I searched but didn't find anything, but lately, when I turn of the vents to defog the windshield, only the driver side works.

I noticed that the passenger side does feel colder than the driver side. The dual mode is off.

May take it to my mechanic to look at, but wondering if something is failing. No lights are on.

 

What do you mean when you say "I turn off the vents to defog the windshield?" You shouldn't have to do anything with the vents. Just press the front-defrost button. The car should direct the air where it needs to go without you doing anything else.

 

It's not a lot of info to go on, but the very first thing I would check is the actual A/C system's charge. Usually when the drivers and passenger's side vent temps differ, this charge is low. I have seen this multiple times at work. This could/would explain why only have the windshield clears with the defrost on. Make sure your mechanic doesn't just charge the system and ship it back to you, but instead he should def check for leaks/add dye/etc. Good luck, let us know what he finds then

 

I'm thinking a blower system door isnt moving correctly when switched to defrost--

does that sound right acuratech239?
we appreciate your pro input on the threads!!

ck'd the cabin filter yet?- should replace every year
gives you a chance to look for obstructions in the ducts and vac out leaves and crud that gets in there from the inlet

dont close off the dash vents to force more air to defrost- it will take care of itself,,
do turn the fan down if using manual controls,,tough on the door mechanism to switch when fan is running at full speed

have a read of the owner manual on temp control system

have ac freon pressure/level ckd as acuratech suggest
use a `dye added` freon if its low- find the leak!

 

01tl4tl -

Well one of the reasons I don't think it's a mode door is because that wouldn't affect vent temps, and because the defrost is all or nothing. In the 3G TL, you can have your dual mode as vents on face, feet, or face and feet, and differ those in any combo between pass and driver. But, if defrost is selected, both pass and driver go to defrost; you can't split just half and half. Therefore, since he states only have the windshield clears, we know defrost is working. And if it was temp door problem, the defrost should still funtion regardless because the A/C is switched on, and blowing the same dry air, just at a warmer temp (which is why defrost works whether you have the temp set at 59F or 69F, etc).

Add to the the different vent temps, when on other settings, and I'm still leaning toward a low charge in the system. Not trying argue with you, just getting into a bit more detail on system operation! And again, seeing this in person (at least the different vent temps, I've never personally had the defrost only working on one side complaint), this is my reasoning for my suggestion on fixes. It would be easy to check for DTCs though, all you would need is the HDS and go under body electrical, and then HVAC. Further, with the HDS, you can do an actual HVAC test even if there aren't any DTCs. I believe the above things can be done without the HDS, but I don't know the exact procedure since I always use the HDS. I could investigate and post more if desired.

As you mentioned though, this is a good time to inspect, and replace if needed, your A/C filter! And I'm glad you appreciate my input, it's nice to hear

I still hope the OP gets back to us with what he finds.

 

I'll second that... I'm dealing with a no defrost issue...

 

great info.

I wonder if he's hitting the defrost button, then switching the vents off manually, and it's kicking into (or back to) "dual" mode at that time, with different passenger settings.