Dash Vents

[Georgia Mike]

I finally fixed my dash ac today. I found a small hole in the condenser and used a aluminum brazing rod to fix the hole. Vacuumed down and added 134a now its cooling good again. I have a problem with the dash vents not operating correctly. When I turn to max ac it should just come out the top main vents but it comes out of the floor vents as well. It seems to come out of all the vents at the same time. I can hear it trying to change but never seems to go all the way to just one item. When i turn to defrost i get some air but i still have it coming out of the floor and front vents. I checked in the front generator compartment and found that the vacuum pump is working. I pulled the tiny line at the bottom of the round ball storage tank and the pump kicks on then when i plug it back in it will run for 20 seconds then shut off. It seems that is working correctly so i assume the problem is under the dash. I have looked through the site and cant find much info on how it works under there. Any help on where to start looking would be helpful.

[jacwjames]

Not sure on your coach but I have one of these under my dash

I f you do a search on the number you come up with this https://pdxrvwholesale.com/products/scs-servo-control-circuit-board-305-2537-rev-d 

It's a servo controller, and when I look at my wiring diagram from my dash controls It shows up there (I think) as a position control module. 

[Ivan K]

It all depends on what system you have. Since yours uses vacuum, there's got to be a way to switch it to individual actuators.  Mine is a complex matrix of relays and solenoid valves under cover beside the driver.

Where ever the little black tube from your vacuum storage cylinder in the picture goes to, the distribution system and from there to respective actuators to manipulate the air doors. The flaps could even be stuck since the default usually is a defrost mode.

Edited May 18, 2022 by Ivan K

[Georgia Mike]

I guess I’m just going to have to tear into the dash and see what I have. I am going to try and find that thin hose that comes from the ball tank and try and find where it comes to under the dash. Found a thread about that line getting scuffed as it goes thru the fire wall. I guess I will try and get to the back side of the control box and see if I can figure out how it works.

[Frank Bergamo]

My dash vents will get stuck closed occasionally when first turning on AC. Have not figured out what is making it stick closed, but by turning on fan to high setting it will eventually blow the door open, allowing air flow through dash vents. Will be following this to see if someone comes up with a solution!

[Georgia Mike]

Frank, mine does the same thing sometimes when on high for a while it will start just coming through the top vents. Today I started looking at it but couldn’t find the small black vacuum line on the inside. I was looking under the radio and center console area. I can see all of the vent tubes terminate behind the Aqua hot vent it seems. Not sure how to take apart the dash in this area. I didn’t see any vacuum lines connected to the back of dash control box so the vacuum part must be located somewhere else or behind the heater vent. Anyone ever take this area apart? My vacuum pump works and when I put the control to floor air just comes out of the floor. When I change to floor and top vents it comes out of both. When I go to just top vents it stays coming out of the floor and top vents. When I change to defrost I get some air but it still comes out of all the other vents. 

[Ivan K]

Mine is years apart from yours and the vacuum is switched under the gear shifter pad. Looking at your pic, does the circled connector have wires or tubes? Some vehicles have a vacuum switch right in the dash.

[Georgia Mike]

I’ll have to take a closer look at that. I thought it was wires but maybe not. You said yours is under the Allison shift pad?

[Ivan K]

2 minutes ago, Georgia Mike said:

I’ll have to take a closer look at that. I thought it was wires but maybe not. You said yours is under the Allison shift pad?

Yes, I have an access cover beside the driver seat. Pretty bad access to it. Hope yours is different.

[Georgia Mike]

Ivan, you are correct those are the vacuum lines that you circled. I have ordered a vacuum test gauge and going to pull that control box out of the dash. I found some videos on line on how to test this Ford control box so I will update for those with similar problems. For me it makes it easier to learn how something works first before I can fix it so I’m trying to learn as much as I can.