A/C Heater Diverter Door Function

Discussion in 'Interior Restoration' started by K1ng0011, Aug 26, 2018.

  1. K1ng0011

    K1ng0011 Veteran Member

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    I have a 1972 base model camaro that came from the factory with AC. I noticed that I had a small heater core leak. So the last two days I took it upon myself to replace the heater core since winter is coming up. It was not an easy job. I did get it replaced and it seems to be leak free. However, when I took the heater box out from under the dash I noticed something. The plastic clip on the door was broken. So my vacuum pod on the back of my heater box still worked but the door would no longer move. Probably been broken for a long time. I had to WD-40 the door to get it moving properly again. I did fix it and tested with a vacuum pump to make sure all of the vacuum pods are working and that the door is working before reassembly. I was wondering what the A/C Heater Diverter door does exactly. When I had the heater box out I was looking at it. Looking at it it looked like it had three positions. Halfway open/closed which is the position it was stuck in when I pulled it out since the plastic clip was broken. The other two positions are operated by the vacuum pod on the back. They seem to direct air to the heater core and toward the defrost or bypass the heater core and direct air out the vents. Can anyone confirm what positions this door is supposed to work on the heater controls and its exact function?


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  2. K1ng0011

    K1ng0011 Veteran Member

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    I am going to put on an ac delete case on my firewall. In the meantime I have my evaporator case out I was able to test the functionality of the a/c heater diverter door with a vacuum pump. Technically the a/c heater diverter door consists of two doors mechanically linked together the dash vent door and the ac heater diverter door. On your control panel while you are in Heat, Defog, Defrost it blocks all air out your dash vents. The door to your dash vents is closed. It also directs all airflow from your heater core to the other end of the case for floor and defrost vents. When on Bi-Level or Vent no vacuum is applied and the door is in a half open/half closed state. So some air can get out the dash vents and some can get out the floor vents/defrost vents. When on Max A/C or Normal AC it directs the maximum amount of air out the dash vents. Airflow to the floor vents and defrost vents is closed. Please keep in mind that the blend door is pushed to the cold to provide maximum visibility for the AC heater diverter door in all of the following examples. Hopefully this is helpful to someone at some point in the future if they want to restore, repair, or verify that everything is working properly.

    HVAC Airflow: Air goes through the cowl vent (if its open), then down to the heater/ac blower motor. The blower motor pushes the air through the evaporator. After going through the evaporator air goes through the blend door. This is the cable controlled door which is connected to the hot/cold lever on your HVAC controls. The blend door diverts air between the heater core and ac/heater diverter door. The blend door is to blend the heat/fresh air/air conditioned air. The ac heater diverter doors responsibility is direct air to the dash vents or toward the other end of the heater box for air out your floor vents or defrost vents.

    Heater AC Controls:
    Heater AC Controls.JPG

    Heater AC Ducting:
    Heater AC Ducting.jpg

    Dash Vent Door (Mechanically linked to AC Heater Diverter Door):
    dash vent door.jpg

    AC Heater Diverter Door:
    ac heater diverter door marked.jpg

    Blend Door:
    Blend Door Marked.jpg

    HVAC Controls in Defrost, Defog, Or Heat Position Door Positions:

    AC Heater diverter door in heat position.jpg

    dash vent door.jpg

    HVAC Controls in Bi-Level or Vent Position (No Vacuum Applied to AC Heater Diverter Door Valve):

    AC Heater Diverter door default position no vacuum.jpg
    Dash Vent Door No Vacuum.jpg

    HVAC Controls MAX AC or Normal AC:

    AC Heater Diverter Door AC Positions.jpg
    Dash Vent Door AC Positions.jpg
     
  3. Popper

    Popper Veteran Member

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    Thanks for the write up! I have been going back and forth between sticking with the stock AC or going Vintage Air, basically either spending $50 or $1500. I like the clean firewall look w the VA however i also like the idea of having the option of a stock system. I charged up my stock AC a couple of months ago properly and it never really cooled the car down. Vent temps would come down a few degrees but cabin (or vent temps) never got cold. The Evap would get cold, compressor cycled properly and gauges read proper pressure so i know the AC was working. I ended up taking the internal box out and found that the vacuum pod in the case was rusted shut and was affecting the AC heater diverter door functionality. I fixed the vacuum pod so i am going to try the stock system again with the pod now working properly. I still may end up going with the Vintage air system but at least i can try the stock AC with some certainty.

