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Discussion Starter #1
Had occasion today to discuss an old / intermittent issue -- taking my truck to Houston tomorrow, so I need to know what to look for in preventing recurrence.
This problem only occurs when I drive in hot weather in high humidity. Truck does shift all A/C flow to defrost under load. I don't think that's related, though.
Repeated efforts to locate / fix any sort of avenue for water intrusion into the cabin have been unsuccessful, but the drain has been cleaned 3 times, the screen's ok,
& this did not stop the flooding.

Question: what kind of material would make a good wrap / insulator for the inside-the-cabin below-the-dash AC/heater housing, in case that really is sweating
enough to flood my floorboard?


In high humidity my AC causes a flood condition in the passenger side floorboard of my 1997 Ram 1500 Extended Cab. Truck is 318 auto 4x2 with all the toys
except leather seats. (Which reminds me: where would I find a replacement for the bezel for the electric seat controls? the existing plate will no longer hold in
place with the provided screws.)
 

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I don't think it is possible to flood the interior from condensation on the A/C housing. If it were that, you could easily see the condensation by looking under the dash when the problem is occurring.

I think there has to be an issue with the drain through the firewall. I know you said you had cleaned it 3 times, but that's the only place to get a good volume of water coming in from the A/C, unless there is a crack developed somewhere.

Is the rubber tube on the firewall in place to direct the water downward? If not, air pressure could be forcing the drain water back in.

I have no idea if this has any bearing on your truck, but my '06 Stratus had a flooding problem which was caused by improper design of the drain. My problem was that the drain went through the firewall into a rubber tube that was attached to the firewall. Water would back up in the tube because the hard plastic tube from the housing did not form a seal in the rubber drain. Water then filled the rubber tube and entered the passenger compartment through the foam soundproofing around the drain, so in hot, humid weather I had the same flooding problem. Chrysler had a tsb for a fix, which ImperialCrown kindly sent me, but what I did was to remove the rubber drain entirely, and use rtv to seal the opening where the drain comes through the firewall.
Then, to direct the water down and out, I attached a 1/2" pvc street elbow to the drain, and then used 5/8" id plastic tubing down to the bottom of the firewall.
 

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I believe that it's possible. If it weren't, home air conditioners and car air conditioners wouldn't have condensate pans and drains.

My Chrysler Cordoba has the unit as one piece completely inside of the passenger compartment short of a little drain that sticks forward out the firewall and turns down.

My '82 Crew Cab appears to have a split cover, and I wonder if the split goes through the condensate pan or sump or whatever it's called. I don't know about the later trucks, but if there's a gasket at the bottom where the parts of the unit go through the firewall, if that gasket is bad then I could see some kind of draining occurring, even if everything else is working.

I do not know, short of a fairly thorough disassembly, if there's a way to check this.
 

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Discussion Starter #4
I will watch it very carefully and probably minimize use of the AC to the extent possible this weekend.

Can't remember the name of the stuff the guy I was talking to said to use as a cover for the heater / AC box -- was thinking of trying Reflectix (tm).

I've never had a problem with this in low humidity; I live in Lubbock and often travel to Abilene / El Paso. It doesn't do this either place, or even in Dallas.
Houston, yeah. Not a problem on the way down, but on the way back home it began about an hour into the trip & the carpet soaked / sloshy by Temple.

Kentucky? It about washed me out of the pickup on the way home, altho I did not notice it going out there. We did spend a week in rain in that visit last
May -- came home the day after the Joplin tornado.

Also, this truck absolutely loves arid conditions.
 

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The 'L'-shaped rubber drain hose 'downspout' extension is important. If the hose piece is missing and the vehicle travels at higher road speeds for an extended period, the higher air pressure in the engine compartment can actually force the condensate back into the lower air pressure cab/HVAC housing.
You can also seal the firewall hole where the condensate drain exits the cab. Wet carpets will stink.
 

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For the vent problem, the vac canister that plugs into the power brake booster is shot. as for the floor flooding, I first would check for anything blocking the drain, I had this problem many times in my old 90 Spirit, chipmunks would put seeds in the drain tube clogging it, rust will do the same thing.


