Orifice Tubes, Expansion valves & TXV's - Auto A/C Diagnosis & Troubleshooting Help from the world leader in auto A/C information!

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Your best source for complete troubleshooting and diagnosis information on auto A/C systems. Our information provides proper repair, recharge, service and maintenance procedures for all automotive air conditioning systems. Regardless if you have a current CCOT (cycling clutch orifice tube) system or an expansion valve and POA valve system, we've got the information you need. From step-by-step help on retrofitting and recharging to complete A/C compressor or component replacement, our A/C manuals provide you a quick and easy methods that have been proven helpful to everybody from the apprentice to the professional.

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auto air conditioning orifice tubes and expansion valves utilize very small openings to meter the flow of freon in your system. Be sure you know how to keep these valves clean and flowing! Find out more now! Orifice tubes and expansion valves (commonly called Thermostatic Expansion Valves or TXV's) both perform the same function in auto air conditioning systems, they just look a little different. These components provide a restriction in the flow of refrigerant. That restriction causes the refrigerant to change from high pressure liquid freon into low pressure liquid freon before it enters the evaporator. Have a closer look at the different designs and how they function.

Location:
Typically, expansion valves (TXV's) will be located at the inlet of the evaporator.
Block type valves will have both the inlet and outlet (liquid and vapor) of the evaporator passing through the valve. The conventional design expansion valve will be mounted on the inlet (liquid line) only.

On the other hand, orifice tubes (also called fixed orifice tubes or CCOT- Cycling Clutch Orifice Tube Systems) could have the orifice tube located in a variety of positions. As shown on the right, the orifice tube could be located at the EVAPORATOR INLET, mid way between the EVAPORATOR and the CONDENSER (in-line) or at the CONDENSER OUTLET.

Orifice tubes and expansion valves restrict the flow of refrigerant through the system. Although they both reduce the pressure of the liquid refrigerant, they are designed differently and can be located in a variety of spots on the auto A/C system.
Typical locations of expansion valves and fixed orifice tubes.

See photos of orifice tube location here

As a general rule, Expansion Valves and Orifice Tubes are serviced by replacement. In some cases, where an expansion valve is manufactured to include an inlet screen, the inlet screen may be removed and cleaned to restore proper flow of refrigerant to the system. Orifice tubes likewise fail because of debris and corrosion being caught up on the inlet screen. However, as they are usually a low cost item, it is generally accepted that they be replaced rather than cleaned, therefore assuring that debris is eliminated from the A/C system.

A Close up look at the Orifice Tube:
Originally introduced on GM applications in the 1977 vehicle model year, orifice tubes have become far more popular and are used by several manufacturers.

Typical auto A/C orifice tube illustration shows the inlet screen, orifice and outlet screen! Get complete auto A/C system information, troubleshooting, service and repair manuals at the COOL ZONE!
A typical orifice tube. The inlet (red side) includes a fine screen to protect the actual orifice (illustrated in yellow). The outlet portion
(blue) also includes a filter screen. O-Ring seal(s) separate the
high pressure side from the low pressure side of the system.

The design appears simple because there are no moving parts. The internal brass orifice (illustrated in yellow on the left) is the actual opening that the refrigerant flows through. The inlet screen is in place to protect the orifice tube from getting plugged up with any debris that may be in the system. Is the design fail safe? You be the judge of that!

See up close photo of actual orifice tube here!

The concept of the orifice tube is great. By contrast, expansion valves rely on moving parts to open and close the valve opening, thus metering the flow of refrigerant into the expansion valve. Additionally, expansion valves may have external 'temperature sensing' devices know as capillary tubes. Just another part of the valve exposed and subject to damage.

With an orifice tube, the flow of refrigerant through the valve (tube) is constant. Overall flow throughout the A/C system is controlled by cycling the A/C system compressor on and off as required. The end result remains the same; there is a controlled amount of refrigerant entering into the evaporator.  

Historically, the biggest problem with orifice tubes is that they tend to easily get plugged with debris that may be traveling throughout the A/C system. As soon as the flow of refrigerant through an orifice tube is restricted, the flow of oil (which travels throughout the A/C system in the refrigerant) is also restricted. That becomes the start of catastrophic compressor failure.

What's wrong with these orifice tubes?
How can you help prevent this?
Auto A/C orifice tube photo shows serious restrictions! How can you prevent this from happening? Install an in-line A/C filter from the COOL ZONE! As stated above, orifice tubes can easily become restricted with debris that may travel through the system. Restricting the orifice tube immediately restricts the flow of refrigerant. It also limits the flow of refrigerant oil. The oil is required to maintain compressor lubrication. Therefore, orifice tube restrictions can easily cause a catastrophic compressor failure. Auto A/C orifice tube photo shows serious restrictions! How can you prevent this from happening? Install an in-line A/C filter from the COOL ZONE! What causes the debris and contamination? In short, moisture which enters the system mixes with the refrigerant to form acids. Those acids corrode aluminum components. That corrosion moves throughout the system and get caught by the filter screens on the orifice tube. As shown on the left, if takes less than 1/10 of a teaspoon of debris to plug the orifice tube.

How can you prevent plugged orifice tubes like this?

 

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