AC/Heater Question-'70 C20 w/ Factory AC

[Kirk52]

After reading many posts here I am finally starting to figure out which vacuum line goes where and where each cable control connects to but I am somewhat perplexed about the cable that goes thru the firewall and attaches to a flat 90 degree rod that goes down into the evaporator/ heater core area on the engine side of the firewall. When I slide the heater control cable there does not seem to be enough movement in this rod to be able to control anything. Even when trying to move it by hand it seems partially "frozen". I would love to see the end down in the box but don't know how to get to it. How can I see what this rod connects to and whether or not it is working as it should?

Thank you

[68c10airstream]

Hi Kirk52, that cable through the firewall is for the blend air door (flap). When you move your dash control from cold to hot/hot to cold this cable moves back and forth to change the air from going completely through the heater core or completely through the evaporator core or blending anywhere inbetween those two extremes. Good luck, Brian Fuller

[Kirk52]

Thank you Brian for your response. How much travel should that rod make when the slide is moved all the way in either direction? When i turn it by hand it will only swivel about 1/2 inch or less. Does that seem about right?

[SS Tim]

If you don't have a service manual you might download one. There is a lot of information in it on the heating and A/C system (46 pages).

[Bigdav160]

What Brian said. There is a door connected to that shaft. IIRC, it only moves about 40º but is prone to rusting and debris that keeps it from moving.

[68c10airstream]

Hi Kirk52, i have my ac box apart for cleaning and repairs/repaint/reseal. I mocked it up to measure the hot/cold lever travel and full travel measures 1 1/4". This blend door is known for the rubber to let loose from the metal paddle, and i would assume it would affect travel. Someone on here repairs this door i believe. This ac box is held together with small rivets around it's perimeter, easy to drill out and remove. This blend door is obviously on the engine side of the firewall, fairly easy to unbolt from firewall and take apart. If this is a working truck with a ac system charged and working it will be a little more difficult to remove from firewall, but i think doable without removing the refrigerant. Some small clamps around the evaporator pipes that attach it to a metal brace that is riveted to the shell. Worse case scenario would be to drill out this brace rivets to get more movement. If i was doing it for the first time make it easy on yourself and remove the hood first, remove the rh hood hinge,(mark it's location), remove the blower motor, remove heater core hoses, remove engine side evap box clam shell bolts and seperate the box exposing the evap core. Now remove the remaining evap/blower case, evap pipe clamps, etc, and move the box slightly towards the passenger fender, and remove. If additional freedom is needed, then drill out the brace rivets mentioned earlier. This all sounds bad but if you work on vehicles sometimes it really isn't terrible. I think if you open it up you will find dirt and debris, mouse goodies, etc and possibly a rusted metal panel inside that could use some attention. Good luck, Brian Fuller

[Kirk52]

Brian that sounds pretty complicated. I don't know if I want to tackle that or not. I don't guess there is any way to see it from the cab side if I take the heater box off from around the heater core is there? And as long as I'm asking questions about heat and A/C, the vacuum actuated flap under the cowl, which way does it rotate on its axis? I assume it must rotate clockwise but I'm not sure. I installed a new one as the old one was broken (can't find the spring that attaches to it) but I can't seem to turn it either way by hand.
Anyway thank you for helping me.

Kirk

[Andy4639]

Here are a few pictures for you.


2 line vacuum hook up.




Three line hook up.

[Kirk52]

Thank you Andy4639, the photos were very helpful but they bring up another question, my AC/Heater control has 3 vacuum ports but the vacuum lines are set up like the 2 port system. A single vacuum line leaves the port under the dash and tees off twice so that the kick panel, hot water valve and cowl vent all seem to work off the same vacuum port. The other port goes to the vacuum source. Evidently one of the vacuum ports is not functional or is supposed to be plugged.

[Andy4639]

If it's not hooked up I would plug it off.

[Corndog777]

Hey Andy thanks for the pics, I have similar problem, but I have 3 ports on the control.
I have plugged and still can not get enough vac to open kick panel valve as well as the outside are on top of dash.
Any ideas?

Bill

[Andy4639]

Check the vacuum source. Make sure you have the correct vacuum hooked up to each one. There are different ones depending on where they are located.
Some apply the vacuum to close off and some open up when applied.

[Corndog777]

Thank you! I ran it just like the picture... Not sure if it worked yet... Having problems with defective. Fuel pump