Where is the 86 F-150 Vent air entrance?

I have had a problem as long as I've owned this truck ( ~12 yrs ) that leaves and debris will make it's way into the air ventilation system. So as soon as I kick on the fan, small leaves will blow out usually on the passengers feet. I am sure that I am missing a screen or guard of some kind that is supposed to prevent this but I don't know where to start looking. I have examined the parts breakdown of the HVAC piping but it doesn't appear to highlight the external entrance of air into the system which is the only place the leaves could be coming from.

My best guess is in the top of the truck under the sheet metal just behind the back of the hood but I'd like some way to confirm that and then find steps to remove it. Just eyeing it over it looks like I'm into a big job to lift that sheet metal off to go 'hunting' for an entrance that might not be there.

Any guidance here would be much appreciated.

It does come in through that grille and it was a know issue resulting in a change in 1987 to a "pinhole" style. You can remove the grille carefully (lower windshield trim has to come off) and put some screen under it and reinstall the grille, works quite well and isn't really visible.

the best solution I have ever found for this was to clean out my garage

OK --- Thanks for the responses.
I was a little bemused to find that it was "supposed to work that way".

RE: Getting the grill sheet metal off:
I don't think the windshield trim has EVER been removed from this truck. I can tell by the many glass nicks and tiny green shoots that grow out of it every spring.

I have removed the blower fan in the engine bay and pulled out a small trashbags worth of leaves and debris sitting in the blower box and up against the AC evaporator. There is more in there I just cannot articulate my arms enough to get it all.

Also pull the resistor pack that's there beside the blower motor.  You can get more yuk out that way.

And, pull the kick panels.  That gives access to an area where a lot of the yuk has gone.  If you have the vents in the kick panels then pulling the vents gives access.  If you don't have the vents then there are blocking plates behind the kick panels and if you pull them you'll have access.

look up a story i wrote a few weeks back on here. cheech and chong in the title. it will make good sense to you given your current issue

mat in tn wrote

look up a story i wrote a few weeks back on here. cheech and chong in the title. it will make good sense to you given your current issue

Search: cheech and chong strike again [12/24/21]

archeman wrote

I have removed the blower fan in the engine bay and pulled out a small trashbags worth of leaves and debris sitting in the blower box and up against the AC evaporator. There is more in there I just cannot articulate my arms enough to get it all.

This is what your firewall looks like if you remove the big black heater/AC box.(Credit NC Dave for the pic!)



The tall vertical rectangular opening that is farthest to the left is how the leaves, dirt, debris get inside. The dirt travels along the cowl trough in front of the windshield, then falls down the passenger side and gets sucked into the hole, which by the way is right in front of your blower fan.

That cavity is deeper than the hole in the firewall, so there's a lot of room in there for dirt to collect and build up. As Gary mentioned above, if you pull the passenger side interior kick panel you can get in there with a shop vac and clean it out. You might have to stir up the Potpurri of leaves with a screwdriver to get everything loosened up.

At the bottom of that cavity is a rubber "duck bill" drain for the water (rain). Good idea to make sure it's clear and  free as well...you should be able to pour water in there and it will run out from behind the fender. They do get plugged up after 40 years;).

Here's the location of the "duck bill":

Well done, Cory!  

Hey those are great pics of the firewall and it really answers a lot of questions -- thank you.

I read the post Cheech & Chong and now I guess I should really tell the "Whole Story" here since that story was so close to the mark and completely explains how I got to investigating the flying leaves.

My son had a job interview and wanted to borrow my truck because his car died again. My truck hates this kid. If ever anything is going to go wrong with the truck it always happens to him, strangely never to me. I heard him start it up and then a few moments later (I assume he was looking at his phone) he starts hollering for me. I look out and see him running out of the cab with a line of smoke following him. It didn't take long to figure out that the issue was related to the fan motor but no fuses had blown. I sent him on his way with instructions to avoid the fan. He said he had to go to the interview smelling like a campfire.

I disconnected the blower fan and it would spin (no bound bearings) by hand but wouldn't come on when switched on. I replaced the blower motor and then noticed the debris in the blower box. That started me down the actual rabbit hole that is the ventilation system.

I saw the plugs that enter wall to the lower right of the blower motor but I didn't know what those were.
If I understand you correctly there is a high current resister on the other side that is prone to igniting warm fires to sit and watch your old truck burn down?

