my Defroster Debacle
 

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.

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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.

Re: my Defroster Debacle
 

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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.

Re: my Defroster Debacle
 

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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).

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
 

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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.

Re: my Defroster Debacle
 

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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.

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.

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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.

Re: my Defroster Debacle
 

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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.

Re: my Defroster Debacle
 

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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.

Re: my Defroster Debacle
 

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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). ;)

Re: my Defroster Debacle
 

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.

Re: my Defroster Debacle
 

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.

Re: my Defroster Debacle
 

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

Grant

Re: my Defroster Debacle
 

I thank you too. Great thread !!! :metal::metal::metal:

Re: my Defroster Debacle
 

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

Re: my Defroster Debacle
 

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.

Re: my Defroster Debacle
 

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

Re: my Defroster Debacle
 

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.

Re: my Defroster Debacle
 

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.

Re: my Defroster Debacle
 

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

Re: my Defroster Debacle
 

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

Re: my Defroster Debacle
 

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...

Re: my Defroster Debacle
 

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

Re: my Defroster Debacle
 

its like a nail, i used pliers

Re: my Defroster Debacle
 

if mine breaks i am selling my truck or moving to fla.. i'll file this but i hope i don't need it.. great documentation..

Re: my Defroster Debacle
 

Success!!!! :b69:

Couple of things I learned:

- A universal and a couple of extensions made short work of the dreaded firewall nut

- The rod that the door pivots on slides out...mine was stuck because of the heater core leak and I spent about 30 mins thinking there was something holding it in.

- I turned my blend door accuator upside down to make the vacuum lines hook up alot easier...otherwise, I would've had to do some modifications Don't know why the port is at 2 o'clock...the one I took off (Delco) had the port at about 10 o'clock

- Don't attempt to hook up the threaded rod thing on top until you have your a/c on and the door is closed. If you do it, you'll likely to end up with a broken white thing like the pic above

- ATTACH THE A/C-HEAT CABLE BEFORE YOU PUT IT BACK IN THE FIREWALL. Just because it would've been much simpler...trust me


All in all this is one :devil: of a right up!!!! Thanks for the info and pics...they certainly served well today!!!

Re: my Defroster Debacle
 

Ah, it's been a helluva day. Just bought a sweet little 87 swb for a great price and went to fix some issues. This thread was a big help with some of the issues. First, no high on fan. O'reilly sold me the wrong high relay, but it turned out it didn't matter. If you have problems ithe the high on the fan, look at the junction block on the drivers side firewall. There are two studs, the fan direct attaches to the left one. Make sure it's solid! Mine was melted and loose, leading to erratic performance. New terminal and moved to the right post and wha-la! Fan on high! Still no defrost. Check defrost door with mity-vac, works great. Giant gap in main-to defrost duct, put round foam in firewalll side, aluminum duct tape other three sides. Better, but still weak. Check blend door, AH-HA! Door works, but little white plastic clip is broken. Where can one get the little white clip dealie?

Re: my Defroster Debacle
 

Ah, a little hunting got me this:

http://www.classicparts.com/1983-85-...ctinfo/68-248/

Thanks again all!

Re: my Defroster Debacle
 

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

Re: my Defroster Debacle
 

Crazeetxn- sorry I missed your PM earlier, I'm glad to see you guys got it all figured out!

Re: my Defroster Debacle
 

Thanks for this write-up and Pics. Helped me see how to replace my blower switch!

Re: my Defroster Debacle
 

Going to try to bring some life back to this one... First of all, thanks for the excellent write-up! Wish I had found this before I took on this project with my 86 K10. A couple questions on replacement parts... Any idea where I can find the black clip in the third pic?
Also, I was thinking the rod for the flapper popped out of the heater box... I ended up breaking the housing trying to pop it out instead of appropriately sliding it out.

It's looking like the junkyard is about the only place I am going to find a new heater box... Does anyone know some super-secret place the sells them new? I'm at my wits hunting for a new one.

Re: my Defroster Debacle
 

Nebk10 - the clip you asked about appears to be the same on my 75. So you should be able to go to a 'u pull it' type place and find a suitable replacement.
What I find odd is the difference in how the example and mine are assembled. Wonder if some PO or mechanic reassembled one of them wrong or if GM changed how they went together at some point?

Also, for those whose hot-cold adjustment is hard to move, I found the best place to put a drop of oil was where the cable lever slides behind the control assembly. Oiling the end of the cable shown in the pic made little difference. Sorry, didn't take a picture while I had that open.

Re: my Defroster Debacle
 

A home made fix for the blend door actuator plastic piece that was broken on mine. I had read this thread before pulling this out to replace the heater core and discovered the broken plastic piece which explained why the air was coming out everywhere. Rather then trying to find a new piece, figured it would be about as easy to make one out of some small bits of scrap metal, and a lot faster then waiting for a replacement part to arrive. (The weather was really nice while I was replacing the core and threatening to quit being nice, I don't have an inside repair place.) Pic1 shows the two holes I drilled in the door. Pic 2 shows the two metal replacement parts I made using the plastic piece as a pattern. They started as a flat piece of metal. I cut with a plasma cutter but a thin metal jig saw blade should work as well. A vise and suitable hammering gave the 90 degree bend. Since they are out of sight, pretty really doesn't matter. Used the original pin to attach the vacuum pot. Pic 3 is the silicone seal job to both provide an air seal and help hold the pin in place. The little black clip that held it in place escaped.

Re: my Defroster Debacle
 

There are minor differences through the years. Like the controls, they all work the same, but they are different enough you need to keep within the same family to swap stuff or outright change to a different generation setup.

In another thread somebody mentioned one of their vacuum lines disappeared INTO the box, others claimed this was not so, turns out mine has the same vacuum line that disappears into the box. (there is a slot on the top edge that a red rubber hose disappears into, its attached to the plastic vacuum lines that make up the typical hvac vacuum line spaghetti. When I yank out the plenum I'll find out how its nested in there, but since winter is here I am going to ignore that project for a few more months.

Re: my Defroster Debacle
 

Thanks for the replies everyone! The plastic i broke is not the white plastic retainer, but the entire outer housing (the heater box). This is the part I am going to have to replace, as it is definitely not fixable. If I haven't figured it out by the time I get back home next week I will post a pic when I do get back.

Re: my Defroster Debacle
 

Great write up! I don't think I could have accomplished this chore with out it. Bravo!

Re: my Defroster Debacle
 

my rig is all torn apart right now. i might as well go deeper and check out the hvac. i know its not working right...
thanks for the great write up!

Re: my Defroster Debacle
 

Gotta love the photobucket extortion going on.

Anyone have pics they can post of this process? My temp lever won't go all the way to cold. I'm wondering if something built a nest up in the fan housing somewhere....