How JustAnswer Works:

  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.

Ask Chuck Your Own Question

Chuck
Chuck, ASE Certified Technician
Category: Mercury
Satisfied Customers: 2100
Experience:  33 Years experience,Ford Senior Master,ASE Master,L1 Advanced Engine Performance
Type Your Mercury Question Here...
Chuck is online now
A new question is answered every 9 seconds

2005 Mercury Mountaineer: v6..the ac goes to the defroster vents

Customer Question

2005 Mercury Mountaineer 4.0l v6 AWD. AC is on regular vents, blowing cold as it should, during acceleration, once the car gets to 45 mph the ac goes to the defroster vents, once past 50-55 mph it switches back to the regular vents, if you come back down to below 40 then accelerate again, it will not do this. It seems every time you are at a dead stop then accelerate, this happens. Very WEIRD! I felt the air coming from the defroster, it is air conditioning air. What may be causing this? I have tried taking the ac off of auto and have even turned the defroster on and back to the regular vents. Nothing seems to remedy the issue. I have even sat in park with the accelerator at WOT, it hits the rev limiter at 3.5K but the issue doesn't exist in park.
Submitted: 4 years ago.
Category: Mercury
Expert:  Tim replied 4 years ago.
First check the black vac line that comes in from under the hood and make sure it is fully connected under the dash.Than you will need to check the line from the firewall and trace it to the vac canister and make sure there are no leaks. If the line is good than you will need to vac test the canister to see if it is holding vac under load.The lack of vac is what is causing the vents to go to defrost. Defrost is the default for the system when you loose vac so that the windshield stays clear.
Customer: replied 4 years ago.
Ok jsut got in from troubleshooting, I checked and reseated all lines and connections under the dash. No trouble found. I opened the hood to find the two lines coming from the firewall. One goes to the plastic plenum (Black), then there is a grey line, that runs the passenger side of the engine. The line is taped onto a heater hose, appears to be factory black tape then there is a butt connector line goes in, then there is nothing on the other end. Started the car, there is vacuum, I hooked up my gauge to it and test drove.

The problem is gone if this line is plugged or has a gauge on the end. Amazingly enough, when i unplugged the line, the problem came back and it shifted a lot harder, I think I may have found a big problem! Please advise, i know a plug wasnt standard so where does this line go?

Thanks
Expert:  Tim replied 4 years ago.
From the engine the line should have a check valve than run to a tee that runs to the vac canister and to the inside of the truck.
Customer: replied 4 years ago.
Ok so is the vac canister under the dash or under the hood? What does the check valve look like? I shouldn't have an open line correct?
Expert:  Tim replied 4 years ago.
No there should not be any open lines. The canister should be under the hood and the check valve should be a round valve that only allows vac to pull one way.one way you should be able to blow thru the way you should not.That is the piece that actually stops the loss of vac under accel the canister holds the vac so the vents do not switch to defrost but the valve keeps the system from losing the vac.
Customer: replied 4 years ago.
Where is the vac canister located under the hood? Is it up towards the front of the car?
Expert:  Tim replied 4 years ago.

ItemPart NumberDescription
1W701696Vacuum reservoir screw
219A566Vacuum reservoir
3-Vacuum connector (part of 18C581)

Removal and Installation

  1. Remove the vacuum reservoir screw.
  1. Remove the vacuum reservoir.
  1. Disconnect the vacuum connector.
  1. To install, reverse the removal procedure.
Customer: replied 4 years ago.
Relist: Answer quality.
In previous questions I was used to receiving actual diagrams of the part locations, this is a link that doesn't work. I have had to ask too many questions it seems, there is no doubt he knows what he is talking about but lacks the thoroughness that I am used to with JustAnswer. Sorry.
Expert:  Tim replied 4 years ago.

I am sorry if that did not open I will resend another.

graphic

Customer: replied 4 years ago.
Okay, I checked all of these connections last night inside the car. They are good. I guess my question is where does the grey line go, it is just sitting there with nothing to plug into? It runs a heater hose going toward the front of the car, is there an climate control component that is up towards the front of the car, that needs vac?
Expert:  Tim replied 4 years ago.

The vac line on the heater control valve located in the heater hose runs to the control head in the dash.

Customer: replied 4 years ago.
Ok heater control valve is next to the engine a little further down that heater line?
Expert:  Tim replied 4 years ago.
Ok I will opt out and see if another expert can help you further. Do not reply to this it will only cause the question to be locked back with me.
Expert:  Chuck replied 4 years ago.

HiCustomer

 

Maybe I can help you with your situation.

 

The gray line goes to the heater control valve vacuum switch.

