First U have 2 make sure U have Vaccume @ the belt driven Vac.Pump,then U have 2 repair the Vac.Leak. Some Dodge truck have Vac.lines near the battery & Bat.Acid will make the Vac. line Brake.Some of the Vac.Hoses are in a plastic loom that keeps the hoses & wires 2gether.Loss Of Vac.2 the control is the problem.
I have a 2001 - my problem solution was the vacuum hose that is located right under the weatherstriping for the hood. Just about the center of the block, there is a rubber elbow that faces down and bends to the rear of the truck. The is a small vacuum line that is in a plastic wire loom that should be connected to this elbow. My hose fell out of the elbow and was against the firewall. I re-connected this hose and put a small zip-tie on it(to avoid the problem in the furture) and it now works perfectly! P.S. The 4 wheel drive will not engage the front tires with this hose off either. I found this out the hard way as I got my truck stuck on a slimmy boat ramp trying to pull out my boat!
you have a vacuum leak. defrost is the default when a vacuum leak is present.
Because a diesel engine does not create vacuum and the vacuum pump is necessary to operate things like the vacuum assist brakes and cruise control.
Vacuum pump the same vacuum pump that works automatic locking hubs on the 4wd
You have a leak in the vacuum supply to the ac control.
More than likely the vacuum feed line from the engine has been disconnected or cracked. When there is no vacuum supplied to the HVAC it reverts back to the defualt position, the defroster.
Check behind the heat control panel to be sure that the vacuum hoses are all securely plugged into the control switch. As a safety measure on all cars, if you lose vacuum altogether, the default position for air direction is on defrost, so you can always see out of the windshield. Jake McCahn
Check for a vacuum leak either under the hood or under the dashCheck the vacuum actuators under the dashCheck the selector control Defrost is the default for this system
try your local junkyard
Diesel engines do not have enough vacuum themselves
You have a vacuum leak in the fan control system somewhere... not easy to locate the leak
Selector control Vacuum under hood and under dash Vacuum actuated motors under dash
You have a vacuum line disconnected probably under the hood. The HVAC controls are operated by vacuum and when there is no vacuum it system goes into defrost mode.
It's a vacuum leak somewhere in the system. There are several vacuum lines that operate the blend doors on the system. If there is a leak where the system will not hold vacuum, it will default to defrost automatically.
most likely there is a vacuum leak. check the vacuum lines leading from the intake the the interior heat and a/c control. look for cracks around the vacuum lines. check the vacuum canister and check valve.
There is most likely a vacuum leak on the line from the engine to the air conditioner control.
If you have the electronic climate control system it most likely is a Vacuum Hose leak Start under the hood on Passenger side and replace all hoses from canister to under the dash this should help. With a Vacuum leak it defaults to defrost mode
Something about the vacuum linr being unattached, maybe from the firewall. im trying to figure out the same. The main vacuum supply line is disconnected or cracked, probably near the engine. All the HVAC doors operate on vacuum. When there is no vacuum the HVAC system goes into defrost mode.
The first answer is correct and heres where the leak most likely is. Under the hood, against the back firewall close to the middle, you'll see a vacuum tree. Several hoses plug in here. Both the Tempo and Topaz I've had this happen to, occured here. Look for a unplugged hose or a cracked or dry-rotted hose and replace as needed. Defrost is the AC/heat system's default position. Likely you have lost vacuum to the control head. When there is no vacuum to control the functions then it will default to the defrost vents.
This A/c system uses a vacuum system to control it's mode(vent , panel, defrost, floor) and defaults to defrost due to a vacuum leak in the system. The first area to check is the vacuum check valve, found at or near the vacuum source. Then check the vacuum hoses to the vacuum reserve canister. If no problem found in these areas, then further diagnoses of the control head and HAVC assemble, by a qualified a/c technician.
It sounds like you have two separate problems. Incorrect routing of ventilation is usually caused by bad vacuum motors or loose vacuum lines, but remember that A/C is -supposed to be- routed to the defrost vents when controls are in the Defrost position. The dim temp control readout could be due to a number of causes, but probably isn't related to the other issue you describe.
7.3 Diesel has a vacuum pump.... belt driven
The e-150 heat/ac system uses vacuum to control the air direction through a series of doors. There is most likely a vacuum leak causing the defrost door to keep air flowing away from the dash vents.
It is for vacuum storage. It keeps blower mode from switching to defrost when accelerating. The mode selection is vac controlled and will default to defrost when vac is lost or low. This stored vacuum keeps that from happening
I'm not completely sure,but i think vacuum hoses control that
Because you have a vacuum leak in the system or your vacuum canister is leaking. When you accelerate the vacuum from the engine will drop. That will cause your system to loose vacuum and the floor/defrost door will go to its neutral position. To keep the vacuum up you have a canister that will hold vacuum. It must be air tight.