2006 F250 Diesel 4X4 blowing A/c only from defroster. Checked vacuum line from pump. Pump has power and 14lbs of vacuum. Does anyone have a vacuum diagram? Any other suggestions?

 

Defrost only is definitely a vacuum leak and if it's 14" that's low. Does it hold that or is that with the pump running?

Some real quick (and free) checks:

- I'm not sure if the '05-'07 models have the MAX A/C vacuum operated valve in the heater line. It's on the passenger's side up under the cowl on my truck. Check to see that the grey vacuum line is securely attached.

- For my truck, Inside the cab under the glove box is the tee connection where this taps into the vacuum line. You have to remove the decorative trim under the glove box to get a good look at it. Check to make sure the connections look solid and that the connector isn't cracked or split.

If it's always defrost it is most likely somewhere between the cab and the ESOF solenoid that will pulse the hubs (mounted to the fender was between the vacuum pump and battery. I've had that thing go bad before.

If it were me I would half-split to figure out where to chase it. Pull the lines off the solenoid and plug them (with a helper's thumbs is the easiest). Turn the key to the ON position and let the pump cycle. When does it turn off? Does it turn off? Is your ventilation still in defrost in all settings? These pumps are meant to be cyclic and do not like to be run continuously, that's what the reservoir is for. If things are working well then it's at least the solenoid. If it's still not working it's the pump, reservoir, or vacuum lines/connections (including the cab).

The hardest part of this is that the truck is 12 years old and rubber dries out. Any connections you disturb can easily be damaged so be careful.

Unfortunately I don't have a vacuum diagram for the '06.

 

There was a vacuum schematic somewhere under the hood when the truck left the factory. Unless it was damaged or removed, it should still be there.

 

Mine does that, but oddly enough only when I throw it in 4 low.

 

That means you have a leak in the vacuum hub-lock system.

 

I figured as much. Just haven't gotten around to looking at it yet.

 

 

Cracked PVH solenoids are a pretty common problem. However, that will not cause the issue to be restricted to only when engaging or disengaging the front hubs as jcook77 described, the issue will be full time.

It's very easy to diagnose a cracked/leaking PVH solenoid. Just cap or pinch off the vacuum supply line that goes to it and see if your HVAC outlet controls work properly then. I would recommend doing that before replacing the part.