my Defroster Debacle

[85gmcguy]

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.





Heater blend door actuator- 28.79
A/C and heater control switch- 6.98
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.

[85gmcguy]

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. Once those are gone you have to remove the heater/defrost and a/c ducting (items 1,2, and3) 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).With it removed, duct 1 can be freed from below the column and wiggled out of the way. The last photo is the view with all ducting removed.

[85gmcguy]

First picture shows approximate location of the studs sticking through the firewall (arrows). 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. The cable from the dash control that operates the heat flapper must also be disconnected (picture 3).

[Blake_H]

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!

[85gmcguy]

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. Note the position of the flat "tang" on the end, it only goes back in one way. The pin in the fourth picture goes through the end of the "blend door actuator". 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 find, remove them all. The last pictures shows the halves being separated.

[85gmcguy]

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. Second picture shows heater core mounting- it's only three screws. 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.

[85gmcguy]

Originally Posted by Blake_H

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!

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.

[85gmcguy]

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. With the selector in COLD (picture 2) I adjusted the cable so that the door was completely closed (picture 3). With the selector in HOT (picture 4) the flapper should be fully open (picture 5). Note exposed heater core.
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.

[85gmcguy]

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.

[85gmcguy]

While the heat selector cable was disconnected, I unhooked the connectors, removed the light, and pulled out the control unit. (picture 1). The fan switch (picture 2) is a simple matter of one screw, then it slides out. The vacuum valve is held by 2 screws, picture 3 shows the bottom view, picture 4 shows it from the top. 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.

[85gmcguy]

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.


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

[rayfinseats]

Great info. I don't see why they made it so complicated. Is all that ducting necessary? Do you think the heater would get hot enough to melt wiring? I am setting mine up all toggle switches and was thinking a choke cable for the flapper door.

[85gmcguy]

Originally Posted by rayfinseats

Great info. I don't see why they made it so complicated. Is all that ducting necessary? Do you think the heater would get hot enough to melt wiring? I am setting mine up all toggle switches and was thinking a choke cable for the flapper door.

The ducting feeds the defroster vents and dash vents, the heater is basically just the default, it feeds out to the floor. I don't think the heater gets hot enough to melt things, but it would kinda depend on your thermostat. Choke cable (or similar) would most likely be fine for flapper door.

[Gyawo]

This will help me out tons! Thank you for posting it on my thread(Dash "cage").

Grant

[rayfinseats]

I thank you too. Great thread !!!

[flamingbig10]

nice write up Gary I wish I had the patience to fix the factory air in my truck but it was missing every a/c part under the hood, and all the vacuum lines and the vacuum operated pieces so I ripped it all out

[rayfinseats]

Question: If I hook a positive 12v wire to the one lead on the heater blower motor on my 83 it should come on right ??? Cuz mine don't.

[motornut]

Good info it answers some FAQ
Should work ,ive done it with an aligator clip...check the ground or do your own
Posted via Mobile Device

[85gmcguy]

Originally Posted by rayfinseats

Question: If I hook a positive 12v wire to the one lead on the heater blower motor on my 83 it should come on right ??? Cuz mine don't.

That would be my basic understanding. The wiring for the motor feeds through resistors located on/in the heater box to provide speeds below "high". If it fails, you only get "high", so I'm guessing the motor is shot. Shouldn't be expensive but will probably be a major PITA to change.

[BLE 'BURBAN]

Originally Posted by rayfinseats

Question: If I hook a positive 12v wire to the one lead on the heater blower motor on my 83 it should come on right ??? Cuz mine don't.

The housing the heater blower motor mounts into is fiberglass so if you don't have a grond strap going from at least one mounting bolt/screw for the blower motor to the fire wall, then you'll get NADA . If'n you do and the motor doesn't go into hyperdrive when you jump it directly to the battery then yeah the Heater Blower Motor has gone 10 toes up.

[rayfinseats]

Thanks guys. I was pretty sure but just wanted to check. It's grounded and looks pretty easy to change.

[crazeetxn]

WOW! Awesome write up! Found it off another thread...unfortunatetly, mines about to get ripped out too.

[crazeetxn]

Question...the pin that the blend door pivots on, how the heck did you get that out? Does it just "slide" out? That things giving me more fits that the bolt on the firewall.

Thanks for the info...

[rayfinseats]

The cable PULLS to open the flapper door and PUSHES to close? Correct?

[motornut]

its like a nail, i used pliers