Hot air coming in while moving and keeping cool

[neoneddy]

I've added another inverter (Victron in Parallel) which allowed me to run my 2 Coleman mach 3's no problem.  We  decided to head east to Wisconsin for a day trip,  as a small shakedown with all our new improvements.  We had both ACs running for a few hours before we left and in the heat and sun got the inside down to 75 or so,  it felt great inside.

Before you read this next bit, keep in mind I have the valve up by the driver turned off for heat and another in the engine bay that supplies water  to the heater core (is there a second?  I can't find it, I imagine it's a loop)


So we head out, I'm commenting to the Mrs about how nice this is, ride is quiet, nothing is squeaking or rattling ( one of the things I hate about most RVs) and then I start to notice every once and a while this feeling of warm humid air.   I can't quite figure out where it's coming from, could be the door, but then we settle on it coming from around where the old ramp was.  I've since framed over it, but there was a gap in between the drivers floor level and the passenger where that framing was, I put my hand down there felt the heat.   By the time we reached our destination it was 80 inside, no bear in mind we left around 6:30pm and didn't arrive until 8:30 or so, the sun was low and curtains drawn / most of this heat I'm convinced was from the engine one way or another.

To start I took off my covering over the old ramp area and filled it with fiberglass insulation and also put some under the next level down (with the air lines, etc) I believe this was an air return for the OTR HVAC system, so it makes some sense that heat could seep up, hopefully this stops it.   My door seals might not be in the best shape, last year I tried to put some aftermarket weather stripping on it and it wouldn't close properly, so  I took it off.

What are some other areas to look for?  And is there a second shutoff for the heater core?  Or could hot air be circulating all the way back from the engine up front and up through that bay even if it was off?

What don't I know that I don't know boys? (and gals if you're out there)

[DoubleEagle]

Yep, hot air rushing at the front of the bus will find its way in. Two A/C's on a hot summer day is not enough, you need three or more depending on your insulation and sealing levels. I know Eagles best, but I have driven many MC9's. Open the outside panel opposite the driver floor area, there you will see the hose connections to the heat valve on the inside. Make sure that the hot coolant is not getting there. The front dash area could have corrosion of the bulkhead and floor panels that has left holes for the hot air to come in, and there are fresh air vents that might have leaks, or be wide open even though you think they are closed. I have driven Eagles across Texas on super hot days with three 13,500 btu A/C's going full blast - same result as yours. The big entertainer coaches usually have five A/C's on top, and their doors are sealed well. The stars don't like to sweat. 

[neoneddy]

Ah well, I didn't want to go the route of 3+ roof ACs because then I'd almsot certainly have to run a big generator while driving and I've been wanting to avoid that for a number of reasons.

I'll pull that outside cover and maybe even the one inside in the bay to check for heat coming in.  I'll probably have to take it out again... uh just the worst :-)  Right now I love taking it out, we'll see how I feel about it after our trip to the Black Hills  and then Texas later this summer.

[Branderson]

Can you close a door to the bedroom and run two a/c's to cool the smaller area?  My recent trip I talked about on the other thread, we got to 80 degrees and I was confused b/c I've never gotten that warm.  I told her to close the door and it helped a little.  I was thinking oh great, another problem.  Then after awhile, I ask her, did you put it on low cool or high cool?  She said Low.  I bit my lip and told her to pls put it on high cool. 

[neoneddy]

You know, I don't recall what it was set at, maybe they were on low.   I insulated the snot out of the back to protect against heat and noise, not to say  it's not part of the problem.

Right now I have one ducted AC  and it runs the length  of the bus, it's nice in the evening to just run one up front and still get cool air in our bedroom.  The other is normal and spits out air from the unit only.   I'm planning to convert the both to ducted to hopefully pressurize the system more to really get the air moving.

[DoubleEagle]

Ah well, I didn't want to go the route of 3+ roof ACs because then I'd almsot certainly have to run a big generator while driving and I've been wanting to avoid that for a number of reasons.

