The Fox-body Mustang has become the new ’32 Ford, the original hot rod, in that you can almost build one from parts from the ground up. Almost every piece of the engine, transmission, interior, suspension, rearend, and brakes are available. Many Fox owners take advantage of the smorgasbord of parts offered, but for some reason, the A/C system often gets overlooked. Springtime is nice to cruise around with the windows open, taking in all the scents of the flowers blooming. That is, until summer comes back around. And you start sweating the moment you get in the driver’s seat.
By then, the easiest thing to do is just grab a can of Freon at the local parts store—the one with the hose attached to it—and squeeze the R-134a in until it blows cold-ish. You probably (definitely) overpaid for that fancy can; you know, the one that had the words “With Stop Leak” emblazoned across the front of it, just above the happy little snow man. Like you even know whether it’s actually leaking or not, huh?
Besides, what you really don’t realize is that R-134a refrigerant you’re squeezing into your Mustang’s R-12 system isn’t going to do the job properly, no matter how many of those overpriced cans you squeeze in there. And just because you bought that little “retrofit kit” off the shelf doesn’t mean you did a proper R-134a conversion. In fact, you just wasted your money. The frosty-the-snow-man can, conversion kit, and all. All of it.
So what’s the solution, you ask? Well, we have it, and it’s actually not as difficult or expensive as you may think. The correct way to upgrade your antiquated R-12 system to an R-134a system is an engine compartment upgrade kit, often called an underhood kit. It often consists of a compressor, condenser, accumulator, orifice tube (or expansion valve), and all connecting lines. The real beauty of the underhood kit is twofold. One, you don’t have to pull the dash out—everything is done under the hood. And two, it’s a proper conversion and is designed to work efficiently with the remainder of the existing components in order to freeze your butt off.
How It Works
Without getting into “science” or “theory,” the easiest way to understand why a proper R-134a conversion is necessary is that R-12 is a more efficient refrigerant. And therefore, R-134a refrigerant is not capable of providing the same cooling as R-12 in systems developed specifically for R-12 refrigerant. You probably already know that the compressor is the part of the system that mounts to the engine and is driven by the belt. It is a refrigerant pump, and pumps compressed hot gas through the discharge hose to the condenser. The condenser is the radiator-looking component that mounts directly in front of the radiator. It cools and condenses the compressed hot gas coming from the compressor into a cool, compressed liquid. There must be sufficient airflow across the fins of the condenser for it to work properly. If a fan isn’t working properly or if the fan shroud is damaged or missing, then the system will not work properly.
The compressed liquid travels through the liquid line to the orifice tube, which is in-line between the condenser and the evaporator. The orifice tube acts as a filter and as a pressure regulator. It regulates the cool, compressed liquid to flow into the evaporator as a low-pressure liquid. This low-pressure liquid is what gets cold and cools the air that passes through the evaporator core on its way to the vents, and ultimately, your face. (Technically, an A/C system doesn’t cool air, it actually removes the heat from the air, but we’ll save that for another time.)
This is the single most important step in the process, especially concerning the type of refrigerant being used. R-12 systems, like in a Fox-body, use a large tube-and-fin-style condenser, which works fine with R-12 refrigerant. Proper underhood kits contain a microtube-style condenser, which is much more efficient and better suited for R-134a
As the refrigerant flows through the evaporator core, it turns to a low-pressure, cool gas. As it leaves the evaporator, it collects in the accumulator (thus the name), where it waits to be sucked out by the suction side of the compressor via the suction hose, where the process starts all over again.
Al Sedita started Classic Auto Air in Tampa, Florida in 1982. Since its inception, CAA has been specializing in repairing and upgrading vintage and muscle car A/C, including Mustang. Since then, it has expanded to include not only factory-style systems, but also complete bolt-in systems for cars equipped with antiquated systems or no A/C at all. These “Perfect Fit” systems are ideal for street rods, kit cars, and pre-A/C era vehicles.
But CAA still offers factory A/C restoration parts, services, and upgrades, including underhood kits. This part of the company is called the Original Air group. Located in Tampa, Florida and headed by General Manager Tim Cordileone, Original Air provides A/C products and services for just about any year, make, and model. One of its specialties is the under-dash Mustang unit, which it restores to factory-new. It also restores condensers, evaporators, compressors, and control heads. You can even get OEM-style hoses to go with your refurb’d components.
One of the systems to Original Air’s catalog is the ’87-’93 Mustang underhood kit. The kit (PN 22-132) is a direct bolt-in kit for all 5.0L-equipped ’87-’93 Mustangs and sells for $775. The only major component you’re not replacing is the evaporator, and if you want to go ahead and do that while you’re at it, OA offers a complete kit (PN 22-133), which includes it for $850. The kit contains a Sanden-style compressor and adapter brackets, a direct bolt-in high-performance parallel-flow condenser, accumulator, orifice tube, pre-crimped hoses, and all necessary installation hardware. Basically all you need is some tools, three cans of R-134a, some time, and a Fox-body in need of some A/C help.
Our buddy Jason Weicht recently purchased a super-clean ’87 LX coupe with a 5.0L and a five-speed trans. This 80,000-mile notch is really clean and was completely stock, save for a set of Cobra R knockoffs and an aftermarket boom box. We couldn’t wait to get our hands on it to get some bolt-on parts installed, but first things first—the A/C wasn’t blowing cold. Upon closer inspection, one of those “retrofit kits” had been installed over the factory valves, and everything else was original.
Instead of trying to repair the system and track down some expensive R-12, we decided to just upgrade it. After checking for leaks, we determined the leak was in the condenser and the evaporator core seemed to be in good shape. So, instead of replacing the entire system (and pulling the dash), we went with Original Air’s underhood kit.
Before starting, we took the coupe to a local A/C shop, where we had them evacuate the old refrigerant properly. We don’t have an A/C machine, and that’s the only way to remove the old stuff correctly. Back at the shop, we tore into the install. The whole process took us about four hours, and the only specialty tools we needed were the A/C gauges and a vacuum pump. Luckily, we had those on hand. (If you don’t have them, you can pick them up at Harbor Freight for about $150 for both. Trust us, you’ll be glad you did.)
After disassembly and before we began installing the new components, we flushed the evaporator with denatured alcohol. We put an old vacuum hose on the end of a funnel and put the other end of the hose in the top tube of the evaporator near the firewall. Once full, we let it soak for about 30 minutes. Then, with a rag over the other fitting, we gently blew out the alcohol and leftover crud with compressed air. Ours was really nasty, so we had to do it twice. (You can find denatured alcohol at your local hardware store, and it’s not very expensive.)
Once everything was bolted on and the fittings were tightened, we vacuumed the system down and charged it up. It was about 80 degrees out by the time we fired it up, and even at idle, 40 degree air was coming out of the vents. If you get a 30 degree drop, your system is considered to be working properly, so our 40 degree drop made us quite happy, and chilly.
Classic Auto Air’s Original Air