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AC Foot Face troubleshooting by MikeC


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#1 importwarrior

importwarrior

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Posted 27 October 2014 - 04:54 AM

Information provided by:
MikeC

There are three vacuum actuators in the interior heater-A/C circuit:
* One conrols the fresh air/recirculate function - it moves the door on the air box underneath/behind the glove box.
* One directs air to the windshield defroster vents.  It's the vertically mounted one in Importwarrior's pics.
* And the 3rd one controls the face-foot selection.  This is the one pictured in this thread with busted rubber bellows.  It is mounted horizontally with the pushrod facing towards the front of the car... it's mounted behind the black plastic ductwork as Importwarrior noted.  Not impossible to remove/replace but not easy either.

The fresh/recirculate and foot/defrost actuators are "typical" actuators with one vacuum hose feeding them.  Apply vacuum and they move, release vacuum and internal springs move them back.  The face/foot one is different though: it has 2 vacuum nipples, one on each side of the diaphragm.  Apply vac to either one and you get face or foot, apply vacuum to both and you get the face+foot blend.  If the rubber bellows leaks, the vacuum that selects face mode just bleeds out so you end up with a face+foot blend... mostly foot though.  This actuator has not been available from Mitsu for many years now.  However... you can replace it with a one-port actuator like the foot-defrost one if you are willing to give up the face+foot blend function.  You just cap off  one of the vac hoses that used to go to the dual-port actuator.

2-part epoxy slathered across a split/tear in the rubber bellows will fix it for a while... until another crease in the rubber bellows splits.  Another option is to find a way to re-skin the rubber bellows: imagine taking a rubber tube (like cutting up a balloon) and clamping it to:
* the metal pushrod
* and the body of the actuator near the other end of the rubber bellows.
Basically, just make a new bellows.  As long as the rubber piece is flexible you can make a fairly long-term repair.  Larger vacuum hose is way too stiff to work.  I used some heat-shrink tubing on a busted junkyard actuator as an experiment, basically making a new skin on the rubber bellows.  It worked a bit... but ended up a bit too stiff.  Heat shrink tubing that was left sloppy loose in the middle of the bellows - only shrunk to a tight fit at the ends - might be better.

As for how the vacuum system is set up:
The #4 port on the throttle body as noted in the pics on this thread is unported intake manifold vacuum.  it sees vacuum or boost pressure.  There is supposed to be a vac hose on the #4 port, that hose runs up and along the air conditioner hose (factory setup had it zip-tied to that hose) behind the engine into one of those dinky white things.  Those dinky white things are check valves - basically one-way pipes.  They allow air to flow from one side to the other but block air flowing FROM the #4 port - i.e. they block boost pressure from getting past them.  The other side of this white check valve goes through a T or two and ends up at the vacuum reservoir caniser - that black tank between the ABS claptrap and turbo heat shields.  The other side of the "T" eventually hooks to a vacuum hose that dives downwards along the firewall to a small copper pipe stick through the same hole in the firewall as the air conditioner refrigerant pipes.  Inside the car - under the dash - that copper pipe goes over the top of the evaporator box (passenger footwell - the evaporator is the air conditioner part that actually cools the air) to a series of electric vacuum switching solenoids.  Thesesolenoids are used by the a/c computer to direct the flow of vacuum to the three actuators I described at the top of this post.  If you remove the ash tray and shine a flashlight into the opening you'll see the solenoids.  Replacing those solenoids takes a fair bit of dash disassembly... fortunately those vac hoses don't suffer engine bay temperatures so they generally don't fail.

The vast majority of problematic dash vent stuff are:
1: busted bellows on the face-foot actuator.

2: vac hose leaks or disconnected hose on the #4 manifold port.  A too-large diameter vac hose will have a loose fit on this port and will tend to blow off the port during turbo boost operation.  A small hose clamp - like the spring rings used on the turbo wastegate hoses - helps a ton.

3: busted white check valves or missing check valves.  The under-dash actuators will not survive exposure to turbo boost pressure.  Those vavles must be present and must be working.  They should allow airflow TOWARDS the engine intake manifold (the little arrow on them points towards the vac hose going to #4 port).

4: problems with the a/c control computer.

5: downstream of the white check valve and T's are more vac hoses (and another check valve and T or two) for the cruise control stuff.  Leaks in that stuff will reduce the available vacuum to the under-dash actuators.  The vacuum pump (mounted between the headlights) powers the cruise control stuff only - a white check valve isolates it from the dash actuator system (hence the need for the vacuum reservoir to power the dash vent actuators during on-boost conditions).  And the vacuum pump only runs when the cruise control is turned ON and boost pressure is present... most of the time that pump is OFF.

I can't recall anybody having bad solenoids.  The foot-defrost vacuum actuator and fresh/recirculate actuator are far more reliable than the face-foot actuator too.

To get to the face-foot actuator, the basic steps are:
1: remove lower dash ("knee panel") panel on driver's side.

2: remove carpet panel on center console in driver's footwell.

3: I remove the long skinny air duct that runs along the bottom metal dashboard strut above the driver's shins for more work room.

4: Pull off that black elbow visible in Importwarrior's pics.  it just snaps onto the center heater assembly.  it branches into two ducts going upwards and snaps into two different plastic pipes.

5: Now you can SEE the face-foot actuator.  Still darn difficult to reach though.  Look above the bottom metal dashboard strut and you'll see a huge/thick wad of wiring... push that wiring out of the way and you'll get an opening big enough for your hand.  When I finally get the actuator out, it pull it out through this opening; easier than trying to pull it downwards.

6: Look at the pushrod coming from it.  It has two itty-bitty screws attaching it to linkage on the heater box.  Undo those two screws.  They'll probably be super tight and you can't push on the screwdriver much as the linkage just blends.  If you eyeball the linkage, you'll see a single metal screw with a large plastic washer that seems like it'd be easy to remove and leave the itty-bitty screws alone.  DON'T FALL FOR THIS!  There are several spring-loaded pieces held by that one screw and it's virtually impossible to re-assemble stuff unless you get the entire heater assembly out.

7: There are two of those soft/easily stripped gold metal screws Mitsu loves so much holding the actuator to the metal bracket.  The screw heads face the firewall so they're hard to see... an offset screwdriver or stubby screwdriver helps.  Or you can try to eyeball the 3 screws that attach the metal bracket to the heater core box.

8. Undo the two vacuum hoses and position them such that they won't spring back into inaccessible spots under the dash.

9. Pull the actuator out.

You'll twist and bend a lot doing these steps.  Lots of fun working underneath the dash.


mike c.

B-71 87 TSI ~ RIP

Black 87 Starion ~ Mess SOLD!!!

Proud New 89 slightly Rusted Fiji Owner !!!








#2 importwarrior

importwarrior

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Posted 27 October 2014 - 04:56 AM



please read this from the FAQ

http://www.starquest...howtopic=131748

this is the one i am talking about showing the Bad rubber accordion sleve on it.
if it leaks the foot face will not work.
this one in pic is bad you can see the black rubber piece that broke off still on the plunger near the tip of his  (KEV ) index finger.

Posted Image

it is mounted above the black plastic pipe in the right of the pic you posted.

Posted Image

B-71 87 TSI ~ RIP

Black 87 Starion ~ Mess SOLD!!!

Proud New 89 slightly Rusted Fiji Owner !!!







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