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NEED HELP Smoke from Dash Vents

Discussion in 'Technical Discussion' started by $ Khalid ! 9130, Oct 23, 2016.

  1. $ Khalid ! 9130

    $ Khalid ! 9130 Well-Known Member

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    Hey everyone. Been looking around about this for a while. Can't find anything good anywhere on this so I thought I would post here.

    This has been a problem for quite a while now. Usually when my Dads Yukon Denali is idle or stopped you can see smoke coming out from the dash vents. The A/C cools fine and everything, and the smoke goes away once the car starts moving again. There is no smell of any sorts either.

    I am guessing this is condensation?!?!

    Any ideas on how to take care of this. Although it is not a big problem atleast I don't think it is I would like to fix this.

    Thanks
     
  2. Blckshdw

    Blckshdw Moderator

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    Condensation would be water on the surface of something. When you can see the smoke coming from the vents, have you guys popped the hood and see if there's smoke under there as well? Maybe you can see where it's coming from to give you a clue where to troubleshoot next.
     
  3. Wooluf1952

    Wooluf1952 Well-Known Member

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    Does the air from the AC get warmer when stopped? I've noticed when driving at night when it's cooler, if I turn off the AC I some times have smoke (fog) come up through the vents. I believe it's from the damp air passing through the AC before it warms. That cools the air enough to turn it to fog, but not condense enough to turn it into droplets and fall out of the air. I hope that makes sense.
    My point being, you may not be cooling enough at idle when stopped. Does the smoke go away if you just increase the RPMs without moving?
     
    Redbeard likes this.
  4. TollKeeper

    TollKeeper Well-Known Member

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    It's nothing to worry about. It's moisture in the air that condenses slightly when going thru the temp change. The natural positive air pressure of a moving vehicle makes it so you can't see it when stopped.
     
    Redbeard likes this.
  5. MRRSM

    MRRSM Gold Supporter

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    The technical run down on this problem begins and ends with a Low Charge of Refrigerant. Now as strange as it may seem given all that Cold Fog Blowing out of the Air Vents... Here is what is actually happening ...and WHY:

    When the System Charge of R-134A drops below a level in which a sufficient amount of Refrigerant Vapour is available as a Super-Heated gas to be compressed by the A/C Compressor... Low Vapour Charge is then propelled through the Condensing Coils which causes the Vapour to change state from a Gas into a Liquid and give up all of its collected heat but suffers from what is called a Premature Vapour Expansion "FLASH-OVER" because an insufficient mass of Liquid Refrigerant is present to completely fill up the Liquid Line.

    Normally... the Liquid Refrigerant follows the Liquid Line into either a Fixed Orifice Tube or a TXV (Thermostatic Expansion Valve that is normally NOT stuck OPEN) and thence... into a series of Small Expansion Tubes, This action should happen GRADUALLY enough to allow the Liquid to expand into a Gas incrementally... in way that normally drops the temperature of the Evaporator Coils down to around 40-45 Degrees Fahrenheit. However... in the case of a Low Refrigerant Charge "FLASH-OVER"... the expansion happens so suddenly and prematurely... that it will Drop the Temperature of the Evaporator Coils down below the Freezing Point of Water at 32 Degrees Fahrenheit. It is the normal condition of the Evaporator Coils to be cold...cold enough to allow Moisture in the Air Column to condense and fall down into the Condensate Drain as Liquid Water. But if that Moisture FREEZES... ICING The Evaporator is inevitable.

    When this happens... all of that Warm, Moisture Laden Cabin Air being blown over the Evaporator Coils will very quickly Freeze any Moisture being carried in that column of air passing through and portions of the Evaporator Coils will Freeze SOLID and become blocked with whatever moisture there is to be present inside the closed cabin of the vehicle.

