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Discussion Starter #1
I know few others have reported similar concerns... My rear vent blows hot air even when rear setting is off. If I set temp control to Auto, every thing is ok. The issue can be reproduced by turning off the A/C button on the screen and keep the fan running. At that time, even though the rear is off, it still blows HOT air. I lowered the rear temp to "Lo" using rear controls, still no change. It is actually blowing hot air hotter than outside temperature. Over all the cooling effect is below normal when compared to my TLX. I drove both cars today (85F), TLX cooling is far superior to MDX even after considering size difference.

I called the dealer, dealer says bring it in. Any thoughts?
 

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Talk about confusion. You said it’s replicated by turning off the a/c. If you turn off the air,what do you expect it to do? There is no cooling. Of course it’s going to be hot.
 

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I think it shouldn't blow hot air if the fan is on and the temp is set low. However, since it works in auto, I'd go with that. I leave mine on auto all the time because usually climate control works great.
 

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AUTO 68...let it do it’s job.
 

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Discussion Starter #6
Come on guys, get serious :)

MDX has 4 HVAC settings,
HEAT - Blows hot air when ambient temp is lower then setting
COOL - Blows cool air when ambient temp is hotter then setting
SYSTEM OFF - Blows air (air temp depends on recirculate/fresh air setting)
AUTO - Automatically adjusts hot/cold air depending on ambient temp/setting

When on heat mode, coolant flows through coil(somewhere near the blower fan)
When on cool mode, A/C refrigerant flows though A/C coil(somewhere near the blower fan)
When system is off, A/C will be off and coolant flow to the coil should also be off(think manual knob controlled cars)
When in auto, A/C or coolant flow is automatically controlled by the computer(or whatever)

In my case, it looks like coolant flow is not turning off blowing the hot air when in "system off" mode. You don't notice this in winter because you need hot air from the vents. In summer, the issue is clearly noticed.

Since coolant circulation is not cutting off, A/C though it is doing its job, the combination of cold & hot air is causing not so cold air blowing through the vents.

I know other have complained about sub-par A/C performance in 2014 MDX, do you think the above explanation makes sense?

So, now the question is how/what controls the coolant flow to the interior coil? may be that device/controller is bad?
 

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I don’t think coolant flow is ever totally off. I also don’t think air flow is totally stopped. Again,based on your OP. If you have the A/C off and it’s hot out,and the car is moving,there is probably going to be some hot air coming out of the rear vents. I don’t think anyone here has complained about the function of the climate control when the system is off. By turning off the A/C you are effectively turning off the system. Read your OP. You said you lowered the rear temp to low. You also said you had the A/C off. How do you expect to lower the temp if the A/C is off? This doesn’t make any sense.
 

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On almost all vehicles the coolant flows through the heater core (what you're referring to as the 'coil') all the time, even if it's 120 degrees outside. It's a pretty simple system. The heater core is in a 'heater box' enclosure that has movable ducting doors that either let 'air flow' through the heater core into the cabin or not. With an A/C system these doors can open/close in a way to have the flow from the heater fully shut off and a/c fully on or a mix of the two.

It's possible one of the doors or door controls isn't working properly such that it's stuck in the wrong position.

Regardless, if it's still under warranty take it to the dealer to check out. If it's not under warranty realize that messing with buried heater doors, etc. can be a big pain because some components can be buried behind the dash which can translate to a lot of service hours to investigate and fix. It also could be something more simple like a loose vacuum line or blown fuse depending on the design.

Luckily, the a/c and heater work fine on my 2014. I set it to 'Auto' and '70' 5 years ago when I bought it and haven't changed it since then regardless of the outside temp. It also performs fine - it's not sub-par IMO.
 

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Will check this on my 2014, but I have no complaints about the heating or cooling performance of my MDX. I usually just set to AUTO and set the temp to whatever is comfortable depending on the ambient temp. Right now that's around 20 to 22 celsius.

If you shut the A/C off (the cooling), then the rear can only blow air as cool as the outside ambient. It can't blow any cooler, and it may even be hotter as the air passes through ducts that are hot from airflow over the engine, exhaust etc. Also, to be more precise, in 'OFF', it's not 'blowing' any air at all (the blower is off) but air will flow through the system from the motion of the vehicle.

*edit*. Checked and mine is the same. If I turn the entire system 'off' I get no air flow from any vents (not sure if air enters because of fresh air mode vs recirculate because I was only going about 50km/h - at highway speed there might be more of a ram air effect taking place in fresh air mode).

If I use 'auto' and turn the rear off, I get warm to hot air from the rear vents.

Solution, as stated.. use auto mode. I'd like to check this again when it's colder outside (it's about 28c here) and see if it's coolerr air, which would indicate that it's just trying to let ambient temp air enter the rear.
 

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If all MDXs do it, then it's normal for the model. Like I said, I'd like to try this again when it's cold out and see if it blows hot or cold. If it blows cold, then I'll know when the rear is off, the system is just bringing in outside air.
 

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Discussion Starter #12
Here is the update... took my MDX to the dealer to get it checked out for $129 diagnosis fee.

They say my Heater core/unit that controls air flow is failing and needs replaced for a whopping $2600 ! :( :( :(
@mdxstang, how could be so spot on identifying the issue? unless you also experienced it.
@rcy, if your vehicle is still under warranty, get it looked at or buy extended warranty before you go to a dealer.

I was not crazy, I know what is normal and what is not.
 

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Here is the update... took my MDX to the dealer to get it checked out for $129 diagnosis fee.

They say my Heater core/unit that controls air flow is failing and needs replaced for a whopping $2600 ! :( :( :(

@mdxstang, how could be so spot on identifying the issue? unless you also experienced it.

@rcy, if your vehicle is still under warranty, get it looked at or buy extended warranty before you go to a dealer.

I was not crazy, I know what is normal and what is not.



because so much money is involved, drive another MDX and compare. Also try resetting the settings to defaults. There are many settings that can be changed and some will cause a completely different behavior.
 

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I find the A/C to be weak when in A/C on mode. We have been using Auto 68 and for whatever reason it feels cooler. That’s good enough for me.

I am not a fan of the MDX’s A/C / Circulation.
 

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Also - be aware that if the outside temperature is lower than the inside temp it will blow warm air even in AC mode. At least my 2014 did and 2015 does. When it is 60F outside we get no cooling although the air does blow. When it is 95F outside it blasts cold air. I habve to lower the inside temp when I want cold air and it is cold outside. Make sure your air temp sensor is working correctly. That temp will show in the driver's thumb wheel readout.
 

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Had the same issue with my 2014 MDX, since day 1. which i had for 3 years... i knew it was one of the heater shutter/vent flap and i just kept the rear a/c on LO, and that kept the rear cool.

3 years later, traded the 2014 for a 2016 MDX, and the 2016 didn’t have the same problem, they must have updated a part of the a/c component. it’s working properly on the 2016
 

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Yeah hmm just drove with my hand over the rear vents for a while. No problem. Front ac on, feel barely any air from the rear, but it's cold. 2016 as well.

Sent from my Pixel using Tapatalk
 

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Discussion Starter #19
Update... Filed a case with Acura Client Relations. Acura was kind enough to take care of the issue for me. I now have a working AC in my MDX.
 
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