Fixing the Defroster/Heater
 

My defroster quit working and I heard what sounded like a vacuum leak coming from the heater/defrost/a/c control unit in the dash. I started trying to track down the leak and before I knew it (actually about 2 weeks later) I had my dash completely ripped apart and my heater box laying on the garage floor. My handy-dandy "mity-vac" brake bleeder pump confirmed what I suspected- the "heater blend door actuator" was bad. If your defroster isn't working and your vacuum lines are OK, this could easily be your problem as well. They're a bear to get to because the whole box has to come out. I hit RockAuto.com to do some shopping.

http://67-72chevytrucks.com/gallery/...3/P1010279.jpg
Heater blend door actuator- 28.79

http://67-72chevytrucks.com/gallery/...3/P1010275.jpg
A/C and heater control switch- 6.98

http://67-72chevytrucks.com/gallery/...3/P1010276.jpg
A/C Vacuum control valve- 9.65

My fan switch has been broken for several years, it was functional but the knob wouldn't stay on. The vacuum valve was cheap insurance. I'll try to clarify anything if I can. Just ask.

Re: my Defroster Debacle
 

Ok, first thing is to get the dash pad and glove box removed. Be very careful not to rip the ducts loose from the dash pad.
http://67-72chevytrucks.com/gallery/...3/P1010341.jpg

Once those are gone you have to remove the heater/defrost and a/c ducting (items 1,2, and3)
http://67-72chevytrucks.com/gallery/...3/P1010335.jpg

May seem a little confusing, but stay with me. Duct 3 fastens to the heater box with 2 screws and to duct 2 with 1 screw and then slides down from under a clamp strip. With it removed, you can work on duct 2. It has a screw through the top of the metal dash holding it up (just above the center).
http://67-72chevytrucks.com/gallery/...3/P1010343.jpg

With it removed, duct 1 can be freed from below the column and wiggled out of the way.
http://67-72chevytrucks.com/gallery/.../P10103451.jpg

The last photo is the view with all ducting removed.
http://67-72chevytrucks.com/gallery/.../P10103371.jpg

Re: my Defroster Debacle
 

First picture shows approximate location of the studs sticking through the firewall (arrows).
http://67-72chevytrucks.com/gallery/...3/P1010349.jpg

Second picture shows actual studs on removed heater box. Upper left circle shows heater hose connectors. Please note- the heater hoses MUST be removed, they will not come through the firewall. (Ask me how I know). The white arrow is the "heater blend actuator". This is the new one. Should give you an idea of how tight to the firewall it really is.
http://67-72chevytrucks.com/gallery/...P1010305-1.jpg

The cable from the dash control that operates the heat flapper must also be disconnected (picture 3).
http://67-72chevytrucks.com/gallery/.../P10103271.jpg

Re: my Defroster Debacle
 

Nice write up! Thanks for the info and photos. It looks like fun. :)

I just did this to my Suburban, but I had to drop the fender and inner fender to get my box off the firewall.

How did you get yours out without doing that? I need to do my crew cab here pretty soon and would like to know.

Thanks!

Re: my Defroster Debacle
 

The heater box splits into two pieces. The plate (1) mounts the HOT/COLD cable, and is held by three screws. The mixer door is held in by and pivots on a pin (2) which must be removed.
http://67-72chevytrucks.com/gallery/...3/P1010303.jpghttp://67-72chevytrucks.com/gallery/...3/P1010300.jpg

Note the position of the flat "tang" on the end, it only goes back in one way.
http://67-72chevytrucks.com/gallery/...3/P1010298.jpg

The pin in the fourth picture goes through the end of the "blend door actuator".
http://67-72chevytrucks.com/gallery/...3/P1010293.jpg

The circled screws in photo five are under a foam seal which must be removed to access them. Keep it to put back on. The rest of the screws are easy enough to fin, remove them all.
http://67-72chevytrucks.com/gallery/...3/P1010304.jpg

The last pictures shows the halves being separated.
http://67-72chevytrucks.com/gallery/...3/P1010291.jpg

Re: my Defroster Debacle
 

First picture is the new actuator installed (red arrow) with the old one beside it (green arrow). The arm hasn't been switched over yet.
http://67-72chevytrucks.com/gallery/...3/P1010284.jpg

Second picture shows heater core mounting- it's only three screws.
http://67-72chevytrucks.com/gallery/...3/P1010283.jpg

Last picture shows old and new heater cores. I didn't even suspect a leak, but at just over 25.00 you could consider it cheap insurance.
http://67-72chevytrucks.com/gallery/...3/P1010281.jpg

Re: my Defroster Debacle
 

I'm not sure if they are different or not. The bottom stud is really close to the fender, but I got my (fairly large) hand to it. I didn't remove the fan box because I didn't need to for this project, but I could see having to remove the fender to get it out.

Re: my Defroster Debacle
 

Putting the case back together is pretty much the reverse of taking it apart. If you have a vacuum pump you can confirm proper operation before you reinstall it. The next few steps can be done with the assembly sitting on the floor of the truck.

First picture shows the adjustment point for the heat flapper door.
http://67-72chevytrucks.com/gallery/.../P10103271.jpg

With the selector in COLD (picture 2) I adjusted the cable so that the door was completely closed (picture 3).
http://67-72chevytrucks.com/gallery/.../P10103231.jpghttp://67-72chevytrucks.com/gallery/...3/P1010324.jpg

With the selector in HOT (picture 4) the flapper should be fully open (picture 5). Note exposed heater core.
http://67-72chevytrucks.com/gallery/...3/P1010325.jpghttp://67-72chevytrucks.com/gallery/.../P10103261.jpg

The ports on the new actuator are larger on the new actuator than the old one (picture 6), I made adapters from larger tubing and barbed connectors.
http://67-72chevytrucks.com/gallery/...3/P1010328.jpg

Re: my Defroster Debacle
 

Once everything is hooked up and adjusted, feed the studs and the heater core inlet/outlet through the firewall. I used my trusty helper (arrow) to hold it in place till I could get the nuts started on the studs. Make a last check to be sure nothing is between the heater box and firewall before you tighten it up. Attach your heater hoses and anything else you disconnected and you're good to go. Duct work installation is reverse of removal.
http://67-72chevytrucks.com/gallery/.../P10103311.jpg

Re: my Defroster Debacle
 

While the heat selector cable was disconnected, I unhooked the connectors, removed the light, and pulled out the control unit. (picture 1).
http://67-72chevytrucks.com/gallery/...3/P1010309.jpg

The fan switch (picture 2) is a simple matter of one screw, then it slides out.
http://67-72chevytrucks.com/gallery/...3/P1010306.jpg

The vacuum valve is held by 2 screws, picture 3 shows the bottom view, picture 4 shows it from the top.
http://67-72chevytrucks.com/gallery/...3/P1010308.jpghttp://67-72chevytrucks.com/gallery/...3/P1010307.jpg

Picture 5 shows the vacuum connector, there are 2 long legs with push nuts that hold it in place. The vac selector CAN be changed without pulling the controller, but it ain't easy.
http://67-72chevytrucks.com/gallery/.../P10103301.jpg

Re: my Defroster Debacle
 

Because I am also trying to get my A/C working again, I wanted to check out the evaporator. The circle in the first picture is what fell out when I removed it. Second picture shows just how nasty it was. It's since been cleaned and reinstalled. Almost ready to service it, just in time for warm weather.

http://67-72chevytrucks.com/gallery/.../P10103191.jpghttp://67-72chevytrucks.com/gallery/...3/P1010317.jpg

I hope this write-up helps somebody (anybody). ;)