Air vent temperature too high with A/C OFF.

[gsmollin]

In nice , cool weather, I like to drive with the air conditioning turned off, but with the fresh air vents running. Every other car I have ever driven does this simple task without an issue. But not my 2008 M35x. The temperature of the air coming from the air vents is 15 degrees Fahrenheit higher than the outside air, even with the thermostat set as low as it will go. So on a beautiful 80 degree day, the air vents will toast me with 95 degree air, unless I turn on the air conditioning. With A/C turned ON, I can set the air temperature as I wish.

Is my climate control broken, or does everybody's M35 act like this?

[Q45tech]

How do yo measure outside temperature ACCURATELY? Radio reports are measure in the shade above grass [as required by US Weather Service].

I've measured hundreds of vent temperatures at 55 mph and generally Nissans average 7-9.5F of temperature rise thru the HVAC system.

The temperature rise is a function of fan speed as the speed controller is cooled by air flow which heats air coming out of vents.

Measure the temperature of the air above the hood, as it flows into cowl for an accurate measurement of temperature gain.

[gsmollin]

I measured the outside air using the readout on the navigation display. Now I don't know how that compares to the air at the inlet side of the air intake, or in the undisturbed air in front of the hood, lacking an air-sampling probe. One other quick test I did was to measure the air temperature by sticking my air-vent thermometer out the sunroof. Doing that matched the outside air temperature the navigation display showed, so I think it is ACCURATE. The numbers I quoted were taken with the car cruising on the turnpike and the blower motor at maximum.

As I wrote in the OP, I have been driving for many years and using the fresh air systems in more cars and trucks than I can remember, and this is the first car where the heat gain in the fresh air system is obnoxious. For example, my previous car was a 97 I30, and it was never hot like the M is. What do other M owners have to report?
Modified by gsmollin at 5:33 PM 7/22/2009

[palincal]

I don't have this problem. I get cool air when it is cool outside.

M's auto climate control does select either the upper vents or foot well vents but not both at the same time except when the temperature in the cabin is same as the temperature you have selected. There is a 3 degrees range in which the auto mode will split the air between upper and lower vents. Outside this 3 degrees range, it will not split the air unless you manually change the mode.

[gsmollin]

I ran more tests, at Q45tech's suggestion. This time instrumentation consisted of type K thermocouples. One was at the air inlet in the cowl on the hood. The other was in the passenger-side duct on the dashboard. An Extech Dual K Meter was the readout. The "outside" temperature is the number on the Nav screen. I ran this test during a 25 mile commute on an overcast morning. That was good because it eliminated the sun-load problem. Here are the results:

Speed is in MPHDuct, cowl, and outside temperatures are in degrees F.

Condition Speed Duct Cowl OutsidePulling away from driveway. 10 83 73 76Local side-road. 30 82 74 76Two-lane highway 45 82 74 74Residential neighborhood. 25 83 74 72Highway 55 86 77 74Turnpike 75 82 74 74Side road 35 83 73 72Parking lot for 1 minute. 0 86 72 72Parking lot for 10 minutes. 0 96 74 72

I think this data shows what is wrong with my M. The fresh air is picking up heat from the engine compartment. When the car is moving, at almost any speed, the temperature gain from cowl to duct is 8 - 10 degrees, being lowest at the highest speeds.

When the car stops, the duct air temperature quickly climbs. In my test it had increased to 14 degrees after only a minute. After a 10 minute wait, I was being blasted with a 22 degree increase over the cowl temperature. In that 10 minutes, the under-hood temperatures must have increased greatly, even though the inlet at the cowl went up only 2 degrees. This heat load is leaking into the air duct, although the word leak is an understatement. I suspect there really is a problem.

Maybe Q45tech can comment on these results.

P. S. I apologize for the table formatting. The forum software is removing all extra spaces I used to format the table. I know there is a formatting command to preserve spaces, but I don't remember what it is, and the help file is no help. Maybe a moderator can remind me how to format a table.
Modified by gsmollin at 3:33 PM 7/23/2009

[MRider]

I have this same problem with my M45. Hot air blowing even when cooler outside. Dealer says it was normal for the M but never did any diagnosis. I always have to set recycled air or turn on A/C. I find it hard to believe the engine compartment can heat the outside air going thru the ducts to the cabin in such a short span.

GSmollin, perhaps you and I have defective or heat inducive ducts. LOL. But seriously, anyone with resolution is appreciated. Thanks.

[M4T5]

My 07' M45 does the same bulls*** too. I think it is ridiculous. Turning the HVAC system off should not allow air to travel through the AC ducts. Even if it does, it should not be hotter than the outside air. I noticed this on a somewhat cool nice night when I wanted to open just the sunroof. Well, it kind of gets ruined when the hot air from the vents passes onto you then out the roof. You would think someone here would know why this is happening. The comment about it being the same as the outside air is incorrect.This is the only vehicle I have owned that blows hot air out the vents when the HVAC system is totally shut off....Annoying

J

[SteveTheTech]

One other thing that needs to be taken into consideration is that the heater core constantly has hot coolant running through it while the engine is operating. If you are not moving air through the engine bay using fresh air mode the air that will be drawn in is the air that is being moved through the engine bay by the fan. The reason your temperature display does not change is because the element is mounted ahead of the condenser and almost any potential heat saturation under most operating conditions.

