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A/C blowing from defrost

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Old 07-09-2018, 08:39 PM
Obx4X4
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A/C blowing from defrost

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?
 
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Old 07-10-2018, 09:24 AM
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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.
 
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Old 07-10-2018, 01:37 PM
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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.
 
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Old 07-10-2018, 01:42 PM
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Mine does that, but oddly enough only when I throw it in 4 low.
 
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Old 07-10-2018, 02:06 PM
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Originally Posted by jcook77 View Post
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.
 
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Old 07-10-2018, 02:15 PM
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I figured as much. Just haven't gotten around to looking at it yet.
 
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Old 07-12-2018, 08:22 AM
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Originally Posted by jcook77 View Post
I figured as much. Just haven't gotten around to looking at it yet.
I have had my truck only blow out of the defrost vents for over a year and every mechanic I have talked to have told me to replace the vacuum pump or the blend door system. (Which I did replace both) and nothing happened, I recently came across a video that a guy had the same problem and he first tried replacing the vacuum lines behind the front drivers side tire and it only worked for a little while then he found out about the “hub locking actuator” and replaced it and it worked. I just bought one yesterday and will be putting it in today hopefully it works. So maybe try that piece, I got it from oriellys for like $60. Hope that helps!
 
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Old 07-12-2018, 08:26 AM
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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.
 
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