Question about 1997 Chevrolet Astro

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Switch will not change from defogger to other vents. What are possible problems and solutions

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If it was me the first thing i would do is check all of the vaccum lines under hood and the ones behind the control unit itself try these website to see if they have your car listed www.autozone.com if they do you be able to get pictures and diagrams also try this website its www.alldatadiy.com i also would like to give you this information if you every have any hard to find GM- parts its Schram auto & truck parts 1-800-292-1032 and they website is www.schramauto.com wish you the best Michigan Man.

Posted on Jun 25, 2009

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Sounds like the blower motor actuator which is vacuum driven. You most likely have a vacuum leak, preventing the actuator from switching from defrost to vent. Check under the hood and start at the firewall (usually on the passenger side) and with the blower on high, look for a possible vacuum leak. Best of luck.
Greg

Posted on Jun 25, 2009

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Wiring diagram for rear window defogger 2005 silverado from dash to deffoger


Rear Window Defogger System Components
The rear window defogger system consist of the following components:
• HVAC control module
• Body control module (BCM)
• DEFOG relay
• Rear window defogger grid
Rear Window Defogger Operation
When you turn the ignition to the ON position, ignition voltage is supplied to the DEFOG relay coil. Battery positive voltage is supplied at all times to the DEFOG relay switched input. When the rear window defogger switch is depressed, the HVAC control module illuminates the rear window defogger indicator and sends a class 2 message to the BCM. The BCM energizes the DEFOG relay by grounding the control circuit of the relay. This allows battery positive voltage from the relay switched input through the switch contacts and out the relay switched output to the rear window defogger. Ground for the rear window defogger is provided by G306 or G390 (crew cab).
When you turn ON the ignition and press the rear window defogger switch for the first time, the defogger cycle lasts 10 minutes. Further operation results in 5 minute defogger cycles.

Do you know what your messing with ? What's the problem ?

Oct 30, 2016 | Cars & Trucks

1 Answer

My heater only works some of the time and my rear defrost dont work what could be the problem


As by heat only works some of the time , you mean it doesn't blow air out of the vent's . This means you probably have a problem with the blower motor or blower motor resistor or blower motor relay .
Rear Window Defogger Inoperative

    Exchange the rear defogger relay with a known good relay from the under hood junction block.
  1. Turn the ignition switch to the ON position.
  2. Press the rear defogger switch to the ON position.
Does the rear defogger grid warm?
--
Yes Go to Step 2
NO Go to Step 3

2

Replace the faulty relay.
Is the repair complete?
Go to Defogger System Check --

3

  1. Use a fused jumper wire in order to backprobe between terminal A4 of underhood junction block connector C3 and ground.
  2. Use a test lamp in order to backprobe between terminal C5 of underhood junction block connector C3 and ground.
Does the test lamp light?
--
Go to Step 4
Go to Step 23

4

  1. Use a test lamp in order to backprobe between terminal C5 of underhood junction block connector C3 and ground.
  2. Press the rear defogger switch to the ON position.
Does the test lamp light?
--
Go to Step 5
Go to Step 14



Mar 23, 2016 | 1999 Oldsmobile Alero

1 Answer

Front defogger will not blow


sounds like the mode switch has gone bad and needs replacing.the mode switch is the one that changes the direction of air flow from defrost to dash to floor. if nothing has blocked the vents to the window then this is what it sounds like.

Jan 31, 2014 | 1998 Volkswagen Beetle

1 Answer

My 2004 6cfl. Trailblazer rear window defroster is not working. The wires appear to be making a good contact. The outside mirrors defrost ok using the same switch as the test window defroster. Is there...


