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Heat pump schematic (C) Carson Dunlop Associates

Reversing Valves on Heat Pumps
Definition, Location, Function, Repair

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Reversing valves:

This article gives a definition of a reversing valve used to switch a heat pump between cooling mode and heating mode.

We describe how a heat pump reversing valve works, how to find the reversing valve, and we include reversing valve troubleshooting advice and research articles. Page top sketch that includes a reversing valve is provided courtesy of Carson Dunlop Associates.



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Reversing Valves used on Heat Pumps

All Electric heat pump illustration Carson Dunlop Associates Different or Additional Controls for a Heat Pump vs an Air Conditioner

At HEAT PUMPS we introduced the different controls required to allow heat pump equipment to function in both heating and cooling modes and we explained how a heat pump works to provide both heating and cooling for a building. A heat pump is like an air conditioner, with a few control differences to allow the system to reverse the direction of heat movement between the indoor and outdoor areas.

When the heat pump is in cooling mode we are moving heat from inside of a building to the outdoors by blowing indoor air across a cooling coil, moving heat from the air into the coil and thus into the refrigerant in the coil. Outside that heat is ultimately expelled into the outdoor air.

[Click to enlarge any image]

When a heat pump is in heating mode the pump is moving heat from outdoor air into the building interior by moving outdoor air across the same outdoor coil that is now in heating mode. Depending on its efficiency, the outdoor compressor/condenser unit of a heat pump system can extract heat from outdoor air even down to temperatures below freezing.

In an air conditioner-only system, the outdoor coil is used only to cool and condense high temperature high pressure refrigerant gas back to a liquid refrigerant, and the indoor coil is used only to expand the liquid refrigerant to a gas (through an expansion device such as a Thermostatic Expansion Valve (TEV) or a capillary tube (Cap Tube).

Because a heat pump has to be able to work in both directions, its indoor and outdoor coil have to be able to exchange roles. To accomplish this the heat pump will need two refrigerant metering and expansion devices, one at each coil. Only one of the expansion devices is operating at a given time - depending on whether the equipment is operating in a heating or in a cooling mode.

Illustrations of expansion devices and reversing valve operation on a heat pump were provided by Carson Dunlop Associates, a Toronto home inspection, report writing & education company.

Reversing Valve and Defrost Cycle Operation Procedure for Heat Pumps

All Electric heat pump illustration (C) Carson Dunlop Associates

In addition to the two expansion devices, the system may make use of a reversing valve that changes the direction of flow of refrigerant gas and liquid in the system.

An additional set of controls for operation the refrigerant reversing valve and the operation of the defrost cycle for a heat pump are illustrated at left. During a defrost cycle

  1. The reversing valve changes direction of the refrigerant flow to send warmed refrigerant "freon" to the outdoor coil in order to melt ice that may have formed there.
  2. During the defrost cycle the outdoor fan stops - we want to stop moving outdoor air across the outdoor coil in order to allow the warm refrigerant to warm the coil.
  3. If the system includes electric heating elements, one stage of the electric BACKUP HEAT for HEAT PUMPS may be activated in the blower compartment to warm air coming off of the blower.

    If the heat pump system does not include electric backup heaters, the indoor air handler blower will stop during the defrost cycle so that we don't' blow wrong-temperature air into the occupied space.

Below: a photograph of a thermostatic expansion valve or TEV used on a heat pump system.