Question about 2001 Cadillac Sts

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Air only from defrost.

Where do I find the vacuum that causes air to come from defrost only problem?

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  • knowabit May 22, 2009

    So do I have to take the dash off? Any hoses under the hood?

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There are only 2 things that cause this, most common is a loss of vacuum from the engine to the ac/heater control heat in the dash, the other is the control head is defective.

Posted on May 22, 2009

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The hoses are attached to the back of the selector and then run up behind dash.

Posted on May 22, 2009

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Need pitcure of vaccum lines on 1999 Ford Ranger v6 3.o air and heat blows only threw the defroster.


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Item Part Number Description 1 18A318 Vacuum Control Motor-, Panel/Defrost Door 2 18A478 Panel/Defrost Door (Full Vacuum Position) 3 - Defrost Air Flow 4 - Side Window Demister Air Flow 5 18B545 Temperature Blend Door (Full Heat Position) 6 19860 A/C Evaporator Core 7 19A813 Air Inlet Duct Door (Full Vacuum Position) 8 - Outside Air Inlet 9 18A318 Vacuum Control Motor-, Air Inlet Duct Door 10 - Recirculated Air Inlet 11 18527 Blower Motor 12 19A566 A/C Vacuum Reservoir Tank and Bracket 13 - Vacuum from the Engine Intake Manifold 14 19B888 A/C-Heater Function Selector Switch 15 - Vacuum to the 4x4 Hub Solenoids 16 18495 Water Diverter Valve (Full Vacuum Position) 17 18476 Heater Core 18 18A559 Floor/Panel Door (Full Vacuum Position) 19 - Floor Air Flow 20 18A318 Vacuum Control Motor-, Floor/Panel Door 21 - Panel Vent Air Flow

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Air Flow Control
Air flow control is accomplished in the following manner:
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vacuum control motor-i4bq0ig33y1522pr2d2rrkk3-2-0.gif

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1 Answer

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It sounds like you may have a vacuum leak. If you have a vacuum leak it will cause the air to only come out of the defrost vent no matter what you have the controls set to. Hope this helps you out and gives you some place to start looking.

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Climate Control - Heat and cool work fine. Air flow is directed to defrost /floor. No indication (Sound or sight) that the vacuum diaphrams are being activated. The display on the dash matches the...


Does your vehicle have manual or automatic climate control ? You system is stuck in floor an defrost mode ?

03 mercury grand marquis hvac air flow .-13qahwfdndst2y1hypmr2cdq-4-0.gif Item Part Number Description 1 18A318 Vacuum control motor-floor/defrost door 2 - Defrost air flow 3 18A478 Floor/defrost door 4 18476 Heater core 5 19860 Evaporator core 6 19805 Blower motor 7 - Outside air inlet 8 19A813 Air inlet door 9 18A318 Vacuum control motor-air inlet door 10 - Recirculated air inlet 11 18B545 Temperature blend door 12 18A559 Panel door 13 - Panel air flow 14 18A318 Vacuum control motor-panel door 15 - Floor air flow 16 - Vacuum from the engine intake manifold 17 19A563 A/C vacuum check valve 18 19A566 Vacuum reservoir tank and bracket 19 19980 EATC control
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vacuum lines hvac 03 grand marquis-13qahwfdndst2y1hypmr2cdq-4-2.gif Item Part Number Description 1 White Air inlet door 2 Yellow Floor/defrost door 3 Red Floor door 4 Blue Panel door 5 Black Source vacuum 6 - Not used


VACUUM APPLICATIONS CHART-ELECTRONIC AUTOMATIC TEMPERATURE CONTROL Switch Port Vacuum Harness Hose Color Func- tion Manual Override Selector Buttons OFF MAX A/C NORM A/C VENT FLOOR FLOOR/ DEF DEF 1 White Air inlet 2 Yellow Floor/ panel (partial) 3 Red Full floor 4 Blue Panel 5 Black
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