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Author Topic: Life in the Service Lane . . .  (Read 44862 times)
Oldcarsarecool
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« Reply #150 on: September 27, 2015, 09:35:33 AM »

Customer States:  A/C inop .  .  .
June 25, 2015
Part 1 of 2





I see this type of concern all the time.  A/C failures do occur with a degree of regularity, which is not surprising considering a majority of the vehicles in our fleet are more than 15 years old.  The Georgia summer heat doesn't help matters much.  When something happens, the customer will bring the vehicle in for service and say something like, "The a/c quit working," the exact definition of which varies.  Verifying the concern, (ALWAYS the first step in the repair process), will often lead to one of two possibilities.  

In a majority of cases, the HVAC system operates properly, but just doesn't blow cold air.  Leaks in the system can develop over the years and miles.  As refrigerant escapes, the system becomes progressively less effective until it reaches the point where it doesn't cool at all.  Diagnosis focuses on pinpointing the source of the leak and repairing/replacing components as necessary.

Today's concern, however, followed a slightly different path.  The 2010 Ford Explorer in my bay blew ice cold air, but not through the dash vents.  Moving the control knob would allow air distribution to switch between the floor and windshield vents.  This is a case of the system, itself, not operating properly despite being fully charged.  I did some investigating and discovered the source of my dilemma.


The component in the photo below is called a Plenum Chamber.





In layman's terms, a Plenum Chamber is basically an air handler for the HVAC system.  Air enters the Plenum Chamber seen above from the bottom of the chamber which is connected to the heater case.  A series of vacuum operated actuator motors, (which can also be seen in the photo above), open and close doors within the unit according to what setting is requested, (i.e. a/c comes out the vents, defrost comes out at the windshield, heat comes out the floor, etc.).  This particular system is a "Dual Zone" unit which allows for driver and passenger to select individual temperature settings, hence the two doors.  Air exiting from the chamber in the photo above would be directed to the dash vents.  Air exiting from the chamber in the photo below would be directed to the defrost vents.





Ice cold air not coming from the dash vents indicates a problem with the Plenum Chamber or one of its components.  And where is the Plenum Chamber located ?  It's in here !





The Plenum Chamber is attached to the heater case behind the instrument panel.  Removing the radio and HVAC controls from the center of the dash allows you to see it.





But that doesn't necessarily mean you can get to it.  The instrument panel has to come out of the way first.





Thankfully, I don't actually have to actually remove the instrument panel from the car.  I just need to move it rearward away from the heater case.  The passenger's side is pretty straight forward.  A few wiring harness connectors need to be unplugged.  Several fasteners that help hold the instrument panel to the body of the car need to be removed.





The driver's side is a little more involved.  The modern instrument panel design routes all the wiring contained therein to a few large connectors.  This is much more convenient than having to disconnect each individual component.  Most of the larger wiring harness connectors are on the left side.





The steering column shaft also needs to be disconnected.  With the wiring harness connectors unplugged and the steering column disconnected, removing the fasteners allows the panel to be slid rearward .  .  .


« Last Edit: September 27, 2015, 08:48:56 PM by Oldcarsarecool » Logged

Oldcarsarecool
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« Reply #151 on: September 27, 2015, 09:36:12 AM »

continued .  .  .
Part 2 of 2





Below is the outlet from the heater case where heated or cooled air from the blower motor gets distributed.  When heat is requested, air is directed out at the floor vents, one of which can be seen in the photo below.  When a/c or defrost is requested, air is directed out through the large rectangular opening and into the Plenum Chamber, (the chamber's bottom foam gasket can be seen on the right in the photo below).





Notice that the Plenum Chamber stays attached to the instrument panel.  The fasteners that hold the chamber in place are accessed from the front of the panel via the opening behind the radio.





The vacuum lines for the actuator motors on the chamber must be disconnected as well.





Removing the Plenum Chamber is a not-as-simple-as-it-seems process of twisting and turning.








And voilĂ  !





Installing the new Plenum Chamber involves following the previous steps in reverse order, a time consuming, but not necessarily difficult task.  The question now becomes why did I have to do all of this ?





The photo below shows the connection from the vacuum motor (R) to the vent door of the new Plenum Chamber.  





When a/c is requested, this vacuum motor opens the door which directs air through the dash vents.  This is done via the vacuum motor drawing the silver metal rod inward, thus moving the door on a pivot point.  So what happened ?





The small plastic tab that connects the vacuum motor to the door broke off.  When this happens, the door is free to move at will, in this case, to the "defrost" position.  Any air coming from the heater case gets directed to the windshield regardless of where the selector knob is set.  

So the root cause behind this entire labor-intensive process can be traced to a small tab made out of cheap plastic.  I've encountered this before in our older Ford E-Series vans which feature this same type of design for the rear HVAC unit.  The primary difference is that all of the vans I have seen with this problem are 15 - 20+ years old.  This Explorer is from 2010.  I hope I'm not seeing the start of another trend .  .  .
« Last Edit: September 27, 2015, 10:22:41 AM by Oldcarsarecool » Logged

racer91
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« Reply #152 on: October 06, 2015, 09:01:48 PM »

This post reminds me of my Heater blend door actuator on my P71.

Luckily i was able to ghetto rig it and will fix it when i have to. It was stuck in the A/C position. Its now toasty.


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Oldcarsarecool
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« Reply #153 on: October 12, 2015, 11:51:33 AM »

Zip ties can be a tech's best friend ! 
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Oldcarsarecool
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« Reply #154 on: January 18, 2016, 12:38:50 AM »

I give someone credit for creativity .  .  .
August 20, 2015





A 2004 Ford Econoline van arrived for routine maintenance this evening.  I opened the hood to begin the service and made an interesting discovery.








This is one of the more interesting repairs I've seen come through the shop over the years.  I had to stare at it for a minute or so, allowing the information to be taken in and processed, not that I understood things any better afterward.





Somewhere along the line, the brake master cylinder reservoir cap went AWOL.  Someone made this discovery and tried to implement a fix.





Rather than coming to the Automotive Center and having us fix the issue, (which is why the center exists in the first place), said person or persons got creative.





This cap/tin foil/zip tie repair would be fine for getting the van to the Automotive Center so the proper repair could be made.  I give someone credit for trying.  The only question I have is how long has it been this way, which will never be known.





I keep an extensive assortment of spare parts for just this kind of issue and installed the proper reservoir cap .  .  .
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RatherBNarizona
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« Reply #155 on: January 21, 2016, 07:17:38 AM »

the Plenum Chamber repair looks like a pain in the ass. If you gave me the tools, that would probably take me days to figure out. Like, a whole lot of days.
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Mac
Oldcarsarecool
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« Reply #156 on: January 23, 2016, 05:16:23 PM »

It's appearance is more intimidating than anything else.  The modern Ford instrument panel is actually pretty well designed.  All the electrical components are routed to the sides so the connectors that need to be disconnected are all together.  The overall design theme becomes apparent once you work on a few .  .  .
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