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Hi Everyone, new to the MDX crowd. After reading a bit around,, it seems we have knowledgeable people here. Well, I've had my new 2017 MDX- advanced SH AWD, for about 3 weeks and about 1000 miles. Seems to be a nice vehicle, though not what I expected.

I have a heating issue, maybe someone can clarify, or may have had. As you might know, it's been a little chilly here lately, sub-zeros here in northern NY. My problem is the heater only blows hot while the vehicle is in motion, and starts blow cold while stopped or parked, thus making my remote starting useless. Also, the blowe r for the feet blows cold, not ideal up here.


Any ideas or suggestions before I call the dealer after the New Year?

Thanks in advanced.
 

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First question to you is how are you using the heating/AC system? Are you in full AUTO mode or manually controlling the temp, fan speed and direction? In cold weather I would suggest using the full AUTO mode with the temp set mid 70's. Also put the seat heaters in AUTO helps with the total comfort. In AUTO I have noticed that the fan speed and direction is always changing to keep me comfortable.
 

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It shouldn’t matter what mode the car is in. Once it’s warmed up. It should be blowing hot air. Unless you don’t have the fan on. In which case air is only blowing when the car is moving. Previous post is correct. Keep it in AUTO.
 

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If it's a new 2017, it should be under warranty. Go back to dealer. Sounds to me like a defective thermostat (hot when in motion, but cold when stopped or parked), or maybe underfilled on coolant. However, it could be any number of things do with the heat / AC system, like a blend door not working properly etc.

Full auto or manual shouldn't matter - if he selects heat (whether manually, or automatically), the car should blow heat whether it's moving, stopped, parked etc.
 

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Yep, I agree it's time to see the dealer.
 

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MDX heater issue

I have a 2015 Acura MDX and have the same problem. I have had it in the dealer shop 3 times now. They have put a larger floor vent (still cold). Today they told me it is a well known problem and they cannot fix it. I was told that the engine is so fuel efficient it shuts down the heat when idling slower to give me good gas mileage. I DON'T CARE ABOUT GAS MILEAGE....I want HEAT!

They told me to call Acura Canada (yes I live in Canada with a vehicle that does not give me heat) and complain and maybe if enough people complain they may get a fix for it. Is this ridiculous or what?

I am now looking for a new car!
 

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Other than the single post count OP that started this thread I haven't read much about it, so I find it hard to believe this is a well-known or wide spread issue. I also can't process the idea of a larger floor vent; #1 where would the dealer find such a thing and #2, why on earth would any dealer think a larger outlet is going to change the air temp?

If you're genuinely having a heater problem, then go ahead and call Acura Canada because I don't think anyone here can help. Please post back the solution so we can build our knowledge base.
 

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Other than the OP,who was never heard from again. This does not appear to be a wide spread problem. Find a dealer who knows what they are doing. What a bunch of BS from the dealer. Now if you have auto stop/ start,that may have a little effect. But not cold.
 

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One post by the OP. This thread was started nearly a year ago. Guess it was not a problem after all.
This is a problem as my 2014 MDX is having the problem now. It is at the dealer now. They flushed my radiator, as it was told to me that it was dirty and that didn't work. I'm waiting to see what the issue is now, as I took it back.
 

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the air temp in part is set by a comparison with the outside temp and the inside temp. For example - in both my 2014 and 2015, if it is 40 F outside and the temp inside is set on 70 F I will get warm to hot air most of the time until the car is 70F inside then it simply recirculates. If the temp is 100F outside and the inside is set to 70F it gives very cold air. If it is 70F inside, and 70F outside then it gives ambient air with neither heat nor cold. You can over ride this with manual settings but they can be confusing. It took me awhile to figure them out because there is a temperature setting, a fan setting, and a vent setting. And, the amount of heat or cold is not constant - meaning that the colder you set the manual temp the colder the air blows - but that does not change the fan speed or where the air goes when it comes out of the vents.



I would think that if someone lets the car sit in a garage and lets the engine heat up in that confined space, the outside temp sensor would read high, perhaps as high as 80F - 90F because engine and radiator air is circulating up into it. Then when someone puts the inside of the car at 70F the computer looks at how hot is is outside 90F and decides not to blow hot air into the car regardless. The manual indicates that letting the car sit will cause the temperatures to be off.
 

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I have a 2016 MDX and have run into this same issue this winter. I've been to 2 dealerships, they tried a rad flush and replace the heater core. They've since told me it's a common issue that they don't have a fix for. I'm currently fighting with Acura Canada but not getting anywhere. Wondering if anyone has had a similar experience.
 

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run the temp up to full hot and see what comes out the vents at that time. Then lower it until it feels comfortable. Also there is a manual calibration for the outside temp. What does the temp show on your dash when this happens, is it reasonably accurate when it happens - meaning is it 30F outside and the car shows 30F outside?

