Heat Pump Reversing Valve 101

    I get many question about and I make reference to the reversing valve on heat pumps. Until now I have no pages on it but That is changed. Here it is.

Image of Heat Pump Reversing valve.

    Image of a heat pump reversing valve out of the box (click on the image to see the larger view). This valve is about to be installed on a 20 year old Dunham Bush unit that the previous valve was damaged due to improper installation. This valve is 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.

    Replacing one of these valves is not a job for the faint of heart. It is 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 way to install the valve. On most system the valve is installed so that with no power to the valve it will be in heat mode, Rheem and Ruud (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 also use a high 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. Which means that 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 opens pressure ports to operate a nylon slider in the cylinder. This 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 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.

    To do the job replacing this valve we charged $800 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.

    This page will be updated soon

 Good Luck Scott
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Written By:  Scott Meenen N3SJH of:
Specializing in Mechanical, Controls and Electrical Modifications Of
Heating, Air-conditioning, Refrigeration, Cold storage,
Ice Production and Food preservation.
Anything having to do with Heat and Energy.
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                 This text written by: Scott Meenen * G & S Mechanical

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