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Author Topic: 2004 mercury grand marquis - air conditioner switches from vent to floor to defs  (Read 2788 times)

Offline boogettyman

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can someone tell me why this happens & what there is for an easy fix.  .  .  .   ? you can turn the air on and it s cold as ever -but, it will not stay on the vent mode. . .  hit a bump and it switches on its own to floor -def. -to the different modes.   need advice on what might be the problem causing it. . . thanks.  ??? ??? ??? ??? ??? ???
« Last Edit: May 25, 2012, 03:03:54 PM by boogettyman »

Offline kev2

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classic description/sympton of a vacuum leak in the HVAC -

  Any chance you have a CK engine light on?
  DO you have access to vacuum diagrams ?

Offline boogettyman

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NO CHECK ENGINE LIGHT .  .  .  CAR RUNS PERFECT .  .  .  ? I DON'T HAVE ANY DIAGRAMS FOR VAC SYSTEM. .
« Last Edit: May 25, 2012, 04:54:50 PM by boogettyman »

Offline kev2

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try to avoid all capitals - it translates as yelling in forums.

sounds Like a actuator vac line, tell us is this automatic or manual control panel HVAC?
It is a holiday weekend cant get a diagram - maybe someone has and can still post a dia for help.

 other than checking vac lines underhood from eng to vac reservoir recheck any recent work that may have disturbed vac lines,  dash etc...or you could try listening for the tell tale sound -unlikely but something to try - till we get a diagram.

PS - any chance you have a 'mityvac' type vac tool?

Offline The old man

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This vacuum diagram is for the manual ac.. The electronic is the same except for #19 is EATC controlled instead of manual.

Offline Jim Fairbanks

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Here is the one for the electronic....Jim
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Offline boogettyman

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Sorry about the cap's. .  No I Don't have a mityvac. . .  thank's for info . .

Offline boogettyman

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Thank You for the Diagram , I will try to figure it out . . . . .

Offline boogettyman

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Thank-You also For the Diagrams --Hope to figure it out. . . . Somebody Did Do some work under there , they had to replace motor in the adjustable brake pedal , maybe they knocked something loose.  don't quite understand the automatic / manual question ????

Offline NickD

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Defrost is the default position for low or no vacuum, most typical problem is in the check valve either leaking in the reverse position, or its hose to the intake manifold has a tiny crack in it as that manifold does get hot.  Just cut off about a half an inch off of it and plug it back on.

It feeds the reservoir that  effectively stores the vacuum, need that, when you open your throttle, intake manifold vacuum drops to nothing, so this maintains the vacuum for the MVAC system.  Sometimes they have a small crack in the case, a piece of plastic, can be repaired with hot glue.

The is the vacuum source, a really nasty problem is have an intake valve that is not fully closing killing the intake manifold vacuum, easy to check with a vacuum gauge hooked up to that nipple the check valve connects to, should read around 20"/Hg at idle if at sea level.  This drops an inch for about each thousand feet you are above sea level.

A more trouble some  problem is the grease in the vacuum mode switch dries up causing a leak, haven't found one yet I couldn't take apart, clean, and use new silicone grease.  Normally cost a small fortune to replace as they want to sell you an entire control panel.  But some Fords have a separate mode switch, have to look that up.

Never had a defective actuator yet, but another possibility if the diaphragm is leaking.   Vacuum circuit is extremely weak, so even the slightest leak can cure it.  On some vehicles with an automatic parking brake release, that actuator can be the problem.

Would not waste my money on a Miti-Vac, cheap plastic, one drop of gas gets in, melts and seizes up, would only buy a metal one with replaceable O-Rings.  Has a vacuum gauge installed and works like a vacuum gauge.  Can just connect that to your intake manifold start the engine don't pump it and read your intake manifold vacuum.   Can also connect it to your reservoir and pump it up to 20, after you reach that, should hold indefinitely.

Can also connect that to the hose that feeds the system, and pump it up to 20, that should hold as well.  A necessary tool.

Offline kev2

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. . . . Somebody Did Do some work under there , they had to replace motor in the adjustable brake pedal , maybe they knocked something loose.  don't quite understand the automatic / manual question ????

That is where to start up at the top of brake pedal arm, the area worked on is close to the defrost actuator,I would look for a loose hose -kinked cut etc. Above diagram item #19 hose 2,3

For the manual vs automatic controls-
 manual is the common controls knobs levers to set desired temp- blue cooler red hotter. old school
 Automatic is a digital reading you would set the temp as a desired number-  ie 72 degrees would appear in LED display... new (expensive) school
« Last Edit: May 26, 2012, 02:46:46 PM by kev2 »

Offline boogettyman

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L E D read out . . . . . . . . . . .  automatic,,,, digital readout.

 

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