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Topic: Air out of dash ducts when moving (Read 635 times) previous topic - next topic

Air out of dash ducts when moving

How do I close the fresh air ducts on the evaporator/heater coil housing to stop outside air from comming in through dash vents at hiway speed?
91 GV U300 Unihome 40' Build 3811
6V92TA Detroit

Re: Air out of dash ducts when moving

Reply #1 –
Stump, we may have completely different air boxes, but when I opened up my 99's, I found that the "door seals" on the air box had degraded. They were made of a foam rubber and over the years had just turned to mush. Not wanting to completely disassemble that part of the bus, I just buttoned it back up. Hopefully yours will just be a stuck or defective actuator.
Len and Deb Speiser
1999 U270 36'
2017 Jeep Wrangler Unlimited
You're either on the bus, or you're off the bus!--Ken Kesey
If you're lucky enough to live in a bus, you're lucky enough!

Re: Air out of dash ducts when moving

Reply #3 –
GOOD THING HE DUCT, IT MIGHT HAVE BEANED HIM! 
Len and Deb Speiser
1999 U270 36'
2017 Jeep Wrangler Unlimited
You're either on the bus, or you're off the bus!--Ken Kesey
If you're lucky enough to live in a bus, you're lucky enough!

Re: Air out of dash ducts when moving

Reply #4 –
Here's two things I would check for:
1. Is there vacuum? 
The default with no vacuum is "fresh air" and directed to defrost vents but maybe some is leaking to dash vents too.  You should hear the vacuum pump run occasionally with ignition on but engine off.
2. Is the "fresh/recir" vacuum valve working?
Pushing the temperature slider all the way to left should engage the valve for "recirculate", pushing back on the other side of the detent it should move to "fresh".  With the dash top lifted you can see the mechanism that pushes the plunger on the vacuum valve.  With ignition on and engine off you should be able to hear the vacuum actuator moving - mostly through the recirculate air intake that is right in front of the passengers toes.  An oddity with our system is you can't get re-circulated warm air with this control system.
From what I remember about the flappers is there is no foam seal around them.  They are round with a smooth semi-hard rubber lip seal.
John Fitzgerald
1991 U300 (SAI) Side Aisle Island Bed 40'
Detroit 6V92 with Allison Retarder
Meridian (Boise), Idaho

Re: Air out of dash ducts when moving

Reply #5 –
They did change the box then. My 99 has a door with foam covering that makes it's own seal. Or, perhaps that is only the vent/defog flap. I had been expecting a smooth rubber seal and did not find one.
Len and Deb Speiser
1999 U270 36'
2017 Jeep Wrangler Unlimited
You're either on the bus, or you're off the bus!--Ken Kesey
If you're lucky enough to live in a bus, you're lucky enough!

Re: Air out of dash ducts when moving

Reply #6 –
Thanks,I unplugged the vacuum switch and the door vent door closed  My dash switch is not cutting off vacuum in recirculate mode,I'll leave it disconnected for max cool and heat.thanks
91 GV U300 Unihome 40' Build 3811
6V92TA Detroit

Re: Air out of dash ducts when moving

Reply #7 –
Quote from: JohnFitz –
Here's two things I would check for:
1. Is there vacuum? 
The default with no vacuum is "fresh air" and directed to defrost vents but maybe some is leaking to dash vents too.  You should hear the vacuum pump run occasionally with ignition on but engine off.
2. Is the "fresh/recir" vacuum valve working?
Pushing the temperature slider all the way to left should engage the valve for "recirculate", pushing back on the other side of the detent it should move to "fresh".  With the dash top lifted you can see the mechanism that pushes the plunger on the vacuum valve.  With ignition on and engine off you should be able to hear the vacuum actuator moving - mostly through the recirculate air intake that is right in front of the passengers toes.  An oddity with our system is you can't get re-circulated warm air with this control system.
From what I remember about the flappers is there is no foam seal around them.  They are round with a smooth semi-hard rubber lip seal.

John,

Thanks for the explanation of the fresh air/ recirculate valve and the other components of how my dash air works. I have a Fridgi-Cool and I believe it is working as designed except for one problem.  I checked it out and I can hear the pump go on and off for the vacuum needed for the vents to change direction of the air flow.  In front of the big box I noticed the plastic part that holds the drain hose and vacuum pump needed to open and close the big door for fresh air/recirculate was deteriorated and broken and the door is stuck in the closed position. Any ideas on how to loosen that door up and reattach the pump?  I thought about a piece of sheet metal or JB Weld but it looks like the whole box would have to be replaced to fix it.  It looked like someone had used fiberglass to repair it once before.  I may have to live with it or replace the whole box.

Jerry
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Jerry and Cindy Maddux
1993 U300/36WTBI DD6v92TA
build 4271  "Miss Lou"
1995 suzuki sidekick 4x4 toad
Gulfport, Ms

"Pride of Ownership"

Re: Air out of dash ducts when moving

Reply #8 –
Jerry,
The broken plastic housing appears to be just a cover for the most part.  It doesn't appear that any coolant or refrigerant lines would have to be disconnected to pull it off.  I think I found a replacement cover on the internet.  $181 for just the cover.  It sure looks like the same thing.  I suppose you could try to fabricate a fix depending on how handy you are but if the whole cover has become brittle it could be a loosing battle.
Let us know what you discover.  I have a heater core I need to replace some day.
Here's the link to the new cover that I think is the right one: Plastic Cover 060-00258 - SCS & VCS
John Fitzgerald
1991 U300 (SAI) Side Aisle Island Bed 40'
Detroit 6V92 with Allison Retarder
Meridian (Boise), Idaho

Re: Air out of dash ducts when moving

Reply #9 –
John,

Many thanks for finding what looks like a replacement cover that could work!  From the photos it looks like a good fit for the Fridgi-Cool.  The vacuum pump mounts in the center and the condensation drain is right under it. The old plastic just gave way on mine due to the stress caused by the pump and accumulation of water and rust over time.  I'll have to get in there to try and take the old one off first even if I could fabricate something.  I could then measure it to see if it would fit and clean up the rust and "un-stick" the door mechanism. 

The trick is getting in that space to do it. I'll have to take the left front headlight mount off to allow better access.  I really didn't want to have to disconnect any lines.  Hopefully just remove the caulking around the lines, take the screws out and remove.  I'll bet this is one area that gets overlooked for maintenance until there's a problem.  We all know what damage water can do to an A/C system if the condensation doesn't drain properly. 

It's a not a major problem except the fresh air/recirc door doesn't work.  I'll keep you posted with pics if I can make any progress. 

Jerry
The selected media item is not currently available.
Jerry and Cindy Maddux
1993 U300/36WTBI DD6v92TA
build 4271  "Miss Lou"
1995 suzuki sidekick 4x4 toad
Gulfport, Ms

"Pride of Ownership"