A/C Housing Repair

A big part of auto restoration is deciding which parts to restore and which parts to replace. If you have a very original numbers-matching vehicle, it makes sense to redo as many of the original parts as possible. If you're restoring a car that's been modified or rebuilt with different parts, then reproduction parts are a good way to go. However, there are some parts that aren't being reproduced and are very difficult to find—at least in better condition than the parts you already have. A good example is your air conditioning housing or "suitcase" as it's commonly called. Many are made out of fiberglass and are frequently broken during the engine changing process. As soon as there's a hole in the A/C suitcase, exhaust fumes and other engine-compartment odors can be circulated through the heating/air conditioning system, making the vehicle unbearable to drive.

Prep
For most early vehicles, finding a replacement means scouring the salvage yards for the correct car, then removing the suitcase (not a fun job). Fixing the A/C suitcase you have may be easier than you think. Prior to injection molded thermoplastic, fiberglass was considered the "wonder" material by carmakers. Light, strong, and a good thermal insulator, fiberglass is also the enthusiast's best friend because of its ease of repair. All you need are some fiberglass mat and resin, plus a grinder and dust mask, and you're ready to make your A/C suitcase as good as new. A word of caution however, if you're working on a 100-point restoration, we recommend you find a suitable replacement. Repairing an A/C suitcase will restore the integrity of the part; however, the textured gray appearance will be altered in the process.


We are restoring a late-'60's GM A-body convertible into a nice, everyday driver, so we decided to repair the suitcase ourselves. Besides, the damaged area is actually behind the cylinder head, so the repair won't be visible. The first step is to grind a border around the hole approximately 1-inch wide and feather it down to the edge of the hole. Fiberglass resin, when it cures, forms a waxy film on the surface. You need to grind that away for the fiberglass repair to bond to the old fiberglass. Beveling or tapering this area allows you to build up several layers of fiberglass mat without making the repair stick up too high.

Finish
After the area around the hole is prepared, cut several layers of mat, matching the size and shape of the ground out area, then decreasing in size to that of the hole. We used three layers of fairly heavy mat to repair our two holes. With normal masking tape, we made a backup for the new fiberglass mat. Use several layers of tape and apply it tightly to the suitcase. Next, mix up a batch of resin and hardener and thoroughly soak the mat with resin, then lay it over the hole. Quickly soak the two successive layers of mat and put them in place before the resin begins to harden. Wearing gloves, we used our fingers to squeegee out the excess resin and air bubbles, and smooth the contour of the patch. Not only did we have holes to patch in our suitcase, but we had some fairly long cracks in the fiberglass as well. With a die grinder, we made a V-shaped cut in the cracks before we mixed the resin, so the patch adheres better. After applying the fiberglass mat over the larger holes, we poured the excess resin into these cracks.


After the fiberglass patches had cured (it took about an hour), we began shaping the repaired areas with 36-grit sandpaper, then 80 grit sandpaper. You can add more fiberglass mat and resin to the low areas and repeat the process or use plastic body filler. We got the surface fairly close with the fiberglass, then switched to body filler for the finishing touch. After the body filler, a couple of coats of primer (sanded with 180 sandpaper) got rid of the deep sanding marks. We selected a charcoal gray enamel to replicate the A/C suitcase original color. It took us about five hours to make this repair, but the finished result was worth the effort.