FishNoGeek — Are you quite sure that the actual air temperature is hotter. If the air velocity is different, it will feel either hotter or cooler to the skin, even if its actual temperature is the same. I don't think that the air velocity is the same from the front and rear vents. Measuring the air temperature with a thermometer should answer this question. Perhaps this is what you have already done?

Stan

 

Stan,

That's a good point, and I haven't gotten so scientific as to dig out the thermometer. I will, great call.

That said, we're fairly certain that it's temperature. The litmus test there is how we discovered it in the first place: my wife and the baby were in the backseat and baking while I was basking in nice cool A/C air while driving. That's happened a couple times; we'll find ourselves uncomfortable, then discover that there's a big difference in temperature between front and back.

Thanks....anybody try this themselves yet?

 

I tested mine on the way home today and I see what you mean. The center rear vents do blow considerably warmer than the passenger side vents when the climate system is in Dual mode. The passenger temp dial still adjusted the temp of the air out the rear vents, but I'd say the rear vents felt at least 7 or 8 degrees warmer than the passenger vents through out the mid range temperature settings. On the last 2 or 3 settings before LO (metric 18.5C, 19C, and 19.5C which is mid to high 60sF the passenger vents felt slightly cool to neutral whereas the rear vents were still blowing noticeably warm. When I switched to LO, only then did I get cold air out of the rear vents.

 

I have noticed that under the "B" marking for the shifter, there's a spot that gets warm after 10 or so minutes after I turn on the car. At first I thought it might be an incandescent light but I'm pretty sure that the shifter letters are lit by a diode. My next guess was that it might have something to do with a piece of hardware associated with the hybrid part of the car; maybe the wire from the battery to the motor is carrying heat too or maybe there's a switch, relay or another device that dissipates heat. The batteries do get really hot. If the (thermally insulated) plastic on the surface is warm, it must be really hot under it. This same heat might also transfer to the a/c ducts. I do not have any other problems with my car so I assumed this heat was design (for better or worse) rather than a defect. Can anyone else confirm this heat under the "B" marking of the shifter?

 

Here are a couple of the air-conditioning system diagrams from the "New Car Features Guide," posted to this Web site. See if you can figure out what air goes to each vent, and what controls its temperature!

Stan

 

It appears that the rear outlets are controlled by separate dampers than the front, so I guess it shouldn't surprise that there can be a difference.

At middle temps the front (passenger) damper allows a mix of air passing thru the heater core and air bypassing the heater core. The rear damper then seems to try to provide it's own mix of these two air streams after the heater core rather than simply use the mix already being provided to the front passenger.

 

I finally ran into this problem last weekend. My temp was set to 74, while the passenger's temp was set to 77. The AC was on in fresh mode. The rear passengers asked if the heat was on. Yes, for many of you 77 is heat, but the air coming from the front passenger's vent seemed close to 77 while the rear vents were blowing air that had to be closer to 85. I don't know if this is some new glitch because I seldom have people in the back seat.

Although, if this were common, I would expect many more posts in this thread.

 

I have also noticed at one time considerably warmer air blowing out of the center console rear vents. It was not long after I got my TCH, and I can't remember the settings I had at the time on the A/C system. I haven't noticed it since which might be because of the settings I normally use now having settled into my "routine" with the car. I normally set my A/C for 71-74 F.

I remember wondering at the time if the longer ducting to the rear vents was that much warmer (due to outside conditions) to heat up the air passing through it. Unfortunately my son was in the back seat and I didn't want him to bake, so I couldn't let it run to see if the air cooled after the ducting had time to cool (I just shut the rear vents off).

 

FishNoGeek — It appears that you are indeed right about the hot air! There's a new TSB out on this issue. I have posted the Canadian version as CDN_TSB2940 "Rear HVAC Vents Blow Hot Air with AC "ON"" in the thread "List of pertinent TSB's."

Stan

 

Most important for this test.....be sure both temps are set the same....