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Thread: HVAC heat blows warm/hot on drivers side, cool/cold passenger side (warranty issue)

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    Administrator Daox's Avatar
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    HVAC heat blows warm/hot on drivers side, cool/cold passenger side (warranty issue)

    For those of you following my garage thread for Swarthy, you know that I have a bit of a HVAC heat issue. I get warm / hot air out of the driver's side vents, but cool or cold air out of the passenger side vents.

    I noticed the issue on the 2 hour drive home from getting the car. The car simply did not get overly warm in the cabin. On the test drive everything seemed okay. Spork also confirmed this as she went with me to get the car.

    On this morning's trip in to work, I did a bit more testing of this. I found out that it simply does not blow hot air with the fan blasting. It does blow warm, but not hot. This is despite the engine coolant being fully up to temperature (180F+). The driver's side is a lot warmer than the passenger side, but still not as hot as it should be IMO. It is noticeably cooler than any other car I've owned.

    I also tested the temperature out of not only the normal vents, but the defroster vent and also the floor / feet vents. The same thing happens. The driver's side blows much warmer air than the passenger side.

    I had a suggestion from Eggman to check to see if the cabin air filter was at fault. I did this and noticed it had probably never been changed. I cleaned it up as best I could and reinstalled it into the car. It definitely was dirty and needs replacing, but it is not fully clogged at all. Unfortunately, cleaning the filter out did nothing to fix the issue.





    At this point, I am thinking I have a busted flapper door, a bad stepper motor that isn't actuating a flapper door properly, or something is jammed in there stopping a flapper door from shutting correctly. It seems like some or a lot of cold air is coming in and mixing with the heated air from the heater core. I'm not sure why most of the cold air is going to the passenger side, but that seems to be the case. I'll be looking through the service manual to see what needs to be taken apart to start getting to the bottom of this. Any info, tips, or ideas are quite welcome!


    Custom Mirage products: Cruise control kit, Glove box light, MAF sensor housing
    Current project: Developing a rear sway bar alternative

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 41.7 mpg (US) ... 17.7 km/L ... 5.6 L/100 km ... 50.0 mpg (Imp)


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    Administrator Daox's Avatar
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    Just talked with my boss at work who does a lot of car work. He said someone he knows with a 2013 Jeep with ~100k miles (somewhat similar to my 2014 with 77k) had the same issue. It ended up being the heater core being plugged. They flushed it and everything went back to normal.

    That also would make sense in this instance. If the inlet is on the driver's side, it gets all the heat. By the time the coolant gets to the passenger side its already cooled off. One more possibility to check!

    Ironically, it wouldn't be the first time I flushed a heater core over Christmas vacation. Two years ago I did the same thing to my Chevy Metro.



    Custom Mirage products: Cruise control kit, Glove box light, MAF sensor housing
    Current project: Developing a rear sway bar alternative

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 41.7 mpg (US) ... 17.7 km/L ... 5.6 L/100 km ... 50.0 mpg (Imp)


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    Senior Member MightyMirageMpg's Avatar
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    Have you Check to see the heater core is actually getting hot? There's a vacuum valve inside the car that i don't think is monitored.

    The flapper actuators all have positional feedback, so 9/10 you Would Have a code unless the doors itself is messed up

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    Senior Member Top_Fuel's Avatar
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    Just a random tip regarding heater core flushing...

    If you can isolate the heater core, drain it and fill it up with a product like CLR. Let it sit overnight...and then flush it. A local shop owner told me he fixes most clogged heater cores with this trick.

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 51.4 mpg (US) ... 21.8 km/L ... 4.6 L/100 km ... 61.7 mpg (Imp)


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    Senior Member Cobrajet's Avatar
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    There should be a couple hoses going into your heater core through the firewall, as shown in your pics. With the car fully up to temp, put your hand on each of the hoses. If one is hot and the other is cold/cool, then it is a plugged heater core.

    If both are hot, then coolant is circulating through the core and your problem lies elsewhere. We have had a couple reports of heater cores leaking, but no plugged ones yet.

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    Senior Member Top_Fuel's Avatar
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    Quote Originally Posted by Cobrajet View Post
    There should be a couple hoses going into your heater core through the firewall...
    They're right in the center of the firewall behind the engine. Removing your air cleaner would make them easier to access...

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        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 51.4 mpg (US) ... 21.8 km/L ... 4.6 L/100 km ... 61.7 mpg (Imp)


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    Administrator Daox's Avatar
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    Thanks guys. I'll check out the heater core hose when I get home tonight.
    Custom Mirage products: Cruise control kit, Glove box light, MAF sensor housing
    Current project: Developing a rear sway bar alternative

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 41.7 mpg (US) ... 17.7 km/L ... 5.6 L/100 km ... 50.0 mpg (Imp)


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    Senior Member Top_Fuel's Avatar
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    Looking at the ductwork diagrams in the service manual, it's hard to imagine a situation involving mode/blend doors where hot air goes to one side of the dash...while cold air goes to the other side. As far as I can tell from the diagrams, the door to the instrument panel vents is either open or closed. But I will have to admit that the service manual isn't very good on this kind of thing for the Mirage.

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    I would borrow/buy a pyrometer and measure the inlet/outlet temps of the metal heater core tubes when the car is at full operating temperature...

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    By the way...how do you know your actual coolant temperature? Do you have a Scangauge or something similar? I'm just curious.

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 51.4 mpg (US) ... 21.8 km/L ... 4.6 L/100 km ... 61.7 mpg (Imp)


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    Administrator Daox's Avatar
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    Yep, I have a scangauge II that I measure coolant temp with.

    I did test the coolant temp on the hoses last night. I got home with a fully hot engine. I turned the heater to max hot, and max fan. I didn't measure it with a laser thermometer, but I did it with my hand. One was noticeably warmer than the other. The difference was not gigantic, but definitely noticeable.

    This makes sense to me if the end of the heater core is plugged up, the hot coolant will only cycle through the first half of the heater core. Well, the first half is the driver's side of the core!

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    Here is a pic of an actual Mirage heater core.

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    Looking at this diagram, you can see that the inlet and outlet are on the driver's side. The heater core is #7.

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    Thankfully, in the event that the flush doesn't work. A replacement heater core really isn't that expensive at all. PartsGeek has them for $66. Not that I want to tear apart the dash though!

    https://www.partsgeek.com/gbproducts...ad=47433949812
    Custom Mirage products: Cruise control kit, Glove box light, MAF sensor housing
    Current project: Developing a rear sway bar alternative

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 41.7 mpg (US) ... 17.7 km/L ... 5.6 L/100 km ... 50.0 mpg (Imp)


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    Senior Member Top_Fuel's Avatar
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    When I get home tonight (and the coolant is at 195 degrees+), I will shoot my heater core tubes with a pyrometer and let you know what the temps are. Might be interesting to see.


        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 51.4 mpg (US) ... 21.8 km/L ... 4.6 L/100 km ... 61.7 mpg (Imp)


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