If your air conditioning (AC) has been less than helpful this summer, it may be the expansion valve (also known as an orifice tube). AC expansion valves regulate the flow of refrigerant through the AC system and if the valves fails they can cause problems with the whole system. Diagnosing your car’s air conditioning system may reveal that your expansion valve or the orifice tube needs to be replaced.
Replacing an expansion valve requires special equipment and there are a number of laws regarding handling refrigerants. So it is strongly recommended that you engage a professional to do this job. But if you want to tackle this job yourself, there may be ways to get help with the heavy equipment.
Part 1 of 4: Evacuating the system
Materials Needed
- AC manifold gauge set
- Refrigerant identifier
- Refrigerant recovery system
- Safety glasses
- Workshop manual
Step 1: Identify the refrigerant. Using the service manual, locate the low pressure fitting of the two AC service fittings on the car and connect the refrigerant identifier to the car. The refrigerant identifier will take a small sample of the refrigerant in the system and tell you if it is recoverable or not.
This is important for two reasons:
One, because recovering contaminated refrigerant will not only damage the equipment, it will spread the damage like a virus to every car that is later hooked up to that equipment.
Two, there have been some unscrupulous workshops who, in order to save money on refrigerant, have been filling AC systems with butane which causes an explosion hazard.
The refrigerant identifier will indicate what type refrigerant your car has and whether the refrigerant is clean enough to recover. Cars made in the 1980s may still use R12 refrigerant, while cars made since 1990 will use R135 A refrigerant. The refrigerant must be recovered by the appropriate equipment. If you find out the refrigerant is contaminated, in can only be withdrawn from the system into a specialized storage container for disposal.
Step 2 Recover the refrigerant. You can connect the recovery system directly to the car, or connect it via the manifold gauges. Refrigerant is recovered using the low pressure port on the system.
Open the valve on the storage tank, turn on the switch and let the machine chug away until it sounds an alarm. This might take as much as 20 minutes if the system is full. If you can’t get access to the appropriate recovery machine by borrowing or renting, you can have a mechanic come to your house and evacuate the system for you.
Part 2 of 4: Replacing the expansion valve
Materials Needed
- Allen wrenches
- New expansion valve
- O-rings
- Refrigerant oil
- Safety glasses
- Screwdrivers, both blade and phillips
- Socket wrench set (1/4 drive)
- Wrenches, open ended
- Workshop manual
Step 1: Locate the expansion valve. It’s best to buy your expansion valve and O-rings before you begin because the air conditioning system should not be “open” for any longer than necessary. If you can’t complete the job all at once, you should plug any disconnected lines to keep atmospheric moisture from entering the system.
Use your workshop manual to determine whether your car uses an expansion valve and where it is located. Cars that don’t have an expansion valve will use an Orifice tube which is covered in a later section.
If you are lucky, the expansion valve will be located somewhere under the hood, under the cowl or near the firewall. If you aren’t, it may be located under the dashboard and you’ll get to spend the next couple of hours working while laying upside down in a very tight space.
Some cars will require removing the heat-exchanger box from the car in order to access the part. If you have trouble finding the expansion valve, follow the high pressure line from the receiver-dryer toward the firewall, it may disappear into a trim panel or a cowl panel which you will have to remove.
If you don’t find the expansion valve under the panel, you’ll have to remove the panels under the dashboard and look for it on the other side.
Step 2: Remove the expansion valve. The expansion valve will have at least two refrigerant lines going to it and may have a fine capillary tube as well. Some models have four lines that are held on by fastening plates.
There may also be a capillary tube with a flare nut connecting to one of the larger lines, or it may be inserted into the evaporator core, where it can sense the evaporator temperature. It should be possible to simply pull the tube out of the evaporator through the hole in the evaporator case.
Step 3: Replace the O-rings. Whenever an air conditioning line is disconnected, the O rings should be replaced with new ones.
O-rings should be soaked in the appropriate refrigerant oil before use. Just put some oil in a small dish and throw all your O-rings in it before you start disconnecting the valve, and they will be ready for use by the time you need them. Slip them carefully onto the disconnected lines.
Step 4 Reconnect the expansion valve. Carefully re-connect the lines to the expansion valve and install the fasteners. It’s easy to get them on crooked, so if they do not thread on easily, check and be sure that the connections are straight. Gently push the capillary tube back into the evaporator case through the hole where it came out. It should be a straight shot.
Part 3 of 4: Replace an orifice tube
If your system uses an orifice tube instead of an expansion valve, most of the procedures are nearly the same, the difference is that the orifice tube is located Inside the line going to the evaporator.
Materials Needed
- Orifice tube
- Orifice tube extractor tool
- O-rings
- Needle-nosed pliers
- Refrigerant oil
- Workshop manual
- Wrenches, open ended
Step 1: Locate the orifice tube. The orifice tube will be inside the high-pressure line to the evaporator. Most orifice tube systems have the evaporator under the hood or cowl, Find where the line steps up in size just before a joint. The orifice tube should be in there.
Step 2: Open the line. Once you break the connection, you should see a plastic tab inside the line. It may be possible to just pull it out with the needle nosed pliers, but if it doesn’t want to move easily, you need to use the orifice tube extraction tool. The extraction tool can be inserted into the pipe, and by turning it will engage tabs on the orifice tube that are present to enable removal.
Notice if the screen is damaged or clogged with debris. If so, there may be damage elsewhere in the system.
Smear some refrigerant oil on the o rings and insert the new orifice tube into the line. Observe the direction, it’s easy to put it in backwards. The new orifice tube should have an arrow on it that should go in pointing toward the evaporator. Put new O rings on the line and re-connect the line.
Part 4 of 4: Recharging the AC system
Recharging the AC system is a procedure best left to trained personnel. It requires specialized equipment and the performance of the system can vary widely depending on weather it is done correctly. Installing exactly the right amount of refrigerant and oil is critical which can only be done with the proper equipment. Additionally, in some states you have to be a certified technician in order to buy refrigerant.
For those reasons, it is strongly recommended that you have a professional recharge the system. If you want to try it yourself, follow this procedure for recharging the car’s air conditioning system.
If you decide you don’t want to spend a hot summer day working under your hood or upside down under the dashboard, or you just want to have help with the evacuation and recharge of the system, contact a trained mechanic with all the necessary equipment.
