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Old 10-21-2010, 06:31 PM   #1
olopezm
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Solution to A/C switching vents on its own under engine load.

Hello people, I've seen many of you (me included) with the same symptom:
The A/C system switches from vent to defrost mode under engine load (going uphill or overtaking another car).

It is caused by a vacuum leak and as far as I've seen most of us had the same problem a loose red hose, here are some pictures of where to start looking first.


This is the hose that gets disconnected from the back passenger side of the intake manifold.


This is where that hose should be connected to.


This is the other end of the same hose, it has a check valve on it and this side is connected to the vacuum reservoir and into the firewall to the dashboard to control the A/C system.


This image is just to show the location of the vacuum reservoir, you'll have to remove the cowl in order to see it properly, if you don't you can still reach the reservoir but it will be a bit hard since you don't have much space.


Here's the vacuum reservoir and the hoses from another perspective.

Hope this information helps in the future, I don't know if it would be a good idea for the administrators to stick this thread on the first page, what do you guys think?. Any questions please let me know!.

Best regards,

Oscar.
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Last edited by olopezm; 12-14-2010 at 12:19 AM.
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Old 10-22-2010, 04:39 PM   #2
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Re: Solution to A/C switching vents on its own under engine load.

Done!
I needed to figure out how to do the sticky thing anyhow.
This is an excellent write up.....thank you very much.

As a side note, where the air goes inside the van, Defrost, Vent or Floor is driven by vaccum from the intake manifold.
With NO vaccum to the deflectors, all the air will go to the defrost position.

Vaccum comes from the back side of the upper intake manifold through a thin vaccum line, which has a check valve in it.
The vaccum line goes 2 places, Into the passenger compartment and to a small "box" resevoir.
The Resevoir holds the vaccum in the control system to maintain the climate control airflow in the selected position when the motor is under a heavy load, when there is very little vaccum in the upper intake manifold.
It also holds vaccum in the system for when the motor is not running.
The check valve keeps the vaccum from being lost into the intake manifold under low vaccum conditions.

The vaccum inside the intake of the motor is at maximum when the motor is at idle with no load, and at minimum under maximum accelleration or heavy load.

This is NOT the same system that controls the temperature of the air......but controls where the air blows.

Air temperature is controlled by a blend door that controls how much of the air will pass over the always HOT heater coil.
This door is driven by a electric motor......a common failure being stripped teeth on the nylon gear(s) or a broken part.
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Links to my pictures, intended as an aid, not a replacement for, a good repair manual.
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http://www.flickr.com/photos/4157486...781661/detail/
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Old 10-22-2010, 05:42 PM   #3
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Re: Solution to A/C switching vents on its own under engine load.

No problem wiswind!, I did this in order to somehow thank to the automotive forums and all the people for all the help I have received.

Hopefully this will help many other people.

Best regards,

Oscar.
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Old 06-10-2011, 07:14 AM   #4
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Re: Solution to A/C switching vents on its own under engine load.

Hello all ,
This is an excellent effort bay all. I changed check wall but not the vacuum reservoir. Although I checked the reservoir and all the pipes they had no leak. The problem had some improvement but it is still there. After driving 60 to 90 miles the problems recurs. The cold air is directed to defrost when engine accelerates, outside tempreature is high or there is upslope. Reservoir and manifold are separated by check valve why then vacuum leaks?
Best regards
AzharJ
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Old 06-10-2011, 08:06 PM   #5
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Re: Solution to A/C switching vents on its own under engine load.

Hi Azharj,

Im pretty sure you either got a defective check valve or has been installed the wrong way.

As you said, if everything was tested and is fine there should be no more problems and taking into account the fact that you have air coming out from the front vents, meaning there are no leaks under the dashboard, the only thing left is the check valve AGAIN.

Regards,

Oscar.
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Old 06-11-2011, 04:40 PM   #6
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Re: Solution to A/C switching vents on its own under engine load.

