How to Change an Expansion Valve

by Don Bowman

The expansion valve is attached to the side of the evaporator, which is in the heating and air conditioning (HVAC) case inside the vehicle. Its purpose is to transfer the refrigerant from the receiver-dryer to the evaporator at a low pressure. This change from a high-pressure refrigerant to a low-pressure super-cools the refrigerant converting much of it to a liquid. The cold gas and liquid mixture absorb the heat from the vehicle, which raises the temperature of the liquid and converts it back into a gas.


Connect the reclaimer to the high- and low-side valves on the air conditioning lines. Remove all the Freon. The high-side line is the smallest diameter line and has a red cap on the Schraeder valve. The low-side line is the larger of the two and has a blue cap on the Schraeder. Remove the caps and connect the reclaimer blue and red lines to the like-colored Schraeder valves.


Disconnect the high- and low-side lines from the evaporator inlet and outlet at the firewall, using a wrench. Remove any bolts that secure the evaporator case from the firewall side using the appropriate socket. Remove the glove box using the Phillips screwdriver. This makes it easier to gain access to the evaporator case.


Remove all electrical connectors on the evaporator case, followed by any vacuum lines or control cables.


Remove the screws in the case holding it to the heater core case, using a screwdriver. If the vehicle being worked on does not have room to remove the evaporator case, then the dash will need to be loosened so that it can be pulled rearward a couple inches to give the required room to remove the evaporator. This will require removing the side panels on the dash followed by removing the two or three bolts in the long dash support bar, using a socket. Remove any bolts that appear to be keeping the dash from moving rearward. In some cases, the center console may need to be repositioned to loosen the dash.


Pull the rubber drain tube out of the hole in the firewall. Pull the evaporator case out and down to remove it from the car. Remove the screws securing the two halves of the case together using a screwdriver. Lift the evaporator out of the case.


Pull the temperature-sensing bulb out of the evaporator core. Unthread the two pipe ends of the expansion valve and the single line from the valve to the bulb using a wrench.


Install the new valve in the same position as the old one and insert the new temperature-sensing bulb into the center of the evaporator core. Tighten all three line connectors to the valve. Install the evaporator back into the case from which it came. Join the two halves of the case, insert the screws and tighten.


Install the evaporator case in reverse order of removal. Install the remainder of the components in reverse order of removal.


Connect the reclaimer once more and this time draw the system into a vacuum for 15 minutes. If there are no leaks, the machine will vacuum the system down to 30 inches of mercury. Charge the air conditioning with the correct amount of Freon, which is stated on the hood or radiator cover.

Items you will need

About the Author

Don Bowman has been writing for various websites and several online magazines since 2008. He has owned an auto service facility since 1982 and has over 45 years of technical experience as a master ASE tech. Bowman has a business degree from Pennsylvania State University and was an officer in the U.S. Army (aircraft maintenance officer, pilot, six Air Medal awards, two tours Vietnam).

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