I'm sitting here reading this aloud to my wife. we are both laughing loudly. welcome to the club brother! yes, the plugs are on a resistor bank which holds four circuits. one without a resistor for high fan speed and three successive resistor coils, each slowing the fan a little more. they are specifically placed in front of the blower so that they are cooled by the air flow. there is also a small thermal fuse link there are as a safety in case of a fire or a stuck motor so that as the heat becomes excessive it will turn off the resistors. not resettable! if it blows then you need a new resistor assembly before the blower will work.
this problem is worse on trucks that have been neglected or even in storage too long . mice love to build in there

these two pics are from last summer. a customer inherited her dad's truck. an 86 sb, xlt, 4wd, with 5.8/c6.
 I love that truck!! anyway it came to me for carb service, water pump, and we did timing chain as a preventative, but it turned out to be long past due. phase one completed she wanted new air cond. that mice nest was what I discovered when I removed the old evaporator. pic worthy. I showed him and let him decide to show her. this is more common than I like to say. if you have one of these trucks. pull the blower and get your shop vac and clean it. if it turns out to be unneeded, good for you. and now enjoy the peace of mind.

Been there, done that, smelled like a camp fire!  Was taking my wife for a ride in my "new" 82 a few years ago.  Nice sunny day with temps in the 30's, but we needed a bit of heat.  Smelled someone burning leaves and then we realized there wasn't anyone w/in miles of us.  

So yes, welcome to the club.  Pull the resistor pack as there are obviously leaves around, if not in, it.  And pull the kick panels 'cause there will be debris in there that traps moisture and rusts things out.

let me tell you! the wonderful welcome to autumn smell of burning leaves in the distance is NOT the experience you get when you ignite a mouse nest. ooooooooooooooh nooooooooooooo! this one is different!

I need to clean out that in my Bronco. The air throughput has become so weak…

I have done it once before.. pesky mice!

I wanted to post a follow up on how vent system the clean-up is going.

Based on advice from Gary and Rembrant, I took out the passenger kick plate and opened that square access panel (about 6" X 10") and found many interesting discoveries.

1) Some lazy stereo installer had routed a new radio antenna through the top of this panel just clamping the panel back down on the cable. The leak from that isn't that much so I'll consider my options and figure out if I can put a proper access hole with grommet.

2) Looking through the access hole, I can see that the engine bay airbox isn't actually flush against the firewall. I can see light around the edge so that needs to be fixed. This problem appears to have been around probably since the truck was first assembled. There are two threaded bolts that extend from the plastic of the vent shroud and the bottom one was jammed into the sheet metal bending it near the hole and appears to have never had a nut put on. The top nut was there but when I put a socket on it and tried to tighten it just resulted in spinning without tightening. I asked my daughter to watch what I think was the other end of the bolt and she said it wasn't spinning on the engine bay side so maybe the bolt is broken in the plastic??? I was able to clean up the debris that was blocking the rubber drain at the bottom of the space.

 

3) At the bottom of the access space, I found this odd rubber cap or perhaps a plug filler of some kind. This thing probably used to be rubber, but it has zero elasticity any more. Feels like a burned potato chip now. I put it under hot water for a while and it did feel like it softened enough to get back into it's home if I knew where that was. Anybody know where this lost sheep belongs???

I'm confused, but what's new?

What you show in the picture looks like it is the opening through the firewall rather than through the kick panel plate.  Right?

If so, there's supposed to be a gasket between the firewall and the HVAC plenum.

As for the bolts, I'm trying to remember, but I think that some of those are threaded into the plastic of the plenum.  So if they spin you may need to replace them with a bolt and put a nut on it.

And the plug looks like one that is used in the cowl or on the firewall.  Look around, you may have one like it in place and in that case someone probably dropped one in your truck and didn't pick it up.  Maybe your truck was built on Monday or Friday?  

That big plastic plug fits on each side under the cowl.
I could not find a picture of them from my build.
Tomorrow I can get pictures from my parts truck cab as it is sitting out in the yard.
Dont know what I will do with it yet and why I have not scraped it yet.
Dave ----

Gary that picture above is me holding my phone inside the access panel and pointing it fwd to the firewall.

Without a light on (in the dark) you can see light from the engine bay shining around the seal, which means fumes and whatnot can also come right in the cabin and have been for years. I guess that is why I can't find my keys all the time! I knew it!

The rubber cap/plug thingy was sitting inside that space in the debris that was blocking the bottom drain.

Looking fwd to the pictures of where that plug came from and plugging it back up!