO the interior of the car. - All charging batteries give off hydrogen gas and hydrogen sulfide fumes. This has GOT to be a health/safety issue. )

Here’s the part that is still puzzling me:

Put the battery cover back on. Keep the ventilation fan running on high. Feel how much air is being drawn into the two small inlet vents next to the driver’s side windshield wiper.

Observe:

The volume of air being pulled through the firewall is FAR greater than the total volume of air being pulled through those two small vents. Where is the additional air coming from? Is there another opening below the battery? (If you look at the identically shaped compartment on the driver’s side of the car, you will see a hole in the “floor”. Maybe the battery side has an identical hole.)

Solution: I think that we need to pursue this with Infiniti from a health and safety perspective. It may be our problem that we have a fresh air ventilation system that blows warm air on a cool day, but I think that Infiniti has a design flaw that has definite health and safety ramifications. The plastic air duct (plenum?) looks like it could be redesigned to bring air from the passenger side of the windshield directly down into the fan intake. I’m going to start lobbying for a retrofit.

 

Continued discussion on Freshalloy about this. There is disagreement on whether the cause is heat soaking into the cowl and battery ductwork or if the climate control system is heating air unnecessarily. Here is what I posted over there:

Somebody (me?) needs to determine on which side of the firewall this problem is occurring. If I get time this weekend, I will try to set up a data logger with three recording thermometers ... (1) outside ambient, (2) at the fresh air intake inside the battery compartment and (3) at the vent outlet in the passenger compartment. Only by looking at these three temperature readings under a variety of conditions will we make any progress on this issue. If there is a substantial difference between (1) and (2) I think we can blame the ducting. If the difference is between (2) and (3) we can look at damper, heater core design or ECU issues.

If it turns out to be the ducting, and Infiniti is unresponsive, I am considering cutting some slots (or drilling some holes) in the passenger side of the cowl ducting (where the inlet *should* be). I am also thinking about trying to design a baffle, to keep battery fumes from commingling with the intake air. Maybe this is a safety *non issue* but is still disturbs me.

What do you think?

I have been keeping my temperature at 60 (rather than 61 or 65) and it *does* (but shouldn't) seem to make a difference.