Heat Pump Reversing Valve 101

The reversing vale is one of the main components on a heat pump that makes it function by being able to reverse the direction of refrigerant.

<>    Image of a heat pump reversing valve out of the box with no solenoid coil. (click on the image to see the larger view). The picture of this valve was taken before being installed on a 20 year old Dunham Bush unit that the previous valve was damaged due to improper installation. This, and most reversing valves are made by Ranco but could also have been made by Alco (division of Emerson Electric).

    This valve does not have the electric coil installed which would be where the silver frame is. Once the valve is installed and the system tested for leaks the coil will be added. The valves come in different configurations to accommodate piping angles and system capacities (to be added later).

    Replacing one of these valves is not a job for the faint of heart. It is one of the most difficult repair that you can make on a heat pump above and beyond replacing the compressor. Installing the valve is difficult enough, not burning it up is even harder. It requires very good brazing skills and media to cool the valve while brazing. On one job we used snow to cool the valve between joints.

    There is a right and wrong direction to install the valve. On most system the valve is installed so that with no power to the valve it will be in heating mode, Rheem, Ruud, and Weatherking (don't ask me why) the valve is placed so that cooling is the default even if it has a relay to invert the 24 volt AC "O" signal. On Rheem and Ruud they may also use a line voltage coil as opposed to 24 volts from the inside, so if the unit is in heating when unit power is removed it will revert to cooling instantly, this could be a real surprise when servicing. On other systems there is no such thing as the reversing valve "reverting to cooling" or "going into heating mode" It will only go into cooling with a signal to the coil otherwise it is in the heating mode.

    The way the reversing valve works is the solenoid valve controls the high and low pressure ports in the center of the valve to operate a nylon slider in the cylinder by diverting high and low pressure to the end of the cylinder.

    Reversing valves are relatively trouble free and in my career I have replaced about 5. The main problem is the sleeve can jam or bind half way (called "wind milling") and will over heat the compressor in a few minutes. Once this happens there is little chance that the valve will work again. If the valve is over heated when being installed it is trash and will never move. If the system is very contaminated after a "Compressor Burn Out" it may stop the valve form working but there is the possibility of getting it to work again after several cycles. It is possible for the valve to stick in the cooling mode but it is more likely to stick in the heat mode.

(remove) To do the job replacing this valve we charged $800 (1999) and that included adding a TEV for the heat mode to replace a capillary and adding a start kit. The unit that this went into is in excellent shape and has a suction to liquid heat exchanger to increase efficiency. This heat pump is used with an oil furnace.