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acstechgm

acstechgm 4/1/2010

2002 Dodge Ram 2500 Base 8 Cyl 5.9L

Body & Interior

Fan Switches Vents Randomly

Air randomly switches back and forth from dash vents to defrost vents.

1 Answer


HouseCallAuto

HouseCallAuto 4/1/2010

Here is some real good data. You can see for yourself what the cause is>>

Driving with the A/C on under light or heavy acceleration, the airflow will stop blowing out of the vent ducts and switch to blowing out of the defrost vents.
Tests/Procedures: 1. Check the vacuum check valve at the right side of the intake manifold and check the second check valve in the line to the left of the receiver drier.

2. If they are good, check for a leaking line or defective and leaking vacuum motor in the Heater Ventilation Air Conditioning (HVAC) system.
Potential Causes: Plastic Line
Vacuum Check Valve
Defective Vacuum Motor

Tech Tips: When vacuum is lost to the system as in acceleration, the HVAC system will switch to the defrost position as a safety default.
Diagnostic Codes: None
Author: Brainard Janicki
Average Reported Mileage: 124159



Confirmed Fix Summary

Confirmed Fix 15 - Vacuum Check Valve
2 - HVAC Vacuum Hose
1 - Check Valve
1 - Vacuum Hose



Confirmed Fix Details

Tech Reported Fix Details Confirmed Fix
Brad Edwards
May 02, 2007 2000 Dodge Ram 1500 Pickup, 5.9L, Vin Z, Eng Cfg V8 *
Vacuum Check Valve
- I was having trouble finding out why the HVAC was shifting, after trying several different aftermarket vacumn check valves I finally got one from Dodge and that fixed the problem. I dont know why but the aftermarket valves would not hold vacumn while driving. Vacuum Check Valve
David Lee
November 26, 2007 2002 Dodge Ram 1500 Pickup, 4.7L, Vin N, Eng Cfg V8 *
Vacuum Check Valve
- Replaced vacuum check valve at firewall, very common on these models, did nor fix problem. After consulting IDENTIFIX checked for and found another check valve at manifold which had failed. This check valve is not present on most models. Good info. Vacuum Check Valve
Stephen Webb
May 22, 2009 1999 Dodge Ram 1500 Van, 5.9L, Vin Z, Eng Cfg V8 *
Replaced Vacuum Check Valve
- changed vacuum ck valves. like brad edwards I found that oe vacuum checks work better than aftermarket. Vacuum Check Valve
Jay Fortino
February 21, 2008 1999 Dodge Ram 2500 Pickup, 5.9L, GAS, Vin Z, Eng Cfg V8, USA/Canada *
Vacuum Check Valve
- installed vac check valve near fuel rail on pass. side of engine. not holding vac. Vacuum Check Valve
SCHMIDTSHAW1
March 05, 2009 2000 Dodge Ram 2500 Pickup, 5.9L, GAS, Vin Z, Eng Cfg V8 *
Replaced Vacuum Check Valve
- found grease in the inlet vavle/line blew out and all is working OK. Vacuum Check Valve
Terry D. Wren
April 30, 2008 1996 Dodge Ram 1500, 5.9L, GAS, Vin Z, Eng Cfg V8 *
Vacuum Check Valve
- FOUND VACCUM CHECK VALVE BAD AT INTAKE MANIFOLD/CRACKED/LEAKING Vacuum Check Valve
Larry Throndson
October 21, 2009 1996 Dodge Ram 1500, 5.9L, GAS, Vin Z, Eng Cfg V8 *
Replaced Vacuum Check Valve
- replaced both check valves in right vaccum hoses Vacuum Check Valve
Denny Mandeville
September 19, 2007 1998 Dodge Ram 1500, 5.2L, Vin Y, Eng Cfg V8 *
Vacuum Check Valve
- Replaced second check valve by receiver Vacuum Check Valve
Bob Parra
September 06, 2007 1999 Dodge Ram 1500 Pickup, 5.9L, Vin Z, Eng Cfg V8, USA/Canada *
Vacuum Check Valve
- INSTALLED UPDATED VAC CHECK VALVE Vacuum Check Valve
Tommy Gregory
July 06, 2009 1999 Dodge Durango, 5.9L, Vin Z, Eng Cfg V8 *
Replaced Vacuum Check Valve
- bad check valve Vacuum Check Valve
Bill Taylor
June 09, 2006 2000 Dodge Ram 1500 Pickup, 5.9L, Vin Z, Eng Cfg V8 *
Vacuum Check Valve
- MISSING CHECK VALVE Vacuum Check Valve
Bob Parra
September 06, 2007 1999 Dodge Ram 1500 Pickup, 5.9L, Vin Z, Eng Cfg V8, USA/Canada *
Vacuum Check Valve
- UPDATED CHECK VALVE Vacuum Check Valve
Aamco Center 43050
June 22, 2009 2001 Dodge Ram 1500 Pickup, 5.9L, Vin Z, Eng Cfg V8 *
Replaced Vacuum Check Valve
- check valve Vacuum Check Valve
Jim Cruse
August 07, 2009 1996 Dodge Ram 1500, 5.9L, GAS, Vin Z, Eng Cfg V8 *
Replaced Vacuum Check Valve
- check valve Vacuum Check Valve
Eric Anderson
September 11, 2007 1997 Dodge Ram 1500, 5.9L, GAS, Vin Z, Eng Cfg V8 *
Vacuum Check Valve
- vac valves Vacuum Check Valve
Rick Eakins
November 24, 2009 1998 Dodge Durango, 5.9L, Vin Z, Eng Cfg V8 *
Repositioned HVAC Vacuum Hose
- vacuum line at vacuum t was pushed too far into check valve not allowing enough vacuum to go to switch HVAC Vacuum Hose
Nick Berry
January 25, 2010 1998 Dodge Ram 1500, 5.9L, Vin Z, Eng Cfg V8 *
Repaired HVAC Vacuum Hose — Found a broken HVAC vacuum line under the dash board. HVAC Vacuum Hose
Bob Pierson
September 15, 2008 1998 Dodge Ram 2500, Quad Cab 5.9L, Vin 6 *
Check Valve
- bad vacumn check valve on intake manifold Check Valve
Sabrina Luedke
July 01, 2006 1998 Dodge Ram 1500, 5.2L, Vin Y, Eng Cfg V8 *
Vacuum Hose
- THE VACUM LINE FROM MANIFOLD TO VACUM SWITCH UNDER WIPER COWL Vacuum Hose


Reply
0
HouseCallAuto

JCalvin70 4/29/2010

This is a very detailed answer. Take a shot at my question with the same eye for detail. It probably is easy for you to find a way to add a light to my Dodge diesel truck. Thanks for giving it a go.

HouseCallAuto

Momosapien 7/24/2010

Wonderful answer HouseCall. I am going to print this and try to trace my blower fan issue with your tips. I have spent several hunderd dollars at a few 5 star dealerships only to be told that I must have a short somewhere and that it will be several hundred, to over a thousand dollars more to trace it down and repair it. One dealership actually tried to charge me $120 bucks to replace the HVAC blower fuse. Not once has anyone made any reference to a possible vaccum problem. Thank you.

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