E450 AC Vent Vacuum Issue -- standard fix failed -- other suggestions?

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E450 AC Vent Vacuum Issue -- standard fix failed -- other suggestions?

July 03, 2021, 07:15:24 pm

Hi folks,

Our 2000 Mid-Bath has what I've come to understand is a rather common failure, actually on all E-series Ford vehicles.

Our vacuum-controlled vent actuators are no longer working, and the system has defaulted to using the defrost vents. This is the standard failure mode, as I understand it.

After researching on youtube, I found a number of users that have solved this problem by by-passing the buried beneath the dash vacuum check valve and reservoir, and relocating those underneath the passenger knee plate. I bought Ford parts and made that fix, and as far as I can tell, everything was done correctly, but in my case, it did not correct the problem.

I've checked the actuator that controls the AC front vents, and it can move (manually), but is not responding to the vacuum system.

Anyone else experience this problem, when the "simple" fix did not work? Any ideas of what component is the likely culprit? I'd really prefer to avoid the $1000 labor bill for some Ford mechanic to removing the dash on my 20 year old chassis, as I can only imagine the new failures that might introduce. Would love to keep trying a repair myself, as time and parts availability allows.

We're getting AC as we drive, but it is slow to cool, and won't cool well unless we're driving at a decent speed.

I welcome sage advice from the Board of LD Repairs!!

Thanks in advance,

Re: E450 AC Vent Vacuum Issue -- standard fix failed -- other suggestions?

Reply #1 – July 03, 2021, 07:56:34 pm

I’m interested in any responses as well. My TK shuts down flow when I go up hills and the the revs pick up. I had a Chevy van that did the same thing. I assumed that vacuum can not keep up under certain driving conditions.

Re: E450 AC Vent Vacuum Issue -- standard fix failed -- other suggestions?

Reply #2 – July 04, 2021, 07:52:38 am

Not helpful, but the under the dash fix with Motorcraft parts worked for me. Check that the hoses are connected properly.

Re: E450 AC Vent Vacuum Issue -- standard fix failed -- other suggestions?

Reply #3 – July 04, 2021, 08:29:14 am

Never heard of using Ford Parts. Only one part and some tubing is needed. Details here.
The Lazy Daze Companion: Cab AC - Air Flow Cuts Off Under Acceleration

Re: E450 AC Vent Vacuum Issue -- standard fix failed -- other suggestions?

Reply #4 – July 04, 2021, 10:22:56 am

Thanks Don! Now I need to check into a similar fix for my Taurus 😁

Re: E450 AC Vent Vacuum Issue -- standard fix failed -- other suggestions?

Reply #5 – July 04, 2021, 03:02:32 pm

A few months ago I implemented fix based on the link Don provided above. However, I found it easier to run the engine vacuum line around the passenger fender well and then inside under the passenger side of van. (Rather going through firewall). Worked great and saved $1000.

Re: E450 AC Vent Vacuum Issue -- standard fix failed -- other suggestions?

Reply #6 – July 08, 2021, 01:20:35 am

Thanks everyone for your replies. So it seems nobody has any "suspects" on what could be continuing to cause my default defrost setting for my vent system.

Per Steven Jill's suggestion, I will double check my repair connections, but am pretty sure I did them all correctly.

If anyone else has dealt with this issue, and found other parts that were the culprit, I'm interested to hear your inputs. Thanks all!

Re: E450 AC Vent Vacuum Issue -- standard fix failed -- other suggestions?

Reply #7 – July 08, 2021, 04:09:25 am

Hi Steve; Routinely there is a leak in the vacuum hose system under the dash that operates the vacuum pistons that operate the dampers that switch air to different places. The default is 'defrost' as a required safety measure. So you can see out of the window. In my experience rodents most usually take a chunk out of a hose. It could be a bad vacuum 'motor'. That is what they call the piston flap actuators. If you have a hand vacuum pump, you could try activating the main damper to see if it is moving when vacuum is applied.
If your hand pump has a gauge, I'd intercept a vacuum line coming from the engine bay and see if you can pump a vacuum, and if it stays steady for a time. If not, there is a leak. RonB

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