I dont know the colors, but there is one hose thru the firewall that pulls vacuum on your dash ****. There should be hoses off the **** that go to 3-4 different vacucm cylinders or pistons. The vacuum cylinders run doors for the vent, defrost, floor, and outside air inlet duct doors. As the guys said, if you loose vacuum, the doors close and air goes to the defrost. I would pull a vacuum on the black hose on the engine side of firewall, and then move the dash **** and see if you loose vacuum at some point. It could be a hose fell off the back of the ****/ controller, or a hose is bad to one of the vacuum cylinders, etc.. I dont see that it has anything to do with the temperature ****, except that it sets close and maybe something is rubbing ??

 

vacuum should work good at idle. AS you speed up the motor, the vacuum can drop off. thats what the storage canister does it help maintain vacuum when you push the throttle.

 

I did pull a vacuum on the hose that goes through the fire wall, it held.
there are no moving parts on the back side of EATC, it is all digital.
I also tested the main line in that plugs into the back of the EATC.
I will test the other 3 hoses and see if they hold a vacuum.
It might be the EATC, I have see rebuilt ones on ebay, so they must go bad. plus they charge a core fee so they can get yours and rebuild it.

 

MAYBE THIS WILL HELP OUT EVERYONE LOOKING FOR INFO

 

thanks for the drawing, will save to help others... what was your final problem?

 

I havent fixed it yet, I need to check the vacuum at each tube in the connector end, thats the last step before I say its the EATC.

 

STEVE(ILL) check your private messages

 

IT IS FINALLY FIXED!!!!!!

I changed the 4 o rings inside the EATC or head unit. $2 for parts.
I followed these instructions!!!!
Repaired my EATC module today. - MercuryMarauder.net Forums

thanks JACook

 

Steve, I read your posts about the blend door. Got some of the panels & ducts loose but having trouble getting the duct out I see 2 units above the floor duct. A white square box about an inch high on the right that has a plug going to it and a black round cylinder type on the left that has 2 vacuum lines running into it. Which one operates the blend door?
Thanks.

 

If I may ask. I have a same type problem. I can't find anywhere that this is addressed. Mine will not go to full defrost. I know it is suppose to be default but it never goes full defrost no matte where I put the selector. fan works fine. Almost all air comes out mid level vents. Very small amount through defroster not enough to clear the windshield. I removed the **** and there isn't any problems there. Just don't know where to look. If I can get any direction I would appreciate it.

 

cardone, i might be late to this party, but a small white square with wires is probalby the motor operator/ gearbox for the temp adjustments. The black cylinder with hoses should be a vacuum cylinder. The air selection point (defrost, vent, floor) iis vacuum operated thru 3-4 cylinders.
--kdwell , the default is to go to defrost. If you have NO vacuum, it will go to defrost. If your not getting defrost, then the duct is plugged, or one of the doors inside is stuck and not letting the system go to the "dead" position ... one possibility is the **** is stuck and always puts vacuum to the vent and never defrost, but that would be kind of hard to do.. when you move the ****, you can change air flow to the floor and dash, and a little to the defrost ?? I assume a cylinder is stuck or door stuck on the duct. Drawings a couple pages back show the cylinders and door operation.

 

I unplugged the connector at two of the vacuum actuators and the line had no vacuum in them. I checked under the hood beside the battery the black air line goes into a 3" long white plastic chamber with two lines coming out the side and inlet on one end and outlet on other end. One of the two small lines is broke and plugged. Don't know where it went. The other goes to a switch valve on the firewall. There is vacuum coming out of the white chamber going into the fender well heading toward the cab. Just figured if no vacuum was getting into the cab it should have defaulted. Do you know what the white chamber broke line is for? It's the line closest toward the fender? I will try to test the other vacuum actuators and see if they work.

 

Is the diagram of the vacuum system the same for a F250 without automatic temp control.?

 

I dont know for sure, but my opinion is the diagram above is very close to what the manual systems are on the F!50 and 250.. No need to be really different.

 

When I applied vacuum on the actuator I heard a crunch inside somewhere. Now I do have defrost. I'm wondering if the door or actuator is actually bad. Is it difficult to get to the door the opens the center vents?