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AC blend issue

This is a discussion on AC blend issue within the General Help forums, part of the LSx Technical Help Section category; I am fortunate enough to have an Ice cold AC. But it is very hard to enjoy it when the ...

  1. #1
    Chief of his tribe! LSCyaL8R's Avatar
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    AC blend issue

    I am fortunate enough to have an Ice cold AC. But it is very hard to enjoy it when the dash vents will only blow for minutes at a time. I feel rather certain that the issue lies somewhere in the blend door and how it is actuated. It seems as though the climate control needs to maintain vacuum in order to hold a particular vent setting. I say this because cycling through settings will allow me to enjoy my ice cold air for a few minutes until the blend door apparently closes and no air comes out anywhere, even though the blower motor sounds nice and strong.

    My question is. Aside from the main vacuum line coming from the engine, which obviously is at least attached, what other parts of the climate system can cause this symptom. Tonight after work I am going to look in the engine bay at this vacuum line and see it's condition... cracked? problem solved! if not i'll have to start tearing down the dash and looking in there, not something I look forward to doing..... I pose my question here so I at least can go in armed with a rundown of what to expect in there. I really gotta go buy me some shop manuals.... thats the next big project lol

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    TJEA Retirement Home Dr.Crash's Avatar
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    maybe its the switch it self

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    Moderator Firebirdjones's Avatar
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    It's a pain to diagnose. You'll need the GM shop manual to run you through it. I've never had to diagnose a 4th gen,,but I did recently have to do my truck for the same issue.

    If it's anything like that at all, it could be any number of things. The doors use a vacuum diaphram, that could be cracked and leaking. Any one of the hoses for the system could be leaking. On the dash switch itself that Crash mentioned,,,there is a vacuum control switch with 5-6 hoses going to it. The seal dries up inside the switch and renders the trap doors inop, or they work very slowly. These are notorious for leaking. Not sure if the 4th gen has one.
    This was the problem I found with my truck,,,problem is though the switch has been discontinued and no aftermarket suppliers carry it either
    I should hope the 4th gen won't be that way.

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    Chief of his tribe! LSCyaL8R's Avatar
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    I'm a rather inustrious young man so i would assume that repairing a cracked seal wouldn't pose too much trouble. But from hearing your description i would feel that this indeed is my problem. The car sat for 3 years being driven only once a week to keep the motor running well. The AC was dead when I got the car so its safe to assume that the switch hadn't been moved in years. I'll have to tear apart the switch and see if I can rig something to seal it better. my doors both move slowly and do not hold position so again the switch suddenly seems to be a prime candidate for my troubles. meh... i'll get to it this weekend some time and let you all know how it goes

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    Moderator Firebirdjones's Avatar
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    I haven't looked at one for a 4th gen but I would assume it would be like any other. They are not a repair type item, and can't be opened as far as I know, and probably take the risk of cracking the plastic. It's a throw away and replace type item.

    The one I worked on is a circular shaped piece that actually rotates as you move the switch. Wouldn't be hard to pull the dash assembly out and have a look though, might give ya an idea.

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    Chief of his tribe! LSCyaL8R's Avatar
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    Yeah I was kinda hoping the switch wouldn't be a perma sealed unit..... ugh. there is a junkyard with a unit from an 02 WS6 within driving distance from me. could prob pick it up cheap and be done with it..... till then i could always wedge the blend door in an advantageous position lol. It's really annoying when its humid and you have the top off and you can't feel the AC.

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    Moderator Firebirdjones's Avatar
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    Quote Originally Posted by LSCyaL8R View Post
    Yeah I was kinda hoping the switch wouldn't be a perma sealed unit..... ugh. there is a junkyard with a unit from an 02 WS6 within driving distance from me. could prob pick it up cheap and be done with it..... till then i could always wedge the blend door in an advantageous position lol. It's really annoying when its humid and you have the top off and you can't feel the AC.
    What I did temporarily on my truck is plug the hose to the A/C door into a hand held vacuum pump,,,so when I need the A/C I open the door with the hand pump. It works and gets me by until I'm able to locate the correct switch. So far it's a lost cause though.

