Unique A/c Problem

[michaelh4]

I got a '01 V6 automatic. The AC works fine, blows cold, but when i'm driving and i press the accelerator about 50% or more, all the air stops blowing out of the vents. This only happens going down the road; i tried to replicate it sitting in park but it blows continuously, so only in drive.
If i left off the pedal, cold air immediately begins blowing again and there is no temp change in the air; always cold. Also, I can't hear any clicking turning the blower fan on/off.
It's just not making sense that at a certain point on the accelerator, the fan stops blowing.

 

[wmburns]

Engine vacuum is used to control the vent damper motors. There is a check value and a vacuum reservoir that keeps the system working at times when the engine vacuum is low.

In your case, either there is a vacuum leak after the check valve or the check value isn't working. When the engine vacuum drops, there's not enough vacuum to "hold" the dampers in the vent position. The damper spring then switches to the default position which is the defrost setting.

 

[michaelh4]

so where exactly is the check valve on my car; I've looked on the passenger side of the engine bay up near the firewall, but I can't seem to see it, am I just missing the obvious here?

 

[wmburns]

It's in the passenger compartment. This could also be leaks in the vacuum lines.

Do you have a Ford service manual? If interested in getting a copy for yourself I may be able to help. PM if interested.

 

[michaelh4]

ok I need a little more detail, the haynes manual i have doesn't say anything about the passenger compartment and i've checked all the vacuum lines under the hood, where am I specifically looking?

 

[wmburns]

There is very small vacuum line that passes through the firewall on the right hand side.

The Ford service manuals have more details.

 

[michaelh4]

Ok so i took a flashlight and looked at the firewall. Is it the A/C line that goes into the firewall that you're talking about or am I just missing it? And could it be a vaccuum line on the A/C(there's a rubber hose line along the valve cover on the passengers side)? I haven't located the vaccuum reservoir either.

 

[wmburns]

Post a picture of the right side of the firewall from the engine bay side. Hint, a vacuum line is not the same as the hard AC line.

 

[Ufg062003]

Control head is controlled by vacuum also there will be red blue yellow and so on lines goin to it so test it ,default mode is defrost when there is a vacuum leak most of the time it's a broke line under the hood or the control head