First thing’s first – what’s an orifice tube? An orifice tube is a device placed in a high side line of a mobile A/C system that creates a calibrated restriction, dividing the high side from the low side. As you can see from the picture below, it also acts as a filter to catch any debris (and, in this case, probably some stop-leak as well) and keep it from making its way back to the compressor.
If you’re doing an A/C system repair, you should really consider replacing the orifice tube. Clutch cycling orifice tube systems control the evaporator core temperature by cycling the A/C compressor clutch on and off, regulating the system pressure. Other systems use a TXV or Thermal Expansion Valve to control refrigerant flow (though these systems also cycle the clutch if the pressure get too high or low). Rarely does a vehicle have both flow control devices. As we learned earlier, the orifice tube acts as a filter as well as creating a restriction in the system to create a low pressure area where the refrigerant expands and changes state from a liquid to a gas, cooling the evaporator core to around 32-36ºF (and subsequently the air in the cabin). Over the years, small pieces of the compressor and material from the accumulator may enter the system and become trapped by the orifice tube. When this happens, the refrigerant is more restricted than it should be and it places an extra load on the compressor in addition to reducing cooling efficiency.
There are special tools for removing an orifice tube, but I’ve always had pretty good luck using small needle nose pliers and carefully twisting them out. Happy wrenching!
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