A/C blows only out defrost on c class E450 ford

This fix ^^^ is essentially what I did. The concept is to bypass whatever's bad without having to access it.

UPDATE:

If it were I, I wouldn't want to wait for the test results. I needed to know anyway and got out this afternoon with my Mity-Vac. The new Acme Road Runner Bomb spherical vacuum reserve tank from Dorman is NOT leaking. That's good because I put LocTite on the 1/4" nuts/bolts and all I had was the Red... Also, the controls are not leaking. That's REALLY good and you can tell if you look at the pix on BAT. What I found was that the Dorman Two-Port Check Valve is NOT holding vacuum. Picture at as a "Y" with the stem connecting to the engine vacuum supply. One branch goes to the Reserve Tank, the other to the HVAC Control Valve (knob on dash, looks like a switch but it's a vacuum select valve). Vacuum held on both Branches, so Tank and its hose were not leaking. Neither the new hose I ran to the Control Valve not the HVAC itself leaking.

I'd suggest you do this. Find the connection with the red tube. Disconnect and start engine. Unplug and should be vacuum on it. If so, reconnect it. Then go into passenger side foot well and find the black tube coming out of the HVAC cabinet.
Cut it like I did. If NO vacuum there, do the repair as I explained with another reserve tank and check valve. Both the reserve tank and the check valve are inside the HVAC cabinet. Pull on the black tube and you'll find it has a built-in grommet. Pull gently from there and you'll hear hard plastic hitting the inside of the cabinet at the hole. That's the Check Valve. It's in there WITH the reserve tank and no way to isolate which is leaking and there's no easy way to access them anyhow.
If you cut the black tube at the HVAC cabinet and there IS vacuum there, patch the break with a short piece of vacuum hose and then you're committed to going into the dashboard. Details for that are on BAT but of course I'll help any way I can.


So, either the Dorman Valve is a Restrictor and not a complete shutoff, or the one I bought is a leaker. I'll write Dorman and ask. If you're in a hurry, I'd say get the yellow and black one shown on BAT. Both it and the Dorman tank are available at Amazon. The only commonly available tanks seem to be those round ones from Dorman. I got the one with one hose connection. There's another with two connections. You could go from vacuum source to check valve to one of the connections then from the other to the controls. I chose to use the single with a two-port valve. The black and yellow one would connect the same way as what I now have in place.

Both Vacuum Tank AND Check Valve are inside the HVAC cabinet as mentioned above.

My recent experience is here.

Everything checked out OK after this repair, BUT, there's still a revert-to-defrost-on-hills condition that I haven't had time to go back and check for. My GUESS is that the new Check Valve is defective. Since you're interested I'll try to look at it again soon, but probably not till Tuesday or Wednesday. Really busy the next three days.

Meanwhile, more detail, more pictures, here on BAT. It goes on for three pages, the solution I implemented is on Page Three.

Loss of vacuum.
An internet search will find several work around that are way cheaper than the $900 the dealer will want. Defrost Only is the default mode built in.

The problem is that Ford placed the vacuum tank and check valve inside the A/C
housing. To replace these (which frequently go bad) the A/C has to be discharged and the housing removed. Very labor intensive.

The work around is a $12 vacuum tank with builtin check valve, available from most auto parts stores and a little vacuum line.

Search the web and you will find good direction from several Ford Owner sites.
Make sure you add the vacuum tank and check valve, not just running a new vacuum line. Without the tank and check valve you will lose vacuum on hills and when accelerating and the A/C controls will revert back to the default mode until it has built up vacuum again.

Vacuum line or a bad vacuum valve. Vacuum valve pulls a flapper door to switch between defrost or dash vents. Could also be a jammed flapper. Leave, etc. My Jeep had a broken arm on the flapper. Had to take the dang dash apart to get to it.

Vacuum lines cracked or broken at fittings. Had the same thing happen on my GMC Safari. There were 3 separate vacuum lines. One had a crack in it, and the other one was broken off at the plastic fitting where the rubber line connected. They were hard to reach at the back of the engine.

vacuum line off under the engine compartment