Dear Olopezm,
Thanks I will try again and let everyone know the results.
With regards
AzharJ
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Old 06-17-2011, 02:11 PM   #7
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Re: Solution to A/C switching vents on its own under engine load.

I can't believe it took me 10 years to find this forum. I have been looking for the location of that pesky hose for a year now. I used to be an ASE mechanic, I've been out of automotive for 12 years now. I'm on the industrial side working for one of, if not the largest forklift companies in the world. I don't think most people are even aware of this issue. This is a great post!!! I'm gonna love it here!!
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Old 06-20-2011, 01:52 PM   #8
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Re: Solution to A/C switching vents on its own under engine load.

Hi all members,
This is a food for thought: why ford company made this stupid system of moterising the controle with vacuum and plastic geard motor? why not good quality plastic gears and electric wired controles instead vacuum lined or only simpler wires to pull and push to open Or close the doors? and the the simple parts very expensive.
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Old 06-21-2011, 04:47 PM   #9
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Re: Solution to A/C switching vents on its own under engine load.

Quote:
Originally Posted by azharj View Post
Hi all members,
This is a food for thought: why ford company made this stupid system of moterising the controle with vacuum and plastic geard motor? why not good quality plastic gears and electric wired controles instead vacuum lined or only simpler wires to pull and push to open Or close the doors? and the the simple parts very expensive.
AzharJ
Actually is not just Ford who have this system, other brands have the same vacuum system too, my pontiac does. The reason is because in the event you have any vacuum related problems during extreme weather you might be freezing inside the car but, at least, you can still drive with a good visibility with the defrost option. Even with electric actuators there are still problems, you can search for Blend Door Actuator (which is part of the HVAC system in cars and controls air temperature) and see it is a common problem too.

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Old 08-08-2011, 11:46 PM   #10
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Smile Re: Solution to A/C switching vents on its own under engine load.

I had vehicle serviced and discovered that the hose inside the dash has a leak. Has anyone removed the radio/ash tray-cup holder and serviced the hose inside the dash without removing the dash itself. Seems like if the hose was visible inside the dash it may be reachable to slip a slice onto that part of the interior hose. any thoughts guys.
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Old 08-12-2011, 09:53 PM   #11
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Re: Solution to A/C switching vents on its own under engine load.

Quote:
Originally Posted by jerryw2314 View Post
I had vehicle serviced and discovered that the hose inside the dash has a leak. Has anyone removed the radio/ash tray-cup holder and serviced the hose inside the dash without removing the dash itself. Seems like if the hose was visible inside the dash it may be reachable to slip a slice onto that part of the interior hose. any thoughts guys.
Not sure about the process but I do know some users removed those items in order to get to the vacuum lines. I think that's the answer you were expecting.

Good luck!

Oscar.
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Old 08-20-2011, 01:22 AM   #12
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Re: Solution to A/C switching vents on its own under engine load.

jerryw2314
It is very easy to remove. There are a lot of mails and photoes to illustrate it Just type "changing AC Blender motor windstar" or "HVAC system windstar" on net search and u will find answer.
I made this instrument by turning to stiff wires into U which fits in the wholes in the front of the heater. Push the wires in the wholes and while pulling the radio apart them
http://www.instructables.com/id/Rewi...Ford-Windstar/
http://www.youtube.com/watch?v=iSbzR...eature=related
http://www.youtube.com/watch?v=2tN2nZjjw_M
http://www.heatertreater.net/Windstar%20Listing.html
http://www.lifeasbob.com/CategoryVie...BWindstar.aspx