    At a minimum cooler weather is coming so my plan is to go VA next Spring if the stock AC isn't adequate.
     
  4. K1ng0011

    K1ng0011 Veteran Member

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    I am no AC expert but if you are using R134 refrigerant you will want to have a parallel flow condenser, from what I have read. If you do not you may not get the low temps you are expecting. I have seen people complain about the air flow out our vents in our cars. It is very important that you have the evaporator case sealed to the firewall your heater box under your dash sealed properly and all of your vent ducts sealed. If they are not the air can escape and you will get less airflow from your vents. Turn your blower on max and feel around to see if you cant find any airflow leaks. Also make sure your evaporator is not clogged with debris.

    AC Car MAX Heat from Dash Vents

    I also found something else out for anyone reading this post in the future. If you have your controls set to heater you dont really get any air out of the front dash vents in our cars. The air is directed to the floor and the defrost vents. If you have an AC car with the AC system not functioning. Set your controls to MAX AC or Normal AC and move your temp slider to heat. You should get a lot of heat from your dash vents. Like you would expect from a modern car.

    20181018_155954.jpg
     
  5. Coadster32

    Coadster32 Veteran Member Lifetime Gold Member

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    Digging this thread out from the past...

    First...thank you for this and the other threads you have on this topic....it is the future, and I can't be the only other one to read it so, thank you.

    I do however have a couple/few question still on this topic. I pulled the suitcase off the firewall, and planning on an A/C delete panel. I still intend to use the blower motor, as it still works, and a lot of the wiring is still intact. (up to this point, didn't use any of the ventilation system...T-top car). I am looking for expectations on air flow if I can't get the vacuum system working,

    If I keep the passenger side kick panel door closed to the cowl, (no vacuum), should I expect it to continually draw fresh air from the cowl area? In other words, is this vacuum door opening used for recycling the air in the cab?

    The two doors are mechanically tied together...Should I be able to tell if the dash vent door is working along with the A/C heater door by feel of the hand through the firewall by the blend door? I read where sometimes the clip gets busted off.

    The blend door...is this vacuum driven as well? I could position it in any fashion I choose, but not certain yet which would be best. If I left it 1/2 open, (or taken right out), would I get enough airflow at high speed to move air everywhere?

    I know there are more vacuum driven flappers to direct the air...just want to see what might be best. I will try first to see if the vacuum system is functional, but have the heads off the engine as well, and don't want to get too deep into this right now. I hope to revisit in the winter. Just thought perhaps I can "rig" something for now, as it will be better than what I had previously.
     
  6. Twisted_Metal

    Twisted_Metal Administrator Staff Member Lifetime Gold Member

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    If I'm not mistaken... The "Blend Door" is the one which is cable operated and connected to the Hot/Cold" lever of the HVAC control panel.

    All of the other doors are vacuum controlled and their position depends upon the position of the selector switch on the HVAC panel.

    As noted above, the Dash Vent Door is Mechanically linked to A/C-Heater Diverter door. (And the Diverter door is vacuum controlled.)

    The Fan(blower) and A/C compressor is electrically operated.

    There were some differences, over the years, in how this system works but I don't know the exact details.

    I only know the selector on the HVAC panel had a different number of positions depending upon the model year.

    My 80 HVAC panel is similar to the pic in the earlier post but it does not have a "Defog" position. (The Fan control is also reversed, with "HI" at the top instead of the bottom.)

    Your 79 is probably the same as mine.
    upload_2020-8-6_16-7-20.jpeg

    I’ve never had to troubleshoot that part of the system so some of it is still a mystery to me.

    The previous posts provide the best description I’ve seen of the various functions and positions of the doors involved.
     

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