This 1999 Ford E150 van came in with the complaint that the a/c would only blow out of the defroster. The mode actuators in this vehicle are vacuum controlled so checking vacuum is the first point in the diagnostic routine. There is a vacuum hose splice connector under the hood on the passenger side of the vehicle. The hose is red on one side and black on the other. There should be engine vacuum on the red hose. There was vacuum present with the engine running on the red hose. The next test point was under the passenger side of the dash.
The next test point was under the passenger side of the dash. Looking up under the passenger side of the dash there are two vacuum hoses one black and the other white. There is also a junction point for those hoses to connect to the rest of the dash system.
This is what the connector looks like when it is disconnected and pulled down.
There should be engine vacuum on the black hose. Of course the engine needs to be running. There was no vacuum present.
Following the black hose back to the firewall, another connection point can be found. There is a piece of translucent pink hose that joins the interior black hose to an exterior black hose.
Since I knew I had vacuum to the black hose under the hood and I had none at the interior firewall, I surmised that the hose was damaged somewhere in between. I could not see exactly where the hose went from under the hood so I just wanted to run a new hose. I used a 10-12 gauge splicing connector and spliced the black hose to a piece of 12 gauge wire.
The wire was about four feet long and I tied a knot on the other end to prevent pull through.
I carefully wiggled and pulled the hose and wire back through from under the hood. I found that there was a vacuum check valve and a dry rotted piece of rubber hose that would have attached to a vacuum reservoir.
I looked and looked for the vacuum reservoir and could not find it so the next step was to remove the battery and the battery tray.
Still no sign of a vacuum reservoir.
It turns out that the vacuum reservoir is located under the HVAC case assembly. Between the case and the inner fender. The next picture shows what the reservoir looks like. I bought a new one to get an idea of the shape, size and possible location. I did not want to remove the entire case assembly I started looking at options to install it in a new location.
With the battery tray removed I noticed that there was an extra hole that was not used in mounting the battery tray. The vacuum reservoir fit nicely on the side of the bracket and the mounting holes lined up.
After securing the vacuum reservoir I attached a new hose and ran it up to the top of the HVAC case.
I had to drill a hole in the plastic battery tray to clear the head of the new bolt that was installed to mount the reservoir. I used the dirt ring to identify the location of the new hole.
The battery tray installed over the mounting bolt.
I had to reconfigure the hose attachments to the vacuum check valve as follows. The part that I have my finger on in the next picture is the hose that attaches to the vacuum reservoir. The short black plastic hose was relocated to the opposite end of the check valve and the long plastic hose attached to the tee fitting and routes back to the inside of the vehicle. The rubber ends that are on the black plastic hoses are different sizes so I had to use a small pick to free the rubber ends from the black plastic hoses.
Using the same piece of wire that I had left in place, I pulled the long plastic hose back to the inside of the vehicle and reattached the connections. In the process of attaching and removing the guide wire I lost a minimal 1/4 to 1/2 and inch of hose length. That did not matter though as the relocation procedure actually made up for that amount and more.
The part number for the vacuum reservoir is YC2Z-19A566-AA
The vent controls now worked as designed. In case you are not familiar with the whole idea of check valves and vacuum reservoirs they are installed to help prevent vacuum door movement under medium to hard acceleration when engine vacuum drops. Without these parts the vent positions would shift every time the vehicle was accelerated.