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20th Annual Technical Forum: A/C Refrigerant Hoses

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Q: How do A/C refrigerant hoses differ from coolant hoses?

A. Refrigerant hoses on the high side of the A/C system (the discharge hose between the A/C compressor and condenser, and the hose from the condenser to the evaporator) operate at much higher pressures than coolant hoses, anywhere from 150 to 300 PSI or more depending on ambient temperatures (the higher the outside temperature, the higher the internal operating pressuring inside the A/C system). So, refrigerant hoses must be reinforced and strong enough to handle such high pressures. By comparison, a typical radiator or heater hose usually operates in a range of 15 to 18 PSI.

 Refrigerant hoses on the low side of the A/C system (the suction hose that returns refrigerant from the evaporator back to the compressor) typically operates in the 10 to 50 PSI range.

 Hoses on both the high and low sides of an A/C system must also be highly impermeable so refrigerant vapor can’t seep through the microscopic pores in the hose material over time. On late-model vehicles with R-134a refrigerant, the A/C hoses have a special “barrier” liner inside to minimize refrigerant loss. The inner layer of neoprene is usually backed with a layer of nylon to stop refrigerant migration. R134a molecules are smaller than those of R-12, so the tendency to leak through hoses is potentially greater.

On older vehicles (1994 and back) that are being retrofitted from R-12 to R-134a, replacing the original hoses with barrier style hoses is recommended, especially if the original hoses need to be replaced anyway due to age deterioration or leaks. The hoses on older vehicles with R-12 A/C systems will usually tolerate R-134a without any problems. Over time, compressor oil seeps into the hoses and forms a barrier of its own that minimizes refrigerant loss. But considering the age of most of these vehicles, the hoses are probably getting hard and brittle and should be replaced to reduce the risk of leaks and refrigerant loss.
When the refrigerant hoses are changed on a retrofit application, bead-lock fittings are recommended because barbed fittings can damage barrier-style hoses. O-rings and seals also may have to be replaced with ones that are R-134a compatible.

Q. Should A/C hoses be replaced after a compressor failure?
A. Metallic debris that is spewed into the A/C system when a compressor fails can block orifice tubes and possibly damage a new compressor when it is installed. Getting all of the debris out of the system is therefore essential to make sure the new compressor won’t suffer the same fate.

Most of the garbage ends up in the condenser, but it can migrate from here to other parts of the system or be thrown backwards into the suction hose from the compressor’s intake port. Serpentine-style condensers with large diameter tubes can usually be cleaned by flushing with an approved flushing chemical. But parallel flow condensers or those with very small tubes may be impossible to clean, requiring replacement to get rid of possible contaminants.

As for the refrigerant hoses, replacing the suction and discharge hoses should not be necessary provided they can be thoroughly flushed and cleaned. Hoses that contain mufflers or orifice tubes, however, usually cannot be cleaned and must be replaced.

Installing a protective screen in the end of the suction hose that attaches to the compressor and/or installing an inline filter to trap any residual debris that may have been missed also is recommended for added insurance against a future compressor failure. 

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