Tom
 

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I believe that it's possible. If it weren't, home air conditioners and car air conditioners wouldn't have condensate pans and drains.
Yes, the condensate is what causes the flooding. What I was referring to was his comment that it could be condensate forming on the outside of the hvac box under the dash. That would not accumulate enough volume of water in itself, if indeed any condensation occurred there at all.
 

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Discussion Starter #8
Back from the trip to Houston. Can report we didn't have flooding problems en route to Houston / Galveston. Didn't get much condensation on the box, if any.

Weather going down was high overcast, temps in the 65-70 F range. Didn't use much A/C.

En route home, carpeting under the top mat was somewhat damp at Gatesville (previous trip, by Gatesville the floor was sloshing) -- however Houston was
unseasonably cool. We were there Friday night, all day Saturday (full disclosure: driving Saturday was
 

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Curious - When you say the vent drain tube is clear, and the vent screen is clear, I think you are referring to the cowl air intake below the windshield, and it's associated drains on each side of the cowl, and maybe one in the middle, not sure about that. The A/C drain is a different animal, on the firewall directly in front of the heater box under the dash.
If you run water through the vents by the wiper arms, and you see water coming out, those drains are NOT the A/C drain.
The symptoms you are describing are those of a partially plugged A/C drain.
 

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Discussion Starter #10
The drain to which I refer is located under the hood on the firewall below the AC condenser.
 

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Perhaps you mean the evaporator. The condenser is the unit just in front of the radiator. The evaporator is the unit inside the car behind the dash.

When you run the A/C, you should see water dripping out that drain steadily and puddling under the vehicle. If not, the drain is probably plugged.
 

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Discussion Starter #12
What I mean is the canister mounted to the firewall in front of the passenger side, out under the hood, not inside the heater A/C box under my dash.
I've been helping a friend find/fix an AC problem and have handled five different condensers in the last 12 days, so I think I type that word by reflex....
On a 1999 truck (not mine) the proper AC condenser must be ordered by VIN number 'cause the "universal fit" ones *don't*.

There is the usual drip / stream of water if my truck is sitting with the A/C on and puddle underneath if it's parked after running the A/C. I am at a loss, here,
for what might be going on.
 

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OK, so maybe the drain is not plugged, but the pan under the evaporator has rotted, so that some goes out the drain and some drips out of the pan into the interior.

Or, the foam seal of the heater box is so badly deteriorated that there is a huge air leak here, and cold air leaking out of the box is causing condensation behind the dash, and it drips onto the carpet.
 

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Discussion Starter #14
So, I gotta take out the box to find the problem. OK. Just ... not today. This weekend, probably.
 

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Maybe not remove it - you might be able to remove the glovebox and idle the truck with the A/C on, and see if there is condensation, or get your hand near the box to see if the seams are leaking air.
 

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Discussion Starter #16
Well, that's why I was thinking this weekend: I will have trained adult help available then.
Things go so much better when I'm not trying to do this stuff without that.

It's not that there are fewer words said or wrenches bent. It's just that the results include fewer leftover parts,
bloodied knuckles, etc.
 

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You can probably get a good idea of what is happening by removing the carpet from the passenger side while you are troubleshooting. You probably can then see any dripping/leaking spots easier. The carpet will have to come out to dry the backing anyhow.
In my car, there is foam sound deadening sandwiched between the box and firewall, and going down into the footwell. If your truck has that, it absorbs a lot of water. Just cut it out with a utility knife and set it outside to dry. When it is time to reinstall, stick it to the floorpan with some rtv, then use duct tape on the cut seam to hold in place until the rtv dries.
 

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It would help to pull the carpet and padding away from the firewall and do a water test first to visually confirm where the water leak is actually coming from. Is it more after a rain or after using the A/C during humid weather?
A garden hose on low stream directed into the cowl and then the HVAC fresh air intake while a helper is watching inside the vehicle will help confirm where the leak is coming from. Cowl or HVAC? Diagnose first.
I really would hate to R&R a HVAC housing and still have the same problem.
 

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Discussion Starter #19
Thank you all. Yes, I'd hate to pull the housing only to have the problem recur. Heavy humidity during HVAC actual usage is the trigger. Several days in such an environment does aggravate the problem.
 

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Discussion Starter #20
Now, I need to get some part numbers. The firewall canister drain downtube, and the associated foam grommet, need to be replaced.
 
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