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#4132598 - 01/11/22 05:16 AM HVAC Air Flow Issue
White Falcon LS Offline

Posting Addict

Registered: 01/01/02
Posts: 19130
Loc: SoCal
If I turn on the HVAC to any position where it's suppose to vent from the dashboard towards the cabin (VENT, NORM A/C or MAX A/C - manual controls), it vents in defrost mode to the windshield instead. After some time goes by, and the engine is at idle with high vacuum (e.g. at a stop sign), it'll switch to the dashboard air vents on its own.

If this was a constant vacuum leak, I reckon it would continually be stuck in defrost mode, but this one has me scratching my head. Pretty sure it's a vacuum issue, considering my auto parking brake release also stopped working. Thanks!
Lucifer: '01 Grand Marquis GS Convenience
Tuned By Marty @ Mo's Speed Shop

In Memory of Ned Nuss, Rick Richardson and Matt (2vmodular)

#4132616 - 01/11/22 09:59 AM Re: HVAC Air Flow Issue [Re: White Falcon LS]
Old_Guy_Stu Offline

Over the Hill

Registered: 04/28/19
Posts: 2790
Loc: Cleveland, OH
Definitely a vacuum issue. Maybe the vacuum accumulator or the line going to it? There's only 2 miles of vacuum lines in these cars, so have at it!

1988 CVLX Formal Roof (Love Boat) POTM July 2019, Aug 2020, & Oct 2021, 58K
E-code lights w/ relays, LEDs w/ switchbacks, 15x8 Ansen slots w/ 255/60 BFG's, Kenwood stereo, various hacks.
This, of course, was merely the semi-delirious notion of a fever-patient, but I remember that it struck me at the time as being eminently practical and feasible.

#4132666 - 01/11/22 03:52 PM Re: HVAC Air Flow Issue [Re: White Falcon LS]
Davidzq Offline

Registered: 01/19/15
Posts: 661
Loc: Seattle, WA
Do you have manual or electronic controls?
The EATC unit uses o-rings which eventually crack and leak. I would suspect the one for the panel door has cracked. #007 is the size of the o-rings.

It's also possible the panel door hinge has broken, leaving the door stuck.
David Hensley
Member of Northwest Panthers Car Club

2008 P71, Norsea Blue SAP
-Message Center cluster retrofit
-Towncar Signature L heated power seats
-Long overhead console
-Compustar remote start/security

#4132790 - 01/12/22 08:49 PM Re: HVAC Air Flow Issue [Re: White Falcon LS]
Dmblanch Offline

Registered: 11/13/19
Posts: 631
Loc: Utah
Given the frequency of o-ring failure, that'd be my first bet, fortunately its cheap and easy to replace them all. Everybody who buys them has extras left over.

1) 2002 White P71 - 89K miles. 2) 2003 B&W P71 - 74K. 3) & 6) & 11) 2005 White P71 - 54K, 74k, 115K. 4) 2011 Black P7B - 79K. 5) 2008 White P71 - 95k. 7) 2004 Silver P71 - 104K. 8) 2004 DT Red LX Sport - 111K. 9) & 10) 2010 White P7B SAP - 104K & 106K. 12) 2006 White P71 - scrapped. 13) 2007 Gray LX Sport - 125k. 14) 2006 White MGM LS Premium - 93k.


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