Please help! AC has a mind of its own. - Ford Powerstroke Diesel Forum
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Old 07-14-2010, 10:41 AM
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Please help! AC has a mind of its own.

Hey guys, I'm new to this forum.

Okay, here's the truck, have an 06 f-250 superduty 6.0, has the fancy push button climate control, fx4, lariat the works.

The problem is, the vents(on the front of the dash, passenger/driver) don't work, and instead, the air is routed up through the defrost vents under the windshield. At first, they wouldn't come back on when the truck was started(when It was previously set), I'd have to turn off the AC, then turn it back on to work. Another condition is when the weather is over 102 it seems to work fine. Now it seems to work when it wants to. Any ideas on what it could be?

Also, Is the vent control vacuum actuated or is it electronic?

I've got a trip across the desert to AZ and AC would be nice.
Thanks in advance to all who reply
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Old 07-14-2010, 10:53 AM
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The system is runoff a vacuum pump. either you have a vacuum leak or the pump is not working. when you turn the key on can you hear the vacuum pump buzzing in the passenger side engine compartment.
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Old 07-14-2010, 11:04 AM
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Quote:
Originally Posted by mudrunninpig View Post
The system is runoff a vacuum pump. either you have a vacuum leak or the pump is not working. when you turn the key on can you hear the vacuum pump buzzing in the passenger side engine compartment.
Thanks for the reply. Yes the vacuum pump is buzzing with the key on. But why would the vents selectively work? The 4x4 always engages the hubs, and those are vacuum actuated. ???


Nice truck BTW
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Old 07-14-2010, 12:27 PM
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If you don't have a vacuum leak, your A/C brain is on crack.
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Old 07-17-2010, 05:31 AM
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i am having the same problem only comes out defrost
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Old 07-17-2010, 08:12 AM
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I'm kind of having the same problem. But I have a vacuum gage installed, so I see what is happening. With AC on and not in 4WD, gage shows 12 - 14 in. Hg and the vacuum pump is off. As soon as I turn on the 4WD, the gage slowly drops to 0 and the AC switches to defrost. The electric vacuum pump is running the whole time. I hear the transfer case engage and the auto hubs seem to engage (I had the truck on jack stands and was hand spinning the wheels). After 30 - 60 seconds, the vacuum all of a sudden starts to build and over the next minute the vacuum builds back to 14 in. Hg and the pumps shuts off. The vacuum holds then and the pump stays off. Also, at about 5 in. on the gage the defrost switches back to AC.

My question is: Has anyone experienced this and could it be the pump is just wearing out? I've checked for leaks with the vacuum at 14 in. and the pump off but haven't found any yet. I hate to buy a new pump if you think it is something else.

Any help would be appreciated!
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Old 07-17-2010, 08:21 AM
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AC out of the defrost only = vac. leak. It is designed that way. It is the signal that you have a vac leak. May not be easy to find, but that is what you need to look for. Good luck.
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Old 07-17-2010, 08:27 AM
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I currently have the same problem. The funny thing is that my 4-wheel drive light comes on, but my front end doesn't actually lock in. I asked abrannan about it and he mentioned its probably a certain electrical component he pointed out to me under the hood. I can't remember the name of it, just that its related to the 4-wheel drive vacuum system and will reroute your ac to the defrost vents. I'll give an update if I find anything else out.
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Old 07-17-2010, 10:10 AM
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Quote:
Originally Posted by zgerm01 View Post
I currently have the same problem. The funny thing is that my 4-wheel drive light comes on, but my front end doesn't actually lock in. I asked abrannan about it and he mentioned its probably a certain electrical component he pointed out to me under the hood. I can't remember the name of it, just that its related to the 4-wheel drive vacuum system and will reroute your ac to the defrost vents. I'll give an update if I find anything else out.

The 4wheel drive light comes on when the transfercase switches into 4wd, that is electronic so it is separate from the vacuum hub system.

When you switch to 4wd, there is also an electronic solenoid close to the vacuum pump that sends a vacuum signal to the hubs to engage them. But if you have a vacuum leak somewhere, the hubs themselves will not be activated even though the transfercase is and the 4wd light is on.

Last edited by GregsSD; 07-17-2010 at 10:13 AM.
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Old 07-17-2010, 11:13 AM
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Quote:
Originally Posted by GregsSD View Post
The 4wheel drive light comes on when the transfercase switches into 4wd, that is electronic so it is separate from the vacuum hub system.

When you switch to 4wd, there is also an electronic solenoid close to the vacuum pump that sends a vacuum signal to the hubs to engage them. But if you have a vacuum leak somewhere, the hubs themselves will not be activated even though the transfercase is and the 4wd light is on.
Do you know what that solenoid is called so I can buy one somewhere and try it out?
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