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    TJEA Retirement Home Dr.Crash's Avatar
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    Quote Originally Posted by Firebirdjones View Post
    What I did temporarily on my truck is plug the hose to the A/C door into a hand held vacuum pump,,,so when I need the A/C I open the door with the hand pump. It works and gets me by until I'm able to locate the correct switch. So far it's a lost cause though.

    +1
    i have used the mighty-vac for many-a-things.

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    Moderator Firebirdjones's Avatar
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    Funny,,,,I drove the truck this morning to pickup a bike for my son. He decided he wanted the A/C on while driving,,,,I couldn't reach down to the floor and grab the vacuum pump so I just flipped the A/C on.

    It was blowing cold out of the floor while idling, cruising part throttle,,,but as soon as I would coast down a hill (high engine vacuum) it would overcome the vacuum leak at the switch and move the door,,,,blow out the vents until I hit level ground and start part throttle cruising again, then switch back to the floor again
    I have to find a stupid switch somewhere,,,,UGH!!!

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    Chief of his tribe! LSCyaL8R's Avatar
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    well before i got a chance to really tear apart my dash the dang thing started working just fine. i'm in no mood to really dive into dissasembling my dash so i will just chalk this up to dumb luck and enjoy my super cold AC! I'll venture a guess that the thing was just sticky from not being turned in about 3 years. after playing with it things may have set and now it switches fine. thanks guys!!!

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    Chief of his tribe! LSCyaL8R's Avatar
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    I spoke too soon..... to be continued.

  12. #12
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    Anyone out there might be able to use this info too. I did a search and didn't come up with much on this problem except for this post.

    My son and I both have an 01 and an 02 T/A and his 01 all of a sudden started having problems with his A/C Heat wouldn't change to the different positions, just the floor and defrost. Net is most of you probably know something wrong with the switch that redirects the vacuum to the right diaphragms to change venting direction, bad diaphragm, insufficient vacuum or no vacuum.

    Based on the way it's designed, been working on cars for 30 years, the design of the switch and the diaphragms are pretty good and unlikely to go bad. Although I pulled the glove box out and checked for vacuum inside the car at the 6 vacuum line connector. We had slight vacuum, but in my mind not enough to actuate any diaphragms.

    So a couple of things to start with, there's a main vacuum source connected to a "T" on the passenger side of the engine back towards the rear and at the top. The line at the top of the "T" goes toward the front of the car, the line on the "T" shooting straight back goes to the dash control and the line on the bottom is the vacuum source.

    One quick test is to pull the "T" out first, start the car and see if you have vacuum (hissing) coming from the bottom line. If not, trace it and see if it's become disconnected. If it does work, connect the bottom line to the one that goes towards the dash with a inline vacuum connector. If it works, great you've made progress. Follow the line that goes towards the front of the car on the passenger side.

    In the case of my sons car, we found the previous owner had let a battery go with a bunch of corrosion all around it. The acid had eaten is way through a wiring harness towards the front of the car by the battery where this vacuum line runs too. The interesting thing is they had the car repaired by someone who did a crappy job, key here is they did NOT repair the vacuum line and it got bad enough that it finally cracked. So we cut out the bad area, repaired it and we were in business.

    The net is, gotta have good vacuum for it to work properly. Hoping this info would help someone out.
    Last edited by torqhead; 07-11-2009 at 04:21 PM.

  13. #13
    Member DaddySS's Avatar
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    The vacuum line runs from the manifold, down to a reserve tank that sits inside the RF fender below the headlamp and then to the a/c controls. It's a good bet that the problem is more likely there than the control itself. Check those vacuum lines and I'll bet you find your problem.

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