Automotive AC Repairing and Replacing – Replacing the Standard-Style Thermal Expansion Valve

The thermal expansion valve is a metering device that can have two different designs. The standard type is usually located inside the duct box and requires major effort and steps to replace. The block-type valve is usually located somewhere near the firewall and is much easier to replace when needed. See chapter 3 for more details about the operation of this component. Below are the steps to follow when replacing the standard-style thermal expansion valve.

1. After recovering the refrigerant or verifying that the AC system is empty, follow the procedures to remove the duct box from the vehicle. This is a very labor-intensive procedure that should only be done by someone with a strong mechanical ability and a complete set of technician’s tools.
2. Remove the top/cover of the HVAC duct box to gain access to the evaporator core and thermal expansion valve.
3. Remove the insulating tape from the thermal element.

The thermal expansion valve capillary tube needs to be removed from the exit line of the evaporator core. This part of the valve is insulated with sticky insulating tape that must be removed during the

4. Use the correct wrenches to unbolt the thermal expansion valve from the evaporator core plumbing. The final steps of removing the fasteners can be done by hand.

The thermal expansion valve must be disconnected by removing the hex fasteners. The O-ring needs to be replaced before the new valve is installed. The fitting needs to be torqued to the correct tightness during installation to ensure a quality

5. Install the correct O-rings or seals to the new thermal expansion valve. Refrigerant oil should be added to the O-rings, but any metal gaskets should be installed dry.

The new thermal expansion valve should be inspected to make sure it is the correct model for the vehicle being

6. Install the thermal expansion valve into the correct position. Close attention needs to be paid when installing the temperature-sensing bulb onto the evaporator exit line. The fasteners need to be tightened to the correct torque using a torque wrench.

After torquing the fasteners for the thermal expansion valve, the sticky
insulating tape needs to be applied around the capillary tube area to
ensure that the tube firmly touches the evaporator exit

7. Reassemble the duct box, paying close attention to the position of each duct door being in a normal location of travel. If the box is assembled with one of the doors outside the normal area of travel, then the box will have to be opened back up to correct this problem.
8. Reinstall the duct box back into the vehicle, paying close attention to assembling all fasteners back into their original location.
9. The AC system can be evacuated and recharged before being returned to service.

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