There is a module that controls the rear window defogger grid . LGM/ EGM Liftgate or endgate module .Receive's message on class 2 serial data network from the HVAC control module to turn it on when button pressed . Fuse # 3 30 amp located in the rear fuse box . Do you know where the rear fuse box is ?
Rear Window Defogger Description and Operation
Rear Window Defogger System Components
The rear window defogger system consist of the following components:
• HVAC control module
• Liftgate module (LGM)/endgate module (EGM)
• Rear window defogger grid
Rear Window Defogger Operation (With LGM)
Battery positive voltage is supplied through the LGM 2 fuse to the LGM for the rear window defogger system. When the rear window defogger switch is depressed, the HVAC control module illuminates the rear window defogger indicator, and sends a class 2 message to the LGM to enable the rear window defogger. The LGM enables the rear window defogger by allowing battery positive voltage to the rear window defogger.
When the rear window defogger switch is pressed for the first time, the defogger cycle lasts 10 minutes. Further operation results in 10 minute defogger cycles.
Rear Window Defogger Operation (With EGM)
Battery positive voltage is supplied through the EGM 2 fuse to the EGM for the rear window defogger system. When the rear window defogger switch is depressed, the HVAC control module illuminates the rear window defogger indicator, and sends a class 2 message to the EGM to enable the rear window defogger. The EGM enables the rear window defogger by allowing battery positive voltage to the rear window defogger.
The following conditions must be met for rear window defogger to operate:
• The end gate glass position is not below the index position.
• The window express down movement is not requested.
• The window down movement is not requested.
If the end-gate glass is not fully closed, the DIC displays "Tailgate Glass Down" when the rear defogger operation is attempted.
When the rear window defogger switch is pressed for the first time, the defogger cycle lasts 10 minutes. Further operation results in 10 minute defogger cycles.

Fuse Block - Rear
Beneath the left rear seat

Jul 13, 2017 | Chevrolet TrailBlazer Cars & Trucks

6 Answers

Hyundai XG350 rear defogger doesn't work. I have changed the relays, checked all the fuses all good, dash switch works because I changed that too. checked the wire to the grid thats' ok too. now what?


The rear defogger is controlled by the Electronic Time and Alarm Control Module (ETACM). It receives a signal from the switch, and if the car is running, turns on the rear window defogger. Most frequently the problem is a blown 30A defogger fuse. Other common problems are the defogger switch itself or the switch not being plugged in properly, but there can also be a bad defogger relay, defective ETACM, or wiring issue. If you're capable of doing some electrical diagnosis, I'd encourage you to register for a free account at www.hmaservice.com (requires Internet Explorer and Adobe SVG Viewer) and print the schematic from the site. Also, does the indicator lamp come on when you depress the defogger button,I hope this help you in the right direction now you know how it works

Feb 12, 2010 | Hyundai XG350 Cars & Trucks

1 Answer

My turn signal noise is still on sometimes after i've turned, my brights don't stay on, keyless entry not working,and rear defrost not working.


TURN SIGNAL PROBLEM IS THE THE MULTIFUNCTION SWITCH.KEYLESS ENTRY REMOTES NEED NEW BATTERIES.THE DEALERSHIP WILL CHANGE REMOTE BATTERY AND REPROGRAM DOOR LOCKS.CHECK REAR DEFOGGER FUSE AND RELAY.IF BOTH GOOD.YOU HAVE A FAULTY DEFOGGER SWITCH OR OPEN IN THE GRID.YOU CAN BUY A GRID REPAIR KIT AT AUTO ZONE OR ADVANCE AUTO PARTS AND OREILLYS.

Jan 31, 2010 | 2004 Pontiac Grand Am

1 Answer

I have a 2007 Endeavor with the following problem: Air does not blow out of the front defogger to defog the windshield. You hear it blowing, but it is not coming out. I have switched the knob to change the...


The air flow is controlled by an actuator behind the dash. The part is sometimes called the heater control box. When you are selecting the air flow to change from the a/c controller. The signal is not being received to the actuator. The actuator is called the blend door.
You need to have the air /blend door actuator change. I think in this car is the air recirculation door. Same thing different name .

Good luck

Oct 31, 2009 | 2004 Mitsubishi Endeavor

1 Answer

Strong radiator smell when defogger or heat is on


if our floor wet and fog in the window and when you wipe it off its nt easy to remove like oily its our heater core that broken sorry pierre

Mar 03, 2009 | 1994 Chevrolet S-10 Blazer

1 Answer

Rear defogger


The switch is part of a timer module that controls the rear defogger grid on the glass, they fail and create the problem you described, replace the module.

Oct 01, 2008 | 2001 Saturn L-Series

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