Any reason to NOT seal fresh air intake near heater?

[TheHubbardBus]

Hopefully you know what I'm talking about. On the driver's side feeding into the compartment where the heater is mounted is a fresh-air intake, with a sheet-metal flapper that opens & closes it, which is controlled by a dial knob (via a cable).

The source of the air can be seen in the first picture of the bus... right by the hood latch... the only thing still yellow. The second picture shows the driver-side structure that houses the heater (with switch panel on top). This opening/flapper is directly behind, and below, the blower fan shown in the picture (If you look real close you can see the cable that attaches to the top of it). The 'recirculating air / fresh air' knob in this picture controls it.

My question: Is there any good reason to not seal this up for good? Am I missing a purpose for this I'm not thinking of at the moment?

Seems to me that no matter what I do, this is prone to leaking air when I don't want it to. We have a maxx-fan, and a whole bunch of windows that can be opened any time we need air. And it draws 'fresh' air from right outside the diesel engine ().

[dbsoundman]

I'm curious about this too, I just realized this weekend when it was windy and COLD that air just flows right in from the outside if the defroster is set to "Fresh air", and even if it's not, I'm not sure it blocks much air coming in if the wind is stiff enough.

[Compass No Map]

Originally Posted by TheHubbardBus

And it draws 'fresh' air from right outside the diesel engine ().

As for the quote, the exhaust gases cannot enter the fresh air intake unless there is an exhaust leak at the engine, which would be immediately noticeable by the sounds as well as the smell.


In cars, the recirculating feature is intended only to heat/cool the interior of the car quicker by blocking the cold/hot air once the system is blowing the heated/cooled air. It is intended to be turned back to fresh air once the interior is at a comfortable temperature in order to prevent inside condensation on the windows. But you probably already knew this. In buses, it is the same thing. Yes, in the bus you can open any number of windows to do the same thing.


My thinking is that it would likely be better to make a plate that will fit over the inlet, held on with good magnets, to completely close it off from the outside when desired. I think if it were me, I would use two steel or even aluminum plates, one which would completely cover the whole and hold the magnets, the other would be just the right size to fit into the hole in order to act as a vertical support and would be glued to the back side of the outer plate (I would likely use JB Weld for this.)


However you do it, I think it might be better to make it a removable cover. I hope this helps.

[TheHubbardBus]

Thanks Compass! The reason I posted is because I was considering a 'permanent' solution, and wanted to make sure I wasn't having a brain fart before I did something irreversible.

As it is, I couldn't permanently close it if I wanted to (too tight/no clearance). I could have when I had that whole unit pulled out into the center of the bus, but at the time my plan was to get it working to the point it sealed up tight when closed. But the very nature of it precludes that effort IMO... I'm not confident it will seal up 100% airtight when closed no matter what I do, and I need it to.

I ended up running a thick bead of high-temp red silicone where the flapper mates with its recess. It was hard getting up in there, but ultimately doable (with heater removed). Then closed it fully (adjusting cable to make sure it was as tight as could be), pulled the knob off, and inspected to make sure there weren't any gaps. Then I ran another bead around the outer edge just to make sure.

So it's not permanent, but I don't see it opening again without the use of a utility knife.

[cadillackid]

its your defrost air intake.. close that up in the rain or in real cold weather and then you have stale stuffy crappy breath-smelling air to try and defrost the glass with!..



a maxx-air fan sucking air out of a vent in the back needs to make it up somewhere so instead of sucking in the cold air and running it over the heater.. you'll make up your lack of air by creating cold drafts inside the bus..



sealing it up in summer makes sense.. esp if you have air conditioning. and the bus manufacturers have that in mind as you can close the air intake and open it.. if that doesnt work then your mechanism is broken.. and instead of the seemingly skoolie way of "rip it out'' might try fixing it so it works right.. thats what I did with my busses and its nice being able to choose the outside air or not..



any air you suck out of the bus will get sucked in someplace else..

[TheHubbardBus]

Yep... that's the reason I posted. I knew I was missing something. And I knew I'd feel real stupid when I found out what that something was.

Time to whip out that utility knife. Thanks Christopher. I need you on speed-dial.

EDIT: Ok, at the risk of sounding obtuse, I still don't get it.
If I run the defroster, with that duct closed (or on recirculate), air is drawn from the cabin. But the defroster is putting it right back into the cabin. So I don't see how sealing it off would cause air to be drawn from outside via another route? Isn't it just doing exactly as advertised... recirculating the interior air?

Also, why / when is running cold air over the heater to heat it up better than using cabin air that's already (hopefully) warm?

EDIT2: Nevermind. I re-read the 'rain or really cold weather' bit. Then I realized stale air isn't necessarily a 10 minute inconvenience depending on your environment. Give me a break. I'm from the desert SW.

[cadillackid]

sealing up the vent wont cause cold drafts in oif itself.. someone mentioned they have a Maxx-air fan they could use for ventilation while driving.. at least thats how I read it.. the maxx-air fan sucks air out of the bus.. that air needs to be made up and brought in somewhere..



so instead of bringing it in the intake duct it will suck it in through anyplace it can.. only when the maxx-air fan is on (or its vent is opened creating a suction on the bus)..


a Maxx air fan on with the driver window open would clear the nasties and moisture out of the bus too.. but it also will be blowing whatever the outside air is (rain wind, perfect, cold, hot) right in on the driver too..



in sumer when its hot out and you have the A/C blasting then closing that vent makes sense (just like when you push recirc in your car).. the humidity and with it a lot of odors, etc are being removed by the A/C coils..