Your tests mimicked the inputs the air conditioner control unit uses to control vent temperature. Also sunload is a key input the sensor signal dictates blend door and blower speed operation. All the air that passes through the is subject to heat exchange from any number of location within the heater box. I applaud your testing but you could have easily used the car to tell you the same information with much less work. The ac system has a self diagnostic mode that can be accessed to look at the three main sensors to locate an anomalies in input signal that may effect operation.

Direct links to the above images http://picasaweb.google.com/NI...11890h ... NI...68258

The M and all modern Infinitis use a variable rate compressor that actually decreases parasitic drag on the engine dependent on ambient temperature and humidity. Even with the increase in temperature in the DC metro area I am still seeing M35s averaging ~18mpgs combined driving and the fuel consumption logs are fairly consistent. Being an owner of a classic Infiniti I know that the load on these engine is much more noticeable and the system although advanced for it's time is completely outdated for modern applications. The AC is designed to be running when the temperature control is requested. If you are looking to not increase the temperature too much use the mode switch with the blower off so air is not forced through the box but you will notice an increase in air movement while the car is in motion and air is being naturally drawn through the ventilation tract.

[M4T5]

All nice technical info, but I have yet found a mode that will keep hotter than ambient air from circulating through the AC ducts and onto me with the system turned off. Is this normal (I don't like it) or is there something that I am not doing to stop this from happening? Even on a cool to cold (not any of these lately) day the air comes out the vents warm to semi-hot. Steve, do you have anything to add to this?

J

[Q45tech]

Seems normal to me, as I discribed earlier;Give or take 1-2 F my 1990 Q45 and 99 MB AMG C43 are the same as your M45 data.

Examine the hood seal for any deformation or leaks might find 1-2 F improvement.

[maxnix]

Surely Steve doesn't mean the sunload detector affects the Vent function register air output temperature?

Maybe on the newer HVAC systems it does?

[M4T5]

Seems normal to me, as I discribed earlier;Give or take 1-2 F my 1990 Q45 and 99 MB AMG C43 are the same as your M45 data.

Examine the hood seal for any deformation or leaks might find 1-2 F improvement.

What's normal about hot air coming through the vents with the system shut OFF??? Normal would be no air at all traveling through the vents with the system shut off.I understand what is happening, but if the recirculate function was left on that mode when you shut off the HVAC system, then there would be no outside air traveling back into your car. This is what I would want when I shut off my AC in any vehicle. So far, this is the only vehicle that I have owned that does this. My Trailblazer SS has fully automatic AC controls. I just came back from driving it and when the HVAC is shut off, no hot or cool air travels back through the vents while driving down the road at any speeds. That's what we are wanting. Is that asking for too much? If an individual wants air coming through the vents, we would turn ON the HVAC system. If no air is preferred, you turn the HVAC system OFF.

J

[SteveTheTech]

The sunload sensor regulates the blower motor cycle, and not steps like the old motors and temperature trim. The sunload takes primary effect when traveling from a garage to the street to try to maintain or achieve preset temperature.

M4T5- I get what your saying, you want a sealed cabin automatically. That does not seem like too much to ask for. However that is not the way that this car is designed, the car defaults to ventilation mode and air passes through the cabin continuously coming in through the front vents (in any configuration) , the rear vents (if open) through the parcel shelf and out through the vents in the bottom of the trunk. This continuous cycle there is no stagnant air inside the car. If you hit the recirc button it will effectively seal the cabin as much as possible but that is about it.

You may want to try opening the sunroof to control internal temperature and air quality if you do not want to run the ac all the time. In the Acura I drive on long trips I regularly leave the air on fresh with the sunroof pitched open to create negative pressure to draw the air up and away. This is how I personally deal with not running the AC all the time.

Think about it this way though. With the compressor off the evaperator is not working as a heat transfer device the temperature will increase and since all the air coming through the air box no matter what the recirculation mode the system is in there will still be some heat exchange. If I get a chance I will check out what the engine bay ac lines are with the engine under full heat load. This will give us an idea of what the temperature of the gas/liquid in the lines should be. The M is designed to keep you more comfortable than many other cars on the road and it even has climate controlled seats to keep your bottom comfy.

The new AutoClimateControl has a gas emissions sensor mounted behind the front bumper that detects levels of emissions from the surrounding vehicles. The output of this system is to close the recirculation door for you. They also incorporate an Ion filter and specially designed odor reducing air filter. Currently though this system is limited to the G37convertible and the FX50s. These systems are getting more advanced as time progresses but there are always going to be things that some people wished did other things.

Nissan has used a fairly advanced AC control system with it's auto models since the day of the dinosaur Infinitis. While many of the domestics were still using vacuum lines to control blend door operation Nissan was using a self detectable solenoids to monitor its operation. They have been using three sensors to control output trim for decades.And they have always defaulted to fresh air mode.