    If you have ever opened your Freezer Door and seen a similar "Cloud of Cold Fog" forming... or perhaps had a Fresh, Ice Cold Soda on a Hot Summer's Day... and allowed your breath to pass over the Ice Cubes settled in the top of the Glass and seen the same Water Vapour in your exhaled air condense over the Cubes and form a Small Cloud.... the exact same thing is what is happening under your dashboard. So If you left the Car-SUV Door standing open long enough while watching this "Cloud" of moist air blowing out of the AC Vents... eventually it will STOP as soon as enough moisture has passed over the Evaporator Coils to Freeze it up into a Solid Block of Ice. The result will be that the interior of the cabin will become uncomfortably warm until the Ice collected on the Evaporator melts and the whole cycle repeats itself:

    THIS is what the condition looks like...and while this Evaporator Coil is inside of a Residential Air Handler Evaporator Section... (The Home Interior Temps were in the 90's !) THIS is the common outcome of having a Low Refrigerant Charge in the System ...and all of the aforesaid Thermodynamics still apply:
    [​IMG]

    Back in the Day...when Detroit made cars with AC Systems that provided Mechanics with an Easy to Diagnose Tool to determine if the refrigerant was LOW and WET due to moisture being present inside of the system... A "Sight Glass" was usually positioned along the edge of the Fender Well mated to the Liquid Line as it exited the Condenser Coils. This "Sight Glass" was a sturdy, leak-proof High Pressure Resistant Mineral Quartz Lens that allowed for seeing any "Bubbles in the Stream" and some had a centred coloured Dot that would show Yellow if any Moisture was present in the Liquid Refrigerant Stream... or remain a Pale Green Dot if the system was de-hydrated with no invasion of damp, residual air in the lines.

    The "cool" part (pun intended here... ) was that if you could see a mass of Tiny Gas Bubbles flowing towards the Orifice Tube or TXV... then you would know to add Freon (Back then it was the now BANNED CFC --> R-12) and gradually add small increments until the system cycled "Bubble Free". Here are some images of the ones used in Commercial and Residential Split AC Systems and those with Heat Pumps, as well. This device is usually connected just Downstream of the Liquid Line Filter exiting the Compressor Pump Unit and as close to the King Service Valve as possible... while either a single or bi-directional Filter-Drier (for HPs) is installed in the Attic Air Handler... as close as possible upstream of the Orifice Tube or TVX at the Evaporator Coil to ensure only cleaned and desiccated Refrigerant is allowed to enter the Evaporator Coils:

    If I pulled a vacuum on a system with this device installed after filling up the system with Dry Nitrogen for about an hour or so... the Moisture Indicator "DOT" would change colour from Yellow to Pale Green... and be Good To Go.
    DSC07442.jpg DSC07443.jpg
     
    Last edited: Oct 23, 2016
  6. $ Khalid ! 9130

    $ Khalid ! 9130 Well-Known Member

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    First of all I would like to thank everyone for their input especially @MRRSM for this lovely reading material which I will have to go through a few more times to understand it :book:.

    @Blckshdw I will check it next time I have the car with me and post back

    I am not sure if it gets warmer. Because the car is usually cool enough for me to notice. So far turning the A/C off has no smoke from it yet. I will have to check once again if the smoke goes away by revving at idle.

    AGAIN A BIG THANK YOU TO EVERYONE :grouphug:
     
  7. MRRSM

    MRRSM Gold Supporter

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    LOL ... Forgive me @$ Khalid ! 9130 ...I should have used a visual media method for describing all of this technical stuff... I think THIS Video does a better job than my tome does:

     
  8. littleblazer

    littleblazer Gold Supporter

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    I Wouldn't worry about it until it starts shooting ice cubes at you.

    It's just a little bit of moisture. It's hardly noticeable correct?
     
    xavierny25 likes this.
  9. $ Khalid ! 9130

    $ Khalid ! 9130 Well-Known Member

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    Oh I loved the reading as well. It just makes me smile when I see these loongg detailed posts even for the smallest of issues. GMTNation for ever !!!

    Yep, but my Dads been like why suddenly now. We have had the car for quite some time now, hence the assumption that there is something wrong :2thumbsup:
     

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