AC/Heat stuck in front vent position
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AC/Heat stuck in front vent position - 4/16/2008 7:11:55 PM
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ride_da_lightnin
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ok 1998 Blazer...A few days ago I heard a small vacuum leak coming from behind the dash, so I took off the cluster and I could see where the leak was coming from...The position control switch, I took off the vacuum cluster that is connected to the switch and noticed that there was suction coming from the black vacuum line only...I also noticed that when accelerating the suction goes away but when I let off the gas it returns...Is there supposed to be some other suction or air blowing out one of the other colored lines? I did get another actuator and plugged it in, and nothing changed...no matter what position the switch is in...it doesnt change anything....I dont think it is the switch upon inspection but thought I would ask you all for an opinion...Thanks
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RE: AC/Heat stuck in front vent position - 4/16/2008 7:14:33 PM
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swartlkk
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Black line is the vacuum supply line to the HVAC control head. The mode changes made by you to the control head direct vacuum to the appropriate vacuum actuators in the dash. Run a search for 'vacuum actuator' or something similar and you should come across the diagrams and logic tables for both the automatic and manual HVAC controls.
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RE: AC/Heat stuck in front vent position - 4/16/2008 7:29:37 PM
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ride_da_lightnin
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Thanks for the reply kyle, I am not sure what you mean...I did a search and all that came up was topic about the 4wd actuator...I did buy a new "mode actuator" and plugged in the electrical plug and that didnt help me...I am sorry could you explain more? Thanks
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RE: AC/Heat stuck in front vent position - 4/16/2008 7:49:33 PM
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ride_da_lightnin
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Ok, so what part would you think I should replace? The schematic seems real confusing. I am pretty sure it is not the position switch...Thanks
*Combining Consecutive Posts*
I also dont have a problem with the temp setting..I get both hot and cold, just cant switch position.....
*EDIT by swartlkk* - Please use the edit feature to add additional information to your post if another member has yet to reply. Thanks!
< Message edited by swartlkk -- 4/17/2008 3:51:04 AM >
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RE: AC/Heat stuck in front vent position - 4/17/2008 3:52:16 AM
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ride_da_lightnin
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I would assume I have manual as it is a knob...How can I tell?
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RE: AC/Heat stuck in front vent position - 4/17/2008 9:07:18 AM
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swartlkk
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If you had auto, you would set it to a temperature, not just a color (red/blue) and you would have an 'Auto' position for the mode and the fan.
So I would go through the logic chart, verifying that you have vacuum to the appropriate ports on the back of the control head when in the various modes. If that checks out, then I would inspect the lines to the individual actuators. You may need to disconnect the lines at each actuator as well.
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RE: AC/Heat stuck in front vent position - 4/17/2008 7:38:21 PM
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ride_da_lightnin
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Ok it's manual and no matter what position the switch is in, the only suction is coming from the black vacuum line....like I said the heat control works just not the position...sorry i am being such a pain....thanks
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RE: AC/Heat stuck in front vent position - 4/17/2008 7:58:49 PM
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swartlkk
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If you can leave the black line hooked up, then feel for vacuum on the other ports, you should be able to use the logic chart to determine if your control head is working properly. If it is not, then the first thing I would do is replace the head.
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RE: AC/Heat stuck in front vent position - 4/17/2008 9:29:33 PM
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ride_da_lightnin
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Well when I leave it hooked up all I can hear is the vacuum leak of the black line trying to suck in,....as i change the switch from any position...nothing changes...the only vacuum is the black line..
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RE: AC/Heat stuck in front vent position - 4/18/2008 4:33:06 AM
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swartlkk
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If, with only the black line hooked up, you do not get vacuum on any of the proper ports (as defined by the pictures in the post I linked to above), then you have an internal fault in the control head.
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RE: AC/Heat stuck in front vent position - 4/18/2008 8:16:29 AM
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ride_da_lightnin
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There is a vacuum cluster that plugs into the position switch...no matter what position the switch is in, there is suction only coming from the black line...there is no air being sucked in OR out of any other lines in this cluster other than the black...when i turn the switch to floor, defrost, vent, ac, nothing changes....when i plug in that cluster of vacuum lines, nothing changes...just get the hissing sound
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RE: AC/Heat stuck in front vent position - 4/18/2008 10:47:32 AM
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swartlkk
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Ok... I think I see what the problem is here... I didn't think I needed to spell it out like this, but...
You need to keep the black line connected to the back of the HVAC control head, everything else gets disconnected. The black line is the supply line from the engine to the control head. If you have to make up a short piece of vacuum hose to keep it connected, do so...
Then use the logic chart to see if the ports have 'vac' when they are supposed to depending on the mode you have the hvac control module set to. You will then start the truck and check for vacuum per the logic chart. If nothing gets vacuum, replace the control head as I have instructed as there is an internal failure of the valve inside the head.
If, while you are checking this, when you cover the proper vacuum ports (that state VAC on the logic chart for the selected mode) with your fingers, and the hissing sound stops, then you either have a broken line or a failed actuator which will require further trouble shooting (more jumper hoses, etc).
I recommend that you print out the vacuum routing diagram and the logic chart for easy reference while you are performing this diagnosis.
< Message edited by swartlkk -- 4/18/2008 10:54:32 AM >
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RE: AC/Heat stuck in front vent position - 4/19/2008 3:30:40 PM
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ride_da_lightnin
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Thanks kyle..I just replaced the control head and that was the problem...I also have SES light on...It's the P1153 H02S Insufficent Switching Bank 2 Sensor 1. Which oxygen sensor is this?
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