I have an 08 G35S.

On the way to work in the mornings, the climate control is set between 76-78 degrees and the same for the passenger side. The outside temp is usually in the 40s-50s. Warm air comes out of the vent (as I want it to) and all is well.

On the way home in the afternoon, the climate control is set at the same temp. The outside temp is usually in the 50s, but can vary between 40-70s (Texas). Being in a cold office all day, I still want warm air, and having changed nothing, I expect it. But after it being warm for a brief moment, the air out of the vents turns cold. Not a/c cold, but definitely not warm. Any thoughts for why this is? Does it sense the outside temperature and adjust accordingly? I looked in the manual for tips about the climate control and auto climate control, but I still have the same problem (whether it's on auto, or manual). I wish it had a **** by the vents (like an 08 BMW) where even after you set the temperature, you can adjust the **** to have it be warmer/colder - depending on your preference. Appreciate your thoughts and input.

 

Is the HVAC set to auto or on manual? If it is on manual then it will blow cold air as the heater takes time to blow hot air on a cold start... leaving it on auto corrects for this by not increasing fan speed (and using foot vents vs front) until the car heats up, allowing heat to rise. Can shift vents from auto to front vents when air fan speeds up on auto as it means the air its warm.

 

First off, I'd sweat to death if I set it at 76-78 degrees. Second, if it's 50-60 degrees outside and the sun is shining, it could easily be warmer in your car than your set temperature, thus causing your auto-climate control to push out cold air. I'd say that more than likely it's functioning just fine, and as most other auto-climate controls do. If you still want warm air blowing, crank up the temperature setting.

 

I have the same problem with my 2008 G35x. I posted the same "issue" on this forum a few weeks ago and didn't get any good feedback. I do not use the "auto" feature and it seems that I am constantly having to change the temperature setting after about 15 minutes of driving to keep it blowing warm air, as after about 15 minutes the air is cool and I didn't change the temperature (typically I leave it at around 70 and it has been around 32 where I live for the last 3 months).

 

Sorry to resurrect this but I am having the same issue as Scottmn4. Has anyone figured this out yet? Car is not set on "Auto". Blows warm for about 15 minutes then all of the sudden I get a blast of cool air from the vents.

 

Sub'd for an answer.

 

In my experience our car really takes awhile to blow hot air from a cold start. LA weather is getting cold and I turn the heater on from a cold start (auto/manual) and find out it took about 10-15mins before my car really blow some hot air. But about the question why all of a sudden the car blow cold air My theory is "when our car is on stop/idle not too much hot air comes out (sometimes cold), Only when were driving thats the time our car really blows hot air."

 

Here's an update:

It's been really cold in Chicago this week. I've noticed that the heat isn't cutting out anymore. I'm wondering if outside air temps have anything to do with the heating system?

 

I concur. It has been very cold in Fargo, ND over the last week and the heat does not cut out when it is very cold outside. It does, though, if it is warmer than 20F outside and it is really annoying. It is really the only complaint I have with the car.

 

I'm not sure about our cars on this, but I have seen on other cars (BMW) where the air temp automatically changes in the vents blowing directly at the driver. Take it for what it's worth, but as the tech explained to me at the time, apparently it is by design and was intentionally done to to prevent drowsiness of the driver.

 

Kind of an update:

Taking the car in tonight for an oil change so I called and spoke with my service writer about the heat. He made it sounds like it's not normal, but also told me to keep the A/C on when running the heat to help remove moisture from the system and it also helps keep the compressor's seals lubricated. Not sure if this is fact, but, I will use the heat with the A/C on for a few days and see if it helps. Otherwise, it's back to the dealer for them to diagnose it.

 

Update to my Update:

No change when running the A/C with the heat. Same thing happens. However, I'd like some people to try this:

1. Start your heat (with AUTO off) with it blowing just on the floor and let it run for about 10 minutes.
2.When it starts to get warm, slowly turn the temp down\cooler. See if the your system automatically changes the air direction from just the floor to BOTH floor and vents.
3.Then, slowly turn the temp up and see if the air direction changes from floor\vent to just floor.

I just found this out last night. I'm guessing it's normal operation, but if anyone else wants to give it a try, let me know if you get the same outcome.

 

I was having a similar issue with cold air blowing and also recently developed the issue where cold air always blew out when I was stopped at a light. Considering it's gone down to 10 degrees here I wasn't about to put up with that for long.

From experience I knew that if you're blowing cold air at a stop then either your coolant is low or you have an air pocket trapped in the heater coil (typically one or the other as far as causes go). My ex girlfriend's mitsubishi eclipse was notorious for taking in air in the system before and after I replaced the hoses so luckily I knew what to do.

For my case I inspected the system last weekend and realized that my radiator wasn't even full to the top. I topped off the radiator with some 50/50 and filled the overflow tank almost to "max" (this is per the owner's manual direction). This make the overflow tank the high point in the system so hopefully the air will migrate to the tank. Otherwise, with my ex's car, I jacked up the front a few inches off the ground and ran the car with the radiator cap off. I placed a funnel in the radiator fill opening and filled it with coolant to make it the high point of the system. Eventually you will see it start bubbling and the level in the funnel will decrease as the air leaves the system. It takes about 15 minutes but it worked very well. Once done just top off the radiator and the tank.

I hope this helps you. At a minimum fill your radiator and overflow tank if you haven't done so already.

- Bob

ps - I NEVER run the system in "auto" and still had this problem. Also, I always ran it with the AC on. I have stopped doing so in the past few weeks just as an experiment with my gas mileage. My issue occurred in both settings.

 

So 3 years later and this problem is getting worse and worse. Has anyone ever figured this out? It's not air in the system, there's another issue going on with whatever mechanism is modulating the heater coil flow from what I can tell.

 

Are you still losing coolant? Your car should not be losing any coolant.

Also, topping off the radiator and overflow tank will not properly bleed out the system. There are instructions out there for proper bleeding of air from the system which includes loosening the bleeder screws on a hose and the radiator. Bleeding the system is more easily done if you have a Lisle funnel.