The inside system looks at the temps in the car and outside when it decides what to give you air wise. It doesn't always seem to follow what you and I might consider warm or cold. For example - you are stopped in traffic, stop and go, stop and go, The outside temp will read way high because of hot air trapped in the engine compartment. In that case the system won't give you as much heat as you want. Run the temp gauge warmer and warmer and suddenly you will start to get heat.
 

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The temp runs full hot when the car is moving. As soon as I come to a stop or first thing in the morning when I'm trying to warm the interior up it blows cold air, it doesn't matter what temp I set it at. The outside temp gauge is accurate. I've had the vehicle for 4 years, it's the first time I've had this issue and like I said Acura has no fix for it, essentially it's a design flaw.

BTW, current temperature outside is -33C.
 

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At the below freezing temps it takes time to heat up the coolant that flows into the heater core to warm your air. At -33C (OMG!) it'll take a half an hour of idling to even feel warm air coming out of vents on any vehicle. Your lower coolant hose will stay cold and the thermostat wouldn't probably get open at all even if you drive for a while. Check the hose that goes to the heater core under the hood (smaller diameter but don't mistake it with an AC tube foam jacket). Just watch your hands and clothes so you don't get caught by moving belts/pulley or the rad fan. The hose has to be at least warm on touch after 10-15 min of idling in any weather. If it's cold - you have a low coolant issue. You're saying the air gets cold when you stop- clearly the coolant lever issue or your water pump is giving up. If you feel your heater hoses hot but the air blows cool at the hi heat setting- there you have a heat exchanger door stuck or its actuator faulty. Hope it helps.
 

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At the below freezing temps it takes time to heat up the coolant that flows into the heater core to warm your air. At -33C (OMG!) it'll take a half an hour of idling to even feel warm air coming out of vents on any vehicle. Your lower coolant hose will stay cold and the thermostat wouldn't probably get open at all even if you drive for a while. Check the hose that goes to the heater core under the hood (smaller diameter but don't mistake it with an AC tube foam jacket). Just watch your hands and clothes so you don't get caught by moving belts/pulley or the rad fan. The hose has to be at least warm on touch after 10-15 min of idling in any weather. If it's cold - you have a low coolant issue. You're saying the air gets cold when you stop- clearly the coolant lever issue or your water pump is giving up. If you feel your heater hoses hot but the air blows cool at the hi heat setting- there you have a heat exchanger door stuck or its actuator faulty. Hope it helps.
Thanks. I should clarify, the issue arises after the engine has warmed up, so I'll be driving and the heat is working fine. Once I come to a red light and the vehicle has stopped it starts blowing cold air, this happens at any temperature. I had the vehicle inspected by 2 dealerships, both told me it's been an issue with some of the 2014-2017 MDXs. Neither offered any solutions which seemed odd, but my guess is they've seen and tried many different things but nothing has worked long term and they didn't want to charge me for a bunch of work that they knew wasn't going to work. Which I can appreciate but doesn't help the situation.

What I've noticed since the extreme cold left is that when the temp is set at 20-21C it seems to work fine (this is post heater core replacement). When it was below -20C we would need to set the interior at 23-24C to keep up. At that setting, the issue of blowing cold air re-appeared when the vehicle came to a stop. So an improvement but still not working the way it had been the last 3 winters.
 

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I understand there is no valve that controls coolant flow to heater core, so there is nothing that is stopping the coolant to flow and output warm air. Is it possible that water pump is kicking on only when the car is in motion?
Can't think of any other reason. Do you notice an abrupt change in air temp when you come to a stop or does it take few seconds before you feel cool air?
 

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Do you hear the blower motor running at the same speed while you sit at the light? Have you checked your alternator belt tention and the voltage lately? Heated windshield, main heater and heated driver's seat would drop the voltage down to below 12 volts at idling. I think that might affect the air temp door solenoid. The quick check if there's voltage drop is turning your wipers on when idling. They would move noticeably slower than normal.
 

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I understand there is no valve that controls coolant flow to heater core, so there is nothing that is stopping the coolant to flow and output warm air. Is it possible that water pump is kicking on only when the car is in motion?
Can't think of any other reason. Do you notice an abrupt change in air temp when you come to a stop or does it take few seconds before you feel cool air?
Within 30 seconds it will go from hot air to warm to cold.
 

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Do you hear the blower motor running at the same speed while you sit at the light? Have you checked your alternator belt tention and the voltage lately? Heated windshield, main heater and heated driver's seat would drop the voltage down to below 12 volts at idling. I think that might affect the air temp door solenoid. The quick check if there's voltage drop is turning your wipers on when idling. They would move noticeably slower than normal.
There is a slight drop in speed, but from what the service manager tells me the MDX is designed to conserve energy so when the car comes to a stop it would be normal for the temp to drop a couple of degrees. Problem is it blows cold air not warm. No issue with alternator, full diagnostic was done. At this point my lease is up at the end of the month, Acura has been no help so I will be returning the vehicle and moving on.
 
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