Ok guys, here's my problem. A/C blows from dash vents correctly at idle. During acceleration, it switches to the defrost vents. From everything I've read it points to a bad mode door vacuum check valve. I'm scratching my head though trying to find the check valve. The internet tells me it's on the line from the intake manifold near the vacuum reservoir, but I haven't found it. I also searched the web for a replacement check valve just to see what it looks like, and I can't even find a picture or listing for a replacement. HELP!

 

Okay, further reading some Ranger Forum posts, it appears that the check valve on a 2003 4.0 is probably inside the vacuum reservoir. That's why I can't find it.

Question though: Could the grey line that connects to the heater hose bypass valve be my problem of vacuum loss during acceleration?

 

Okay, I traced the vacuum line from the firewall to the vacuum canister, and canister to the intake manifold. I didn't see or feel any breaks in the lines. Now I strongly suspect it's the check valve that I believe is located in the vacuum canister. Is this something that normally goes bad?

 

ALa-BAst Update:

I disconnected the line from the intake manifold at the vacuum reservoir. Placed my finger over the end of the line and felt plenty of vacuum at idle. Reconnected the line and then disconnected the other line that goes to the firewall at the vacuum reservoir. Placed my finger over the canister nipple that the line connected to and felt little to no vacuum. That tells me my problem has something to do with the reservoir. Maybe it's cracked, or maybe the internal check valve is stuck closed.

Z-My last question for you pros: Do I have to replace the vacuum reservoir with the OEM Ford part (#F67Z-19A566-BA) from the dealer, or can I use an aftermarket/universal replacement reservoir that has two nipples, like a Dorman #47076 from AutoZone? They both look identical even though the Dorman reservoir says it's not compatible with my 2003 Ford Ranger 4.0 4x4?

 

Okay, I replaced the vacuum reservoir and that didn't fix the problem. I ran the dash switch through the different door modes.

These work fine: defrost, defrost/floor, floor, dash, A/C.

This one doesn't work: Max A/C ... it comes out of the defrost instead of the dash.

I dropped the glove compartment door down and I see a vacuum motor (7L5Z-18A318-B). It appears to operate a "door" on the interior of the firewall. My guess is it's part of the Max Air recirculation system. The door is in the "closed" position. When I run the engine and turn the dash switch to Max Air (or any other position for that matter), nothing happens. The door remains closed.

Could this motor/actuator be the problem?

Help!