[TheHubbardBus]

I get it now, and as always, appreciate your input. I should have waited a couple days before acting on a question I just asked (have a bad habit of doing that). I honestly can't remember using the fresh-air intake on anything I drove... winter, summer, rain, shine. I asked Sharon and she says "Yeah, I've used it" with this look on her face like "What have you done now?"

Anyway, It's 2 PM here, I started at 9, and I've just gotten all the silicone off. Now it's time to get to work bending the flapper back to straight after inevitably tweaking it breaking my (incredibly strong) silicone gasket. I hope to get back to where I started by day's end (lol).

[cadillackid]

You always have the recirc button pressed on (lit up ) on all your cars? Even in winter? These are the guys you see driving around in rain / snow with windows so fogged you can’t see a thing. And usually smells like bad breath inside or BO.. lolol..

Recirc is off (fresh air on) is default in all cars. Cars without A/C don’t even have recirc..

In a car and in a bus the air is mixed. When the door is open to fresh it doesn’t close off inside air it just allows the fan to suck in on both the inside and outside vents.

In a car when you switch the defroster on the recirc mode is automatically turned off.. on a bus it’s all manual up to the driver. Except for some of the newer busses do it automatically.. Thomas C2 and the newer IC CE and bluebird visions

[TheHubbardBus]

LOL. Every bit of what you just wrote is 100% new to me

I figured recirc would be the default. Or perhaps more accurately, I never thought about it at all.

And yeah, I've been that guy. I figured God gave us two hands so one could clear a vision portal while the other held the wheel.

I don't know about the bad breath & BO bit, though. I only recirculate the finest fragrances.


FWIW the flapper is now 100% functional. The hard lessons are the ones that stick (like silicone).

[cadillackid]

Originally Posted by TheHubbardBus

LOL. Every bit of what you just wrote is 100% new to me

I figured recirc would be the default. Or perhaps more accurately, I never thought about it at all.

And yeah, I've been that guy. I figured God gave us two hands so one could clear a vision portal while the other held the wheel.

I don't know about the bad breath & BO bit, though. I only recirculate the finest fragrances.


FWIW the flapper is now 100% functional. The hard lessons are the ones that stick (like silicone).

LOL I climbed into more than one Uber and instantly downed the window because of the BO inside and the heater was on recirc!.. LOL..



luckily with Covid people are more aware of it and keep it on fresh and usually a window cracked no matter what for Uber / Lyft..



fortunately a bus is big enough that your whole family could prob each down a bag of white-castle sliders and not be able to fill it with Butt-Odor (if you know what white castles are)...

[TheHubbardBus]

Originally Posted by cadillackid

LOL I climbed into more than one Uber and instantly downed the window because of the BO inside and the heater was on recirc!.. LOL..

luckily with Covid people are more aware of it and keep it on fresh and usually a window cracked no matter what for Uber / Lyft..

@cadillackid... (NSFW)

https://www.youtube.com/watch?v=hVsj0_hSFRw

[Johnthebusboy]

Sealed mine. No problems.

[Ross]

White Castle mini burgers! Been a while. I completely agree with "fix the problem, don't just rip it out". I went through my heater unit and corrected every problem it had. Loose fan mounts, bent damper, leaky defrost ducting. Now it works perfectly. In the bus AND my cars, I always leave the heater/AC on fresh air, unless I get behind some old jalopy belching smoke, or some jackass rolling coal.

[TheHubbardBus]

Just to be clear, I wasn't attempting to half-a$$ anything It's not in my DNA. It was, in fact, an effort to seal the bus up better than it ever had been. It was just an ill-directed, not well-thought-out, attempt.

It's back to being completely functional, and now sealed up properly. This is one of those items where what works great for home insulation doesn't work great for vehicle respiration Compromise is not my strong suit, but I'm working on it.

[Booyah45828]

It's not the air, but the humidity in the air. That's what causes the interior of the windows to fog and what you want the defroster to get rid of. That's where the stinky/BO/bad breath air comes from. Being in AZ, I'm not surprised that you didn't know that. Living in the swamps of Ohio, you learn quick about too high of an interior humidity and the condensation/mustiness that comes from it.

On modern cars, when you select defrost, it automatically engages the ac and disables the recirculation mode. Old vehicles you'd have to select all that stuff manually, and therefore disable it manually. The reason recirc is disabled is because if you're getting interior condensation, the air on the outside is likely less humid then what's present inside. Fresh air in a vehicle is actually desirable, as it flushes out co2, co, and any other hazardous gases that could accumulate inside. FWIW I don't think any vehicle completely seals off the fresh air vent in recirc mode. They all still allow some(20% IIRC) to enter.

If your bus is going to be parked on blocks and left, seal that up, as it no longer serves a purpose. But if you'll be driving this at all, I'd fix it and leave it in place.