99 ford f250 truck 5.4 need vacuum line schematics

The vacuum supply line to the climate control unit could be broken if it is gas engine. If ti is a diesel engine the vacuum motor or pump ,depending on the set up, is not working properly.

Sounds like a broken vacuum line..When have no vacuum it defaults to defrost...Check outside by the firewall on the passenger side..There should be a black and gray vacuum lines..Trace each one down and look for one of them broken or unplugged..They are notorious for that...

Defrost is the default when the controller is not receiving vacuum from the intake manifold. Look for the small vacuum line going from the engine intake manifold to the firewall and trace it to the control switch. If the vacuum line looks OK, try to pull the vacuum connection from the control switch. Then start the car and see if there is vacuum coming to the connector from the line that you traced from the engine. If no vacuum, the line has a leak--retrace to the manifold. If there is vacuum, your switch is probably leaking. You can buy a new vacuum switch from Ford or some parts stores. More questions, please let me know.

I would check under the dash to see if a hose has come disconnected for the middle vents

Look over on thw passenger side under the hood, close to where you recharge the a/c, going into the fire wall, will be a vacuum line with a one way valve tie into the vacuum line, disconnect it and blow through it, should only be able to blow through it one way, if it does it both ways bad valve, replace it.That's what holds the vacuum for the vents.

The air control doors on your vehicle are vacuum operated and shift by themselves to a "default" position [which is defrost] if the vacuum is lost. I would suspect that you have a broken or leaky vacuum supply line near the engine somewhere which is preventing vacuum from ever reaching the control panel. Look for a broken or leaking small 1/8" or so diameter black plastic vacuum line near the rear of the intake manifold area on the engine. This line may go to a plastic vacuum reservoir or it might just go right to the firewall and pass through it with a group of other items [it varies from model to model] If you can't find it you might need to have someone at a service facility track it down for you. Should be a fairly simple fix. Good luck, hope this helps a bit!

look under the hood and dash for broken vacuum lines as that is what as that is what actuates the air flow doors

The gray vacuum hose is for your heater control valve. It shuts it off when on max a/c . Repair the hose and put it back on. It can also cause your a/c to blow out the defrost.

defrost is fail safe mode. cehck for a broken vacuum line from the engine to the heater control head. check vacuum reservoir under hood for leaks.

do you have a source of vacuum? normal problem occurs on the vaccum line from the engine to the vacuum switch of the car. unplug the vacuum hoses from the rear of the switch and feel if there is hose that is sucking your finger. if there is none, then trace the line towards the engine firewall out to the engine compartment. it could be broken that is why it is stuck in defrost mode.

i hope i was able to help.
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