I own a 04 f-450 that has a/c coming out of the defroster. I removed the "dog house" and found rodent droppings. The red vacuum line from the manifold to the connector where it changes to black looks good. i understand that the canister and check valve are located in the right fender well so wanted to bypass them with a new canister and check valve. If I do this will I bypass something that is also connected to this vacuum source in the fender well? I found a small black vacuum line by the passenger kick panel that has been chewed in two. Where does it connect to? The other white vacuum line that goes to the vacuum motor is ok. How do I remove the passenger side kick panel? I pressurized the black vacuum line by the battery to 4PSI and can't detect where the leak is. Any recommendations?

you dont have any vacume at the ball resivore under the hood.. some are located on the hood its self and some under inner fender.. look for a black plastic ball lookin thing with 2 vac lines running to it.. one should be all rubber and one should be plastic with rubber ends.. the all rubber one is the in line follow it back to the engine and see if it is damaged somewhere, if so repair or replace.. one other place i have found problems is under the dash by the dog house or just above the dog house in the center.. improper installation of the house will kink or pinch the vac line and you will not get any vac at the control head

Vacuum supply starts on the drivers side of the engine. There is a vacuum line going into the brake vacuum assist from the manifold. branching off of that line is a double line that snakes under the intake manifold, behind the valve cover, along side the valve cover on the passenger side headed to the front of the engine. Then it curves to the right side of the engine. One set of hoses from this line goes to a valve control (red and green i think). The other line goes to the vacuum storage ball, it should be black. The vacuum circuit continues out of the ball in another black line that snakes into the firewall. It goes under the heater core black box and disappears under it. Now go into the passenger compartment and drop the glovebox. look to the back right you will see a black and a white vacuum line coming out of the firewall. The black line is your vacuum supply from the engine. It goes up to a little rubber manifold. disconnect the lines coming from the dash switch and check for vacuum on the manifold where the black line is going in. The white line controls the cabin air intake under the glovebox and the thermostat shutoff under the hood. It should only have vacuum when the switch is in a certian position, AC probly. The other three lines coming off the rubber manifold snake behind the dash vent door assemble and come out near the gas peddle. The red one controls the dash vent. apply vacuum to the red hose and see if the vents go to the center dash position/AC. The yellow and blue? ones control the floor vent control near the gas peddle. yellow gives you half floor and half defrost. blue gives you all floor. you can use a small vacuum line to connect the black vacuum supply to each individual line on the manifold and check the function of each vacuum control assembly individually. I hope this helps. On my truck each control unit works fine when i apply vacuum to them individually but when I hook the dash switch up to the rubber manifold it goes to defrost. I tried changing the dash switch and the lines running from the switch to the rubber manifold and the vacuum ball under the hood, nothing works. I suspect I may have leak i just haven't found yet. next step is to get a vacuum gage and start checking the amount of vacuum i am getting at each vacuum line. I'm sure it is supposed to be getting a specific amount of vacuum and will not work if the vacuum drops below a certian level due to a leak in a line somewhere? God bless.

If there is no vacuum to the mode door control motor theheater/A/C system will default to "Defrost" If there is no air coming out the vents or floor - check to see if you have air blowing out the defrost vents. If there is air coming out the defrost, then the most likely cause of your problem is a broken or disconnected vacuum line that feeds the mode control switch. On your vehicle, the vacuum supply line connects to the brake booster hose under the hood. there is a check-valve on the line between the firewall and the brake booster that can fail and leak vacuum. if there is no problem with the vacuum supply line under the hood, then the most likely cause is a bad mode control switch. (switch leaking vacuum)

If there is no air coming out the defrost vents, but you can hear the blower motor running, there is most likely a resriction of airflow etween the blower motor and the air outlet plenum. I have seen A/C evaporators completely cloggedup that will not pass any air. I have also seen paers and napkins that have gotten sucked out of the glovebox area and into the "Recirc" air inlet. Another thing I have seen several times is nests made by mice or other small rodents in the blower motor housing.

They are controlled by vacuum ... a line must have been disconnected or broken when the trans was replaced. Remove the dog house and look for a small vacuum line broken or pulled apart.

what position is the control switch in? does this occur when accelerating?

the door that directs air flow is controled by a vacuum motor. the default position for the door directs air flow to the defrost vents in the event of vacuum loss to ensure the windsheild will be clear of mist. if there is a small leak, vacuum will temporarily be removed when accellerating and the motor will revert to the default position. there are vacuum lines from the control knob to the motor you must check these lines for leaks. the diaphram in the motor may be bad. also check the main vacuum supply line to the control knob. usually red in color. if there is a vacuum storage cannister. it may be leaking. this cannister will maintain vacuum for the circuit when accellerating. engine vacuum decreases when accellerating.

I had same problem . There is a vacuum resovoir tank located behind the left front splash shield . The vacuum line behind the battery goes to it . I removed two 5/32 screws just in front of the tire that hold the splash shield to the fender , carefully flex the shield away from the fender and take a look . I found the vacuum line had come loose , plugged it back on and everything works . Hope this helps

The controls on your Astro are operated by vacuum from the engine.
Because vacuum drops as the throttle is opened to maintain vacuum to those controls a vacuum reservoir is used.
You have a leaking vacuum line causing your problem.
Look for a black line about 1/8th inch diameter coming out of the cab on the left side into the engine bay. You will have to look under the cowl over the engine and you will likely find a rotten piece of plastic vacuum line. Cut the old plastic well back as it will break again soon from heat.Get a piece of rubber vacuum line from your local auto supply that will slide snugly over the plastic. This is where your problem will be at a 95% probability.
If you have any further questions please place them in "add comments" and I will respond to help.
Thank you for using FixYa!

KL

Check to see if is blowing out defrost vents if it is you have a vacuum leek. The tube is hard to get to take of dog house you will see a group of tubes on connected to a clear plastic junction. Once you get the dog house off one of the tubes goes to your manifold vacuum fallow them its very thin and the engine heat makes it brittle and they fall apart . Mine did same 2 shops 500 dollars and they never found or fixed it used window washer tubing to fix 2 years ago still works great,

check vacc line from engine into fire wall. behind batt is where they normally crack and leak. possible from a leaking batt at one time. check black supply vacc line right behind battery