Is the orifice tube on the low side?

No. The orifice tube in most automotive air-conditioning systems sits on the high-pressure side of the circuit, between the condenser/receiver-drier and the evaporator. The low side refers to the line from the evaporator outlet to the compressor intake.

In many passenger vehicles, the orifice tube serves as the fixed metering device that throttles high-pressure liquid refrigerant before it enters the evaporator, creating the necessary pressure drop for cooling. Some systems use a thermostatic expansion valve (TXV) or place the metering element inside the receiver-drier assembly, but the general rule remains: the metering device precedes the evaporator and is not on the low-pressure side.

Where the metering device sits in the A/C loop

Understanding placement helps diagnose cooling performance and pressure readings. The following points describe typical placement and flow direction.

• In most vehicles equipped with an orifice tube, the device is located in the high-pressure line between the condenser/receiver-drier and the evaporator.


• In some designs, the orifice tube is integrated inside the receiver-drier assembly, making that assembly the actual metering point.


• The high-pressure liquid refrigerant travels from the condenser, through the receiver-drier (if present), and then through the metering device before entering the evaporator inside the dash.


• After passing through the evaporator, the refrigerant becomes a low-pressure gas that returns to the compressor via the low-pressure suction line.

These details illustrate why the orifice tube is considered part of the high-pressure side and how it feeds the evaporator.

Orifice tube vs. expansion devices: key differences

The following overview contrasts common metering devices to clarify why placement matters and how they influence performance.

• Orifice tube: A fixed restriction that provides a constant metering flow. It is simple and cheap but does not adapt to changing cooling loads.


• Thermostatic expansion valve (TXV): A variable metering device that adjusts refrigerant flow to maintain evaporator temperature/pressure, offering better performance across different conditions but with higher cost and complexity.


• Impact on diagnostics: An orifice tube can become clogged, reducing cooling efficiency and altering pressures; TXVs can fail by sticking or leaking, affecting superheat control.

Understanding these differences helps technicians diagnose performance issues and plan service or replacement accordingly.

How to identify the metering device on your vehicle

Locating the device typically involves inspecting the metal tubing between the condenser/receiver-drier and the evaporator housing. An orifice tube is a short copper or aluminum tube with a fixed aperture, sometimes housed inside the receiver-drier assembly. When in doubt, consult the vehicle’s service manual or wiring diagram for the exact location by make, model, and year.

Summary

The orifice tube is not on the low side; it is situated on the high-pressure side of most automotive A/C systems, ahead of the evaporator. The low side begins after the evaporator and leads back to the compressor. While some designs place the metering device inside the receiver-drier, the fundamental principle holds: the metering element precedes the evaporator, not the low-pressure side. Awareness of this layout aids accurate diagnosis and effective maintenance of vehicle air conditioning.

Which side is the low side on an AC unit?

The low side of an AC system is the low-pressure side where refrigerant absorbs heat, primarily in the indoor or evaporator coil. This section includes the evaporator, the suction line, and the compressor inlet. It is the part of the system that operates at lower pressure and is responsible for the cooling effect you feel.
 
This video demonstrates how to add PAG oil to an air conditioning system using a vacuum, which involves working with the low side of the system: 55sLive FreeYouTube · Apr 18, 2024
How the low side works

• After passing through the expansion valve, the refrigerant is cold and low-pressure. 
• It flows into the evaporator coil, which is typically located inside the indoor unit of your AC. 
• The low-pressure, cold refrigerant absorbs heat from the warm air blown over it by the fan. 
• This absorption process turns the liquid refrigerant into a gas and cools the air, which is then circulated into your home. 
• The low side is also where the refrigerant gas is pulled back into the compressor to start the cycle again. 

Identifying the low side

• Location: The low-pressure service port is typically found on the larger diameter AC line between the compressor and the evaporator. 
• Connection: During a recharge or service, the blue hose on a manifold gauge set connects to the low side, while the red hose connects to the high side. 
• Temperature: When the AC is running, the low side lines and fittings will feel cold to the touch, while the high side will be hot. 

Do you add freon to high side or low side?

You charge an A/C system on the low side for most DIY applications because it is safer and recharge kits are designed for this port. The high side has extremely high pressure, and adding refrigerant there with a standard kit is dangerous and can cause a can to explode. The low-side port is where the compressor pulls in vapor, allowing it to be introduced into the system safely.
 
Why the low side is used for charging

• Safety: The low side has much lower pressure, making it safer to connect to. The high side's pressure is dangerously high when the system is running, and adding refrigerant can be explosive. 
• System operation: The low side is the suction side of the compressor. By adding refrigerant here, the compressor can safely draw in the vapor and mix it with the oil and the rest of the refrigerant. 
• Kit design: Recharge kits are designed to connect to the low-side service port. The fittings are different sizes to prevent accidental connection to the high side. 
• Proper charging: Recharge kits are specifically designed to connect to the low-pressure service port, and the fittings are different sizes to prevent accidental connection to the high side. 

How to charge on the low side

1. Locate the low-side port: It is typically a smaller fitting found on the line connecting the accumulator and compressor. It may be labeled with a "L" or have a blue or black cap. 
2. Connect the hose: Attach the recharge hose to the low-side port. Make sure it is securely connected. 
3. Follow the kit's instructions: Turn the vehicle on and set the A/C to its maximum setting. Shake the can as instructed by the kit before dispensing the refrigerant. 
4. Monitor the pressure: Use the gauge on the can to monitor the system pressure while adding refrigerant. 
5. Disconnect: Once the desired pressure is reached, disconnect the hose and recap the service port. 

Where is the orifice tube usually located?

An orifice tube is typically located inside the high-pressure A/C line (the smaller of the two lines) between the A/C condenser and the evaporator, often near the evaporator inlet. It can be found within the heater/A/C box, with its position secured by a crimp in the tube itself or a specific location near the radiator. To access it, you may need to disconnect the line and use a tool to pull the old tube out.
 
This video demonstrates the location of the orifice tube in a GM and Ford vehicle: 1mGreg's GarageYouTube · Sep 27, 2020

• Where it is: The orifice tube is a small component in the A/C system that controls refrigerant flow into the evaporator. It is situated in the smaller, high-pressure liquid line after the condenser. 
• How to find it: Look for the tube just before it enters the evaporator. It might be inside the heater/A/C box under the dashboard, or in the engine bay between the condenser and the evaporator. 
• How to identify it: The tube itself is often secured by a small crimp in the line, and the orifice tube is inserted into the line at that point. 
• Accessing it: To replace the orifice tube, you will first need to safely discharge the refrigerant from the A/C system. Then, the line must be disconnected to pull out the old orifice tube with a pick tool. 

You can watch this video to learn how to access and remove the orifice tube: 35sRogue WrenchingYouTube · Nov 18, 2022

Is the orifice tube on the high side or low side?

Some systems are designed so that the orifice tube is mounted in the high side of the liquid refrigerant line in the evaporator. In some systems, the orifice tube can be mounted in the condenser outlet, which can soften the hissing noises that traditionally are produced when this type of A/C system is turned off.