When I bought my 03 E-250, the A/C would only blow through the Defrost Vents (this is the "No Vacuum", Default position of the damper doors controlling airflow under the dash). The shop wanted over $650 to analyze the problem -- NO WAY !! I bought the Ford Shop Manuals from e-bay and determined that between the firewall and the A/C control switch (on the dash) there was only a vacuum check valve and a vacuum reservoir. So all i needed to do was bypass the vacuum reservoir and check valve. First, let me tell you how to determine if bypassing the check valve and vacuum reservoir will fix your problem... Under the hood, on the firewall (passenger side) is a vacuum line that passes through the firewall and provides vacuum for the A/C and heater control dampers, there should be a vacuum connector in the line about where the line passes above the blower motor, disconnect this line and start your engine, place a finger over the line and determine if you have vacuum, this should be a fairly strong vacuum. If the vacuum is weak at this point your problem is the vacuum line between the engine and this point, replace it. Reconnect the vacuum lines. Next, on top of the dashboard is an access panel, under this panel is a cconnector with five or six vacuum lines going to the dashboard A/C switch. Disconnect the vacuum lines and start the engine if the vacuum is working properly the connector (male side), where the Black hose attaches, will have vacuum at this port. Cover the vacuum port with your finger and hold it there, does the vacuum feel strong? Is the vacuum as strong as it was at the firewall connector? If your vacuum is fairly strong the next thing to check is the reservoir and check valve, keep your finger over the vacuum port for about a minute, this will allow the resevoir to store the vacuum, turn off the engine and continue to hold your finger over the port for another minute, remove your finger slightly and feel if there is any vacuum remaining in the resevoir after you remove your finger, if not, then the vacuum resevoir and/or check valve are bad. Here's how I created an easy, and CHEAP, solution to this problem. I used a long section of vacuum line (5 - 6 feet , 2 meters) and a generic check valve to mimic the reservoir, I stuffed the vacuum line behind the dash and spliced my new line into the back side of the A/C control switch, IT WORKS GREAT! Here are the details... First, remove the dash front panel and the radio to gain access to the back side of the A/C control switch. The dash panel removal required removing the headlight **** (use small screwdriver to depress the locking tab) and bezel, then two screws above the instrument cluster, the remainder of the panel is held in place with push pins that will release when gently coaxed Note: remove the Cigar Lighter wire(s) by pressing on the release tab on the electrical connector. Once the panel is off you can release the radio by pressing in on the mounting brackets on both sides. With the panel off you can remove the A/C control switch. I ran a new vacuum line from the firewall connector toward the back of the engine and drilled a hole in the side of the Passenger footwell. The hole was placed slightly above and forward of the cowell strap bracket. I used a gromet in the hole and Hi-Temp Siicone to seal the hole after i threaded it through. I routed the new line up behind the radio bracket and installed the check valve here. I then coiled about five feet vacuum line (one size larger) and secured the coil with zip ties. I placed the coil (this creates the reservoir) in a void between the radio and instrument cluster. The other end of the coil was routed to the back side of the A/C control switch after reducing the hose size. I cut the BLACK vacuum hose going into the A/C switch and used silicone to secure it so it would not wiggle free (note: be sure to cut the black hose long enough to make it easy to attach your new vacuum line, ALSO, be certain the silicone does not plug up the end of the black hose). Test your fix and reinstall the radio and dash panel. Let us know how this worked for you. Good Luck and Keep on Truckin !!