Barrier Hose Upgrade - Griffiths

Would you believe that the typical Porsche 911 we are working on has nearly 40 feet of rubber air conditioning hose? In contrast, a 930 has 43 feet. The design of the air conditioning hose dates back to the 1960s. Why is there so much hose? The air conditioning compressor is located in the rear, while the evaporator, drier, and front condenser are situated in the front. Additionally, there is a primary condenser at the back. Consequently, the hoses have to run back and forth, covering a significant distance.

The main issue with the stock A/C hoses is that they constantly leak refrigerant. For every linear foot of A/C hose, there are a certain number of parts per million of refrigerant that leaks out slowly. The leak rate per linear foot is so small that refrigerant dyes cannot penetrate the refrigerant hose because the dye is suspended in the refrigerant oil. Furthermore, electronic refrigerant sniffers fail to detect these minor leaks, as they are not sensitive enough. If the detector were sensitive enough to identify such tiny leaks, it would likely trigger false alarms from other nearby substances. Therefore, what you have are thousands of tiny leaks spread across long hoses, which combine to create a significant loss.

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Considering these facts, if we revisit the time when this car rolled out of the factory fully charged with refrigerant, it was only a matter of time, usually a year or two, before it required a top-off or addition of more refrigerant—year after year. In those days, it wasn't a big issue since R12 only cost $1.75 per pound, and we were unaware of ozone depletion, which leads to increased harmful UV rays.

With the revelation that certain refrigerants, like R12, contribute to ozone layer depletion, a new replacement refrigerant called R134a was developed. The A/C industry conducted studies on system leakage, which concluded that a better refrigerant hose was necessary. As a result, new standards for refrigerant hose design were established, outlined in the SAE (Society of Automotive Engineers) specifications. This new hose is referred to as "barrier" hose, which features an additional liner (a non-plasticized nylon co-polymer) that reduces the permeation (leakage) rate of refrigerants.

Dupont, a producer of R134a, along with various hose manufacturers, conducted studies to compare leakage rates between non-barrier (traditional) hoses and barrier hoses. They labeled the leakage "permeation," indicating that refrigerant leaks through the wall of the hose. In these studies, sections of each hose type—30 inches long with a 5/8" ID—were filled to 80% of their maximum volume with liquid refrigerants (comparing R12 to R134a) and heated to 176°F. While they do not specify the pressure, we can speculate it was around 380 psi for R134a and 333 psi for R12, based on temperature/pressure charts (typical for an overcharged system or a very hot day). Most systems do not typically run at such high psi; a fair average pressure while the compressor is active would be 225-250 psi, while resting pressure would be around 100 psi.

The calculated yearly leakage rates indicated that R12 refrigerant lost about 1.5 pounds per year with non-barrier hoses and only 0.3 pounds per year with barrier hoses. For R134a, the losses were approximately 1.8 pounds per year with non-barrier hoses and just 0.2 pounds with barrier hoses. Clearly, non-barrier hoses result in significant losses regardless of refrigerant type. Naturally, the more frequently the A/C system is utilized, the greater the losses. For instance, there is a notable difference between the A/C usage patterns of someone living in Seattle compared to someone in Houston, as well as disparities between a weekend driver and a daily driver.

This is where the Dupont study becomes particularly relevant for 911 and 930 car owners. The study primarily focused on "front-engine" vehicles, which typically have all components (compressor, condenser, drier, evaporator, and connecting hoses) located close to one another. Conversely, a 911 or 930 has components spread out, necessitating 40-43 linear feet of hose. The Dupont study projected leakage based on a standard car with only 6 to 10 feet of hose. A typical front-engine car has about 9.2 cubic inches in internal hose volume or 60 square inches of internal surface area. In contrast, a 911 has approximately 66 cubic inches of hose volume and 621 square inches of internal hose surface area.

Thus, the difference between an average front-engine car and a 911 is substantial:
Front-engine car = 21 cubic inches, 178 square inches of surface area
Rear-engine 911 = 66 cubic inches, 621 square inches of surface area
The 911 manifests a 214% increase in cubic volume and a 249% increase in hose surface area, which significantly impacts permeation rates.

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Reduced permeation is especially critical with R134a refrigerant, as its molecules are smaller than those of R12, and system pressures are somewhat higher, making old-style hoses more susceptible to early leaks. Furthermore, the construction of this new type of A/C hose is more forgiving during flexation. The A/C hose lines in the 911 have some bends, and thus, barrier hoses are an ideal solution.

We removed all five of the 22-year-old A/C hoses and installed a new Griffiths barrier hose set. The process of removing the A/C hoses is straightforward and does not require a car lift. In fact, the entire Mr. Ice Project was completed using a simple rolling jack and jack stands for support. It is best to replace one A/C hose at a time with a new barrier hose. Although the task of replacing the entire A/C hose set is time-consuming—averaging around 8 hours for a DIY enthusiast on the ground and a few hours less with a lift—it is absolutely necessary. It would be unwise to achieve lower vent temperatures one day, only to discover the following week that the increase in temperatures is due to not replacing the original leaking A/C hoses.

Replacing the A/C hoses is not complicated; there is no need to remove the engine or the car's interior. Upon completing the project, we created a "how-to" instruction set that logically guides one through the process. Here’s a brief overview: There are three A/C hoses in the engine compartment: the compressor to the evaporator and the rear condenser to the front condenser. Two of the hoses exit from slots near the rear shock towers and travel further to their respective components. Notably, the compressor to the rear deck lid condenser hose is one of the easiest to replace. Additionally, two hoses are located behind the driver's side front tire—one from the drier to the front condenser and the other from the drier to the evaporator. The rear condenser to front condenser hose also passes through this area. All A/C hoses are secured to the body with clamps and screws. We simply removed each hose, temporarily reattached them for easy identification of the mounting points, and then reconnected the original clamps while installing the new barrier hose set. Almost all hose fittings have nuts that are measured in inch increments (e.g., 3/4", 7/8"), allowing the use of standard non-metric wrenches.

In this installation, with the Kuehl Fender Condenser we designed, we have six refrigerant hoses, compared to the original five provided with the car. Although there will be a slight increase in the total length of the hoses, we will have reduced hose weight and volume due to the size and type of hose used. Additionally, we will be utilizing less refrigerant! We will delve into the "less refrigerant" concept later on.

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