A Much Needed Modification

Third Gen Evaporator Airbox.



I was having a problem with airflow thru the interior ducting in my 91 TA. I had suspicions that it was a clogged Evaporator Core, rather than the blower, as I replaced it about a year ago with an OEM unit. It turns out I was right. I suspected the Evaporator had never been cleaned, even though the maintenance on this car was "top-notch" before I purchased it. The Evaporator is easily overlooked unless it leaks.



The Evaporator core was extremely dirty, clogged with debris and old foam, as was the “condensate screening” on the output side of the Evaporator core. As of this writing I also cleaned out and resealed the ducting behind the dash. Airflow has returned post cleaning.



The problem with periodic cleaning of the Evaporator is that in order to do it easily, in reality, you have to evacuate the A/C system and remove the Receiver/Dryer, so that the upper part of the Airbox can be removed without damage to it and other components in the area. The way GM designed it, the entire Airbox has to be unfastened from the firewall to easily access the Evaporator.



I was having none of that. I convinced myself that I could remove the upper Airbox/Evaporator Cover without breaking into the system or removing the Receiver/Dryer. The problem is that the rear flange of the top of the Airbox is actually under the lip of the Cowl and the forward end surrounds the Receiver/Dryer connections, so you’re screwed. I attempted to spread the forward end out enough to clear the tubing, and although I got it off and was able to do the Evaporator cleaning, I cracked it in two places fore and aft. I stop-drilled the cracks, reinstalled it, and applied “four-season” tape over the top, convincing myself I was going to do better.



I purchased another top cover from an Ebay seller, and planned my modification. I decided to cut the cover in half longitudinally, for ease of future removal.



Materials required:

Piece of .060 Kydex sheet, cut to 2.5” X 7.75”. (Available Amazon and other places.)

Quantity 12 “Christmas tree” small plastic automotive “push fasteners.” (See photos, Amazon.)

VHB tape



Tools required:

Shear or utility knife

Drill Motor

#40 Drill

#30 Drill

Unibit

#40 and #30 Clecos and Cleco pliers

Dremel with cut-off wheel

File

Clamps

“Four Season” tape



Process:

• After receiving the replacement top cover, although it was what I expected, the plastic was kind of whitish (probably from age and/or sunlight,) than the one in my car. I washed it with some purple power and a toothbrush, then, when dry, took a heat gun and restored the plastic “back to black.”
• Using my shear, I cut a piece of Kydex to the proper dimension. I chose the 2.5” width so it would fit inside the two vertical stiffeners on the firewall flange. (circled in red.)
• After cutting the Kydex patch to size, I marked the location, and using the Unibit, drilled an 11/16” hole to go around what is either a “boss” as a result of the plastic molding process, or an attach point for an accessory not utilized on the Firebird. (circled in yellow.)
• I laid out for 6 fasteners on each side, (overkill, I know,) approximately 3/8” inboard of the edges of the Kydex patch.
• Since the top is curved, I applied VHB tape to one side of the Kydex, and taped it into place.
• Then I drilled a #40 hole on each end, and installed the Cleco fasteners.
• Then I “rolled” the Kydex patch around the top of the box cover, used 2 small Vise Grip clamps, and drilled 2 holes fore and aft on the other side.
• Drilled the remaining 10 holes to #40, installing Clecos as I went along.
• Once all the holes were drilled, I opened all the holes up to the final #30 size, and then removed the Kydex patch and de-burred all the holes.
• Note: The “Kydex patch” and airbox top should be completely fitted and drilled prior to cutting the Airbox in half to assure proper installation.
• Using the Dremel and small cut-off wheel, I cut the Airbox top in half and deburred it.
• My original Airbox top has some kind of molded white thin foam glued on the “screen side/output side” of the cover that the replacement did not. I was able to transfer it and glue it into the replacement top.
• I used black butyl seam tape on the firewall and mating surface (top to bottom) flanges, (with a “dry release” agent) and installed the patch with the push fasteners.
• Applied a small bead of “four season” tape to the forward edge.
• Looks really good, and although not “factory or original” it will be a lot easier to service in the future.
  
  
  
  
  
  
  
  
  

 

I applaud your resourcefulness and creativity and I like your end result. I'm sure some purists will take one look and be horrified. Some will probably even sneer and claim you have somehow damaged the structural integrity of your car (e.g. every fuel access hole thread). Others will claim you have irreparably destroyed whatever value your car had.
But those of us who are not snobs will like it.

 

@Aaron R. You crack me up!
Just so happens I AM one of those purists! LOL!
As a matter of fact, over the Memorial Day Weekend, I changed the fuel pump the right way....

The difference is that one you cut a hole for the fuel pump, you are messing with the structural integrity of the car, (especially in a Vert,) and after cutting the hole the car can or be easily restored to its original appearance/condition.

I can restore it back to "as built" condition in a matter of 5 minutes, by replacing the Evaporator top cover, and no one would ever know.
in fact, I bought two covers, just in case my first modification attempt failed, which, however was unlikely.

 

In that case I am shocked and appalled that you would stoop to such levels of degenerency. Your car is now utterly worthless and you have betrayed your people. Literally anyone who looks to buy it will immediately know the airbox can never be original again. Not to mention the structural integrity of your airbox, entire a/c system, and everything else under the hood has been compromised. Pretty much a ticking time bomb. Do the world a favor and drive that car straight to the crusher, then proceed with extreme prejudice.

 

A most excellent diatribe!

 

Nice work. I dealt with a few of these A/C "service issues" on vans while at GM. This will be much easier to clean, disinfect and replace if/when needed,