 

graphic

ItemHose ColorFunction
1GrayHeater control valve
2BlackVacuum source

 

 

Here is the vacuum schematic

 

graphic

 

ItemPart NumberDescription
118A318Vacuum control motor - panel door
2-Panel airflow
318A318Vacuum control motor - defrost door
4-Panel door (full vacuum position)
5-Defrost door (full vacuum position)
6-Defrost airflow
7-Side window demister airflow
8-Temperature blend door (full heat position)
919860Evaporator core (part of 19850)
10-Air inlet door (full vacuum position)
11-Outside air inlet
1218A318Vacuum control motor - air inlet door
13-Recirculated air inlet
1419805Blower motor
1518495Heater control valve (full vacuum position)
16-Vacuum source
17-A/C vacuum check valve
1819A566Vacuum reservoir
1919B888Function selector switch
20-Heater control valve vacuum switch
2118476Heater core
22-Floor door (full vacuum position)
23-Floor airflow
2418A318Vacuum control motor - floor door

 

It feeds the heater control valve

 

graphic

ItemPart NumberDescription
18287Inlet and outlet hose clamps (2 required)
218495Heater control valve
39E498Heater control valve vacuum connector

 

 

The heater control valve is actuated by the heater control valve vacuum switch (manual climate control) or the heater control valve vacuum control circuit (Electronic Automatic Temperature Control (EATC)). When the heater control valve is closed (full vacuum), coolant flow through the heater core is shut OFF and A/C cooling efficiency is increased.

 

Here is the lines coming from inside the car

 

graphic

 

 

Then they go to these connectors

 

graphic

 

 

The vacuum reservoir is located under the dash next to the blower motor on this vehicle.So the black supply line comes from intake manifold vacuum to the reservoir then to the control head and the heater control vacuum switch then back out to the heater control valve in the heater core hose.

JustAnswer in the News:

 
 
 
Ask-a-doc Web sites: If you've got a quick question, you can try to get an answer from sites that say they have various specialists on hand to give quick answers... Justanswer.com.
JustAnswer.com...has seen a spike since October in legal questions from readers about layoffs, unemployment and severance.
Web sites like justanswer.com/legal
...leave nothing to chance.
Traffic on JustAnswer rose 14 percent...and had nearly 400,000 page views in 30 days...inquiries related to stress, high blood pressure, drinking and heart pain jumped 33 percent.
Tory Johnson, GMA Workplace Contributor, discusses work-from-home jobs, such as JustAnswer in which verified Experts answer people’s questions.
I will tell you that...the things you have to go through to be an Expert are quite rigorous.
 
 
 

What Customers are Saying:

 
 
 
  • AlvinC answered a question about my Ford truck that only someone with an in-depth knowledge of his subject would have known what was going on. Rich D USA
< Last | Next >
  • AlvinC answered a question about my Ford truck that only someone with an in-depth knowledge of his subject would have known what was going on. Rich D USA
  • Because of your expertise, you armed me with enough ammunition to win the battle with the dealer. They are installing a fuel filter and fuel pump at no charge to me. Molly USA
  • I needed help with my car on Saturday morning....got a response in 5 minutes, and it was the perfect solution. Thanks again to your service. Jason V. Kirkland, WA
  • I do know, after going though this with JustAnswer, that I can somewhat trust my mechanic but I will always contact you prior to going there. BR New Jersey
  • Wonderful service, prompt, efficient, and accurate. Couldn't have asked for more. I cannot thank you enough for your help. Mary C. Freshfield, Liverpool, UK
  • This expert is wonderful. They truly know what they are talking about, and they actually care about you. They really helped put my nerves at ease. Thank you so much!!!! Alex Los Angeles, CA
  • Thank you for all your help. It is nice to know that this service is here for people like myself, who need answers fast and are not sure who to consult. GP Hesperia, CA
 
 
 

Meet The Experts:

 
 
 
  • Ron

    ASE Certified Technician

    Satisfied Customers:

    1601
    ASE Certs and Ford Certs
< Last | Next >
  • http://ww2.justanswer.com/uploads/FO/fordguy4u/2011-12-17_222940_HPIM1257.64x64.JPG Ron's Avatar

    Ron

    ASE Certified Technician

    Satisfied Customers:

    1601
    ASE Certs and Ford Certs
  • http://ww2.justanswer.com/uploads/MU/muddyford/2012-6-13_1204_1.64x64.png Chris (aka- Moose)'s Avatar

    Chris (aka- Moose)

    Mercury Technician

    Satisfied Customers:

    1399
    16 years experience with Mercury
  • http://ww2.justanswer.com/uploads/JM/jmcdo28/2012-2-23_01655_resized.64x64.jpg John Mc's Avatar

    John Mc

    Mercury Technician

    Satisfied Customers:

    403
    19 years Ford Lincoln Mercury experience
  • http://ww2.justanswer.com/uploads/wmarti7/2009-4-18_04332_Avatar.jpg Chuck's Avatar

    Chuck

    ASE Certified Technician

    Satisfied Customers:

    287
    33 Years experience,Ford Senior Master,ASE Master,L1 Advanced Engine Performance
  • http://ww2.justanswer.com/uploads/scottz136/2008-12-09_220350_js640_p1010013.jpg scottz136's Avatar

    scottz136

    Mercury Technician

    Satisfied Customers:

    260
    senior master lincoln mercury tech.
  • http://ww2.justanswer.com/uploads/TI/tim37857/2011-10-28_23053_S6301814.64x64.JPG Tim's Auto Repair's Avatar

    Tim's Auto Repair

    mechanic

    Satisfied Customers:

    257
    Have owned a repair shop for 25 yrs.
  • http://ww2.justanswer.com/uploads/DR/drivefast1971/2012-1-12_172422_0009051tQKh.64x64.jpg Ron Z.'s Avatar

    Ron Z.

    - Mercury Tech -

    Satisfied Customers:

    197
    18+yrs experience. State Inspector and Mercury Diagnostics