I'll pull that outside cover and maybe even the one inside in the bay to check for heat coming in.  I'll probably have to take it out again... uh just the worst :-)  Right now I love taking it out, we'll see how I feel about it after our trip to the Black Hills  and then Texas later this summer.

I think you will feel very hot and sweaty about it. Try crossing the west at night, park in the shade (if possible) during the day, but then, do you have any generator now and are you dependent on being plugged in?

[richard5933]

Not sure how the MCI is set up, but in the nose of the GM buses there is a vent which was intended to bring fresh air into the bus. Our 4106 had this vent covered with sheet metal, but our current one has a damper that can open or close it. Is there such a thing in the front of an MCI?

Also, the factory OEM probably had fresh air intake(s) somewhere. On the GM they're on the sides. If these exist and are still in place, they could be forcing outside air into the bus when at speed.

Does your manual show what the original airflow pattern was with the factory HVAC system? If it doesn't my first step would be to be certain that all the possible intake routes are thoroughly closed.

[neoneddy]

@doubleeagle yeah that was a thought, I prefer driving at night anyway.

We have a small generator and almost 2000 watt of solar to boondock with, but we'll be at campgrounda for alot of our blackhills adventure.

@richard - I'll check for venting, thanks.

[Branderson]

I would much rather drive at night but I feel that my lights aren't that bright and I underestimated how much I like to see in the mirrors.  I'm wondering if I can get brighter lights that are just plug and play.  I think I can take my lights to Napa and see what can be replaced.

Sorry OP, I missed that you don't have AC units on the roof.  I guess closing a portion off inside wouldn't do much. 

[neoneddy]

@branderson , No I do have 2 units on the roof, but I have them ducted in the ceiling.

I have  set of these https://www.amazon.com/Rectangle-Headlights-Freightinger-Chevrolet-Oldsmobile/dp/B077NZKSJ6/ref=sr_1_1?ie=UTF8&qid=1529349466&sr=8-1&keywords=led+peterbilt+headlight

Normally only a small section of 1 set is on, when they switch to high beams it's like the sun.  https://youtu.be/wOKKGaRRp_w?t=615  Here is the video where I installed them.

[neoneddy]

I did some more looking and reading in the maintenance manual.  http://busrvparts.com/PDF_Files_MCI_9_Maint_Manual/MC-9-Maint_Manual_Section_16.pdf

The Air intake is sealed up with some rubbery / gummy stuff, on purpose it seems, not by me.

My door vents are covered by a decorative vinyl piece, I 'll need to look behind there soon anyway.  Then I noticed there is a bottom door exhaust, huh I'll need to close that up.  Then reading further " Approximately 20% of the conditioner air is fresh outside air.  This provides a healthy fresh atmosphere in the coach"  That was true with 40 passengers  and an AC system capable of making indoor ice, but not  now.   I'm so fighting a loosing battle here if it's 20% .  I'll start closing everything off and see where that gets me.

[chessie4905]

That ducting could be absorbing a great deal of heat from roof and ceiling. Check duct outlet temp. I can't see how you will be cool in hot weather with only two a/c's that are ducted in a 40 ft coach. What btu outputs are they and where are they located?

[neoneddy]

They are bout 10ft in from each end.

I also have most of the roof covered in solar so it's a built in shade.

Last I checked the outlets blew about 20 degrees cooler than ambient inside. I measured with a thermal gun.


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[solardude]

I am not as familiar with the MC9, but I would imagine it is close to the C3. With that said, the C3 has vents in the front of the bus, just above the bumper. Tiny slots that route to a 3 or 4 inch tube that leads to the return ramp. That is where the 20% fresh air would have to comes from. I think there is a dampener just before the air enters the return ramp area on the C3. Maybe on the MC9 as well. You should be able to access it all from the spare tire area.

Hopefully this helps.

IMHO, trying to seal off all the gaps will be a futile effort because when the bus is going down the road, there is a pressure differential (vacuum) on the interior of the bus. You would be ahead of the game to choose your point of air exchange so you can manage it.

SD

[Dave5Cs]

OP? b/c? means?