I fixed the issue of vent deflection to the defrost position. I made two amendments:
1.) fixed check valve vertically see diagram No. 1.
2.) repositioned the whole check valve and vacuum reservoir assembly inside, under the dashboard
I fixed the valve vertically because the air can travel from the white side to the black side only. In the central cylindrical part which is between the two white and one black tubes (marked red), (diagragm No. 2&3) there is small thin circular plastic disk like membrane. This plastic membrane closes the way back to white tubes. If the valve is vertical, the sheet will be horizontal, thus closing the white tubes by its weight, all the time.
One of the white tubes of the valve is connected to the vacuum canister. From the other white tube , a black hose goes to the control knob, from which different hoses go to the different actuators. See the connection diagram (NO. 4) of the hoses. Leak can occur at any of the connection points between manifold and the red hose, hoses and check valve, vacuum canister, control knob, and actuators; and the hoses, check valve, vacuum canister and actuators themselves. However, the most probable site of leak is on the engine side, where the changes in the temperature due to engine heat and cold external temperature can damage the plastic parts by making them inflexible.
I removed the hose, the canister and check valve, which I had replaced recently, plugged the open ends, dipped all of them in a bucket of water and applied air pressure to the other end. I came to know that all the joints and vacuum canister were leaky, even though I had secured all the joints with silicon and steel wires. There was a small phalange of residual plastic material along the whole length of the tubes of the valve. This phalange was preventing airtight fitting of hoses with the check valve. I repaired the leak of the vacuum canister with glue and filed the phlange to smoothen the tubes of the check valve. I took a long new hose. Connected it to the manifold on the one end and firmly tied the other end to the black hose, which is connecting the vacuum canister to the control knob, and pulled the new hose inside.
I could find much place behind on the glove box just on the passenger side of the central console and fixed the check valve and vacuum canister on the new place; so that access any future service will be easy. Other advantage was that it gave much space to replace the metallic Y shaped heater hose later on.
Alternatively, leak can be detected by creating 15-inch vacuum in all hoses, check valve, canister, control knob and actuators; fall in vacuum by 1 inch per min will indicate leak in thesystem but not the site of leak. Blowing under water method is simple not requiring any pump/ tool simply blowing in the vacume can detect leak and also the site of leak not possible to detect the leaky actuators knobs etc. See link http://www.automotiveforums.com/vbul....php?t=1074091
http://www.automotiveforums.com/vbul....php?t=1050429
http://www.automotiveforums.com/vbul...02#post6921202
Attached Images
File Type: jpg Fig 1 check valve vertile.jpg (66.1 KB, 65 views)
File Type: jpg Fig 2 vacuum check valve1.jpg (35.2 KB, 61 views)
File Type: jpg Fig 3 vacuum check valve.jpg (34.6 KB, 55 views)
File Type: jpg Fig 4.JPG (85.5 KB, 62 views)

Last edited by azharj; 04-01-2013 at 04:12 PM.
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Old 10-22-2012, 03:40 PM   #13
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Re: Solution to A/C switching vents on its own under engine load.

I am having the similar problem and will check my vacuum hoses. However, I also have a problem where the rear climate control system only blows hot air via the floor or roof vents, regardless of the settings. Is this another fault than the vacuum system? Thank you.
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Old 10-24-2012, 07:03 PM   #14
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Re: Solution to A/C switching vents on its own under engine load.

Hi Corney, welcome to the forum!

The front HVAC is controlled via vacuum. The rear system is all electrical so your problem lies somewhere else; the Rear Electronics Module controls all of it's functions.

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Old 03-03-2013, 03:52 PM   #15
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Re: Solution to A/C switching vents on its own under engine load.

Thanks for posting this thread as important. I was having this same trouble where the vent would switch to the defroster when the engine was under load for a few years now. It turns out my problem was self-inflicted.

When I took the plenum off a few years ago, I forgot to hook the vacuum line back up to the vacuum reservoir and couldn't control the vent switching at all. Not knowing the real connection point was on top of the reservoir (I couldn't see it with the cowling on), I saw what looked like an appropriate size fitting to connect it to. Turns out that was just a plastic post that fit my vacuum line fitting. I connected the vacuum line to that and I could control the vents under most conditions.

After reading your post and seeing the pictures you attached, I realized what I did was wrong and decided to check this again. With the cowling removed, it was very obvious where this line plugged in and my problem is solved! Thanks again!
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