Totally stupid question on water in vehicle HVAC ducts
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Thread: Totally stupid question on water in vehicle HVAC ducts

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    Totally stupid question on water in vehicle HVAC ducts

    This question is mainly about cars but it should apply equally to trucks. Ready?

    You know how almost all vehicles have a grill on the cowling that is at the bottom of the windshield around the wipers? The rather large holes in these grill works allows a lot of random debris AND WATER to just pour down in there.

    Where does the water go? During a torrential downpour or even in a car wash a tremendous amount of water goes down these vents. I assume the water and debris makes it down into the duct work for the HVAC. Is that correct?

    Does the water that gets into the HVAC ducts exit out the same drain hole used for the air conditioning condenser?

    See, I warned you it was a stupid question.
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    Quote Originally Posted by jgayman View Post
    This question is mainly about cars but it should apply equally to trucks. Ready?

    You know how almost all vehicles have a grill on the cowling that is at the bottom of the windshield around the wipers? The rather large holes in these grill works allows a lot of random debris AND WATER to just pour down in there.

    Where does the water go? During a torrential downpour or even in a car wash a tremendous amount of water goes down these vents. I assume the water and debris makes it down into the duct work for the HVAC. Is that correct?

    Does the water that gets into the HVAC ducts exit out the same drain hole used for the air conditioning condenser?

    See, I warned you it was a stupid question.

    I guess you could test your theory by locating the ac drain hose and dump some water out of a bucket and observe where the water is running to and watch the hose for drainage. Might work better with two people, one to dump and the other to watch. An open end water hose would probably work better than a bucket. That way you could target one spot at a time.
    Last edited by jimmylh; 07-28-2019 at 01:43 PM.
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    Depends on the vehicle.

    78 ford truck for instance has drain holes on each side that dump the water out near fender.

    Can mice crawl in these drains and into heater and cab.....YES on a truck with No AC.
    Leave Heater controls in "off" and "cold" positions.
    Close outside air "vents" on trucks with No AC.
    Trucks with AC do not have these vents.

    Another example

    Suzuki Samurai..Horrible design. Water leaves whatever dumps on top of heater core when Drains become clogged.Drains vent through firewall with little flaps over the outlets. Major job to R&R heater= about 12 hrs to get it out and clean it out.
    Solution= drill a couple 1" holes above heater core to vacume leaves out and feed hose in to wash dirt out of core.
    Mice can't get through this system...they chew hole through rag top instead.

    07 4Runner
    Not sure where water goes but mice will chew through cab filter behind glove box = nest in glove box.
    Fix..buy new filter..install SS gutter screen or similar on input side of filter.

    This is a know problem with many toyotas...prius being one of them...No I don't own a prius & never will.
    Last edited by theduke; 07-28-2019 at 01:55 PM.
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    Dan


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    The vents are air inductions not related to engine aire intake. Like you said, there for cab air intake. Pretty sure theres a fatter rubber hose drain which tapers into a slit on many vehicles. Its in the engine bay on the firewalls. At least i know this is what my old 92 jeep wrangler has. Every once in a while i would need to squeeze the bottom of it open and drain out some trapped water and gooky debree.


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    The exact details will depend on the vehicle. The cowl air intake typically has its own drain hole(s) immediately beneath the opening intake, typically on each side of the car. The AC evaporator and heater core are typically housed in an enclosure that is mounted on the interior side of the firewall. So it will have a drain port on the firewall side that will penetrate the firewall.

    The cowl intake duct is designed so the air intake is at a point to minimize water being introduced into the HVAC intake air. In a vehicle, the AC serves not only to provide cooling, but de-humidified air to assit in clearing fogged glass. It it why the AC compressor runs when the defroster function is selected. Introducing rain water from the cowl intake air would be counter productive. I often run my AC when drivng in rain conditions, even when the temperatures are cool, as it keeps the glass from fogging. It is amazing just how fast the AC will clear fogged glass.

    When I clean my vehicles, I always make a point to utilize the shop vac to clean the leaves and pine needles that collect on top of the cowl intake screen.
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    Thanks all for the feedback. I have a Toyota Highlander that about a year ago got a clogged AC drain and when that happens it gets a certain area of the carpet wet in the driver's foot well. It's a great design - not. The drain hose is over a foot long and crooked and comes out near the firewall about a foot in from the passenger front wheel. The only way to clear it is to crawl way underneath and blow up into it with an air gun. Which I did and then water ran out for about 30-seconds.

    All as been well since and a few days ago I noticed the same spot wet again. So I pulled the car on the level and was going to lay a sheet of cardboard underneath to see if water was draining. But before I could even get the cardboard in place I saw water dribbling out. I made several trips the next day and each time I would check my parking spot after sitting and there was always a small puddle of water. So I assume the drain is clear.

    I'm thinking that perhaps there is debris in there causing the drain to temporarily get blocked and that it somehow then clears itself. I see no other evidence of the roof, windshield or windows leaking.

    My previous vehicle had a little rubber flapper valve for the drain instead of a hose and it was mostly clog resistant.

    It seems that as long as there have been vehicles with AC there have been problems with clogged drains and wet carpets. One would think they would have a more resilient solution figured out by now.
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    on some vehicles the passenger can kick the hose loose from the AC unit or floor matts may kink it.

    Most are built with the "whole" drain system out side the passenger compartment.

    Can you unhook it inside truck/car...blow it clean to the "outside"
    Perhaps stick a shop vac on outlet of AC box and suck out whateverelse .
    Dan


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    Quote Originally Posted by theduke View Post
    on some vehicles the passenger can kick the hose loose from the AC unit or floor matts may kink it.

    Most are built with the "whole" drain system out side the passenger compartment.

    Can you unhook it inside truck/car...blow it clean to the "outside"
    Perhaps stick a shop vac on outlet of AC box and suck out whateverelse .
    It appears to be clear now as water is running out consistently. I think the issue is debris in the AC duct work settles to the bottom where the drain hose is and blocks it. When you blow up in to clear it, it only temporarily moves the debris out of the way but it will eventually settle back and find it's way to the spot where the hose attaches. That's my theory anyway because I know the hose itself is clear.
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    Quote Originally Posted by jgayman View Post
    It appears to be clear now as water is running out consistently. I think the issue is debris in the AC duct work settles to the bottom where the drain hose is and blocks it. When you blow up in to clear it, it only temporarily moves the debris out of the way but it will eventually settle back and find it's way to the spot where the hose attaches. That's my theory anyway because I know the hose itself is clear.
    I wonder if you could squirt some foaming ac coil cleaner up there. It expands and will soften up leaves, dirt, bug crud, etc.
    Then flush with water.
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    Quote Originally Posted by arlen View Post
    I wonder if you could squirt some foaming ac coil cleaner up there. It expands and will soften up leaves, dirt, bug crud, etc.
    Then flush with water.
    Sounds like a nice idea.
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