Hi all,

I'm doing the 4th gen dash swap into my 3rd gen firebird (1991). The car is currently fitted with an LT1 engine so wiring isnt a problem for me. However, I have been scratching my head over this HVAC ducting issue that everybody seems to have. I'm taking my time with this one, because I want everything to work properly, all air pressure the way it should be, no leaks, no incorrect air routing, etc.

It's 845pm so I will have to wait until tomorrow to get the pieces I want to experiment with but I wanted to throw out my idea here and see if anyone
has tried this before. In any case, I will definately report back after I've tried this and let everyone know how it went.

I wanted to get a good look at the setup in a 4th gen tonight so I looked on ebay. I found one with a picture. From what I see, it looks like the entire system is contained within itself. AC coil unit for cold, heater core for hot, and blower motor. It looks very rectangular and looks like it may fit in the 3rd gen in place of the original air setup under the passenger dash, with the exception of the AC unit attached to the back of it which could be relocated in the future with air ducting.

My plans are this:

Removing the entire original assembly from the inside-firewall side of the 3rd gen. This includes removal of the heater core.

Obtaining the self-contained setup from a fourth gen. I've attached a picture of the setup.

Judging by the picture, it looks like the blower fan is on the right, and it gets it's air supply from right above. I am going to buy an air filter of the closest size and cut it to fit over this. Then construct a duct to the port on the firewall that goes to the outside world (possibly use the hole that was for the 3rd gen blower fan)

The Heater core ports are to the left of this, these ports could be hosed to the location of the original heater core, or new holes could be drilled into the firewall at a location closer to the actual heater core.

All the servos could be wired to a 4th gen cluster controls in the same manner as they were in the 4th gen car. I hear it is a big pita to get these controls working with the 3rd gen air setup for people doing these dash swaps. Everything would be fouth gen, therefore it should all work properly together.

If AC does not exist, then the big unit on the rear can be removed and a plate can be constructed and screwed in to block off the orfice. If AC is existing in the car, this unit can be moved elsewhere and air-ducting can be run to collect the cold-ness from this unit when the AC is on.

Does anyone have any ideas or improvements for my idea? I'm going to be trying this tomorrow so I will let you all know how it turns out. I'm hoping it works. I don't want any sacrifices or compromises with the dash swap. I want everything to work right.

This board has helped me alot the last few months so I would like to give something back to the community. Hopefully I will have good news for all of you tomorrow and maybe this thread will help some people in the future.

 

Well, it didn't get to go as I wanted it to...

For one, the 3rd gen dash isn't as deep as the 4th gen so there is no room for the blower motor to exist under the dash, even if I had cut a hole in the firewall to accomodate the AC coil unit. Also, the AC coil unit doesn't unbolt in itself. The mounting for the blower motor comes with it And I can't even dremmel it off to bypass it because of the way the air routes.. it's alot to explain.

What I did end up doing was removing the blower motor/AC Coil plastic and
seeing about fitting the orfice that went to that to the hole in the 3rd gen firewall for the heater core. It looked like it would sit right so I bought some foam padding and set it up. I made 2 brackets to hold it in. It's in nice and tight now and I will use the AC delete heater box on the engine side of the firewall to get the air flow going... Hopefully everything will work out. I took some pics with my camera phone so if things work out I will definately post them here.

Has anyone attempted anything similar to this approach?

 

I am sticking with my idea above, I've got the airbox mounted next is the dash to the airbox. However, I am curious; Has anyone ever tried mounting the 3rd gen air ducting dash piece to the back of the 4th gen dash and cut the orfices back far enough to allow using flexible ducting to connect them to the actual vents on the 4th gen dash? If anyone has, how did it work out?
If I run into a wall I may try this, but I am sticking with my original idea until I see if it will work or not.

What other approaches have you people taken and successfully conquored this obsticle?

 

i guess out of 106 people that viewed these posts nobody has overcome this obsticle.

 

i dont have a/c in my 86 so i cant help you there, but i did use the 4th gen heating ducts, and i just cut the 4th gen one to match the holes on the 3rd gen one, then put foam around the edges to keep the air in, and air comes out the vents so im happy.

 

Have you done any searches?? 95% of people who do the swap and keep HVAC just cut the 4th gen ducting to fit the 3rd gen box.. You're trying to re-invent the wheel. The only issue left is the 'blend' mode the 3rd gen didn't have is an extra defrost setting.

Kevin D.

 

Agreed. I also used the 4th gen air box, a dremel, and some foam from the 3rd gen hush panels to seal the sides. Works just as it should. Still have an electrical issue to sort out and that hot/cold cable though ...

 

ALOTE of people on here went overboard with the ducting made one simple hacksaw cut and glued foam and it matched perfect with no leaks and full blow power. No need to repull the dash to check or anything.. but then again maybe im just that good

 

The two don't match up as perfectly as people make them out to... but yea... hack on that one piece and they will work. Like said, you just have to add foam and some tape action to the one big piece and it will be good enough to flow air.

The top duct doesnt match up well without cutting and the lengths of the middle sized ducts don't match up perfectly either. Both will result with loss of airflow unless fixed:


End up cutting the piece to look similar to this, but I cut mine a little too much:


This is the gap if you cut it like I cut mine. I obviously need to add more foam when I put the dash in for good:

 

Don't forget when the dash is in you can check for air leaks and add foam and duct tape where its needed,

 

I went the 4th gen box way - It just looked too odd to me to make the 3rd gen box fit the 4th gen dash. It came out pretty nice. I'll explain here to give people who are attempting the same swap an idea of my solution that I came up with, so I can get the gears going in your head

The first thing I did was make the airbox for the 4th gen flat and straight instead of curving back. I did this by cutting a piece of metal and using bolts and spacers to hold it up, then I added foam to seal the sides. Look at the pitures.

I then made custom brackets to bolt it against the firewall. I had to use the dremmel to alter the flow opening a little bit. Also, note that you will have to dremmel a little bit of metal on the little pouch area on the upper right corner of the dash to get the 4th gen airbox to seat at the proper location.

Attached are some pics showing what I did. Any questions shoot them at me.

-R

Also, to seal to the firewall, i used stick on padding weathersealing tape - i got it from home depot. Good stuff. I also got a smaller roll to pad the square on the outside where I cut the notch for the heater core lines. It all worked out well. If anyone needs to know what hoses i used or the heater core to route towards the water pump (front of the engine), let me know, I dont know the info now but the hoses are still new enough that I can look next time I go to the car and get the number for you and you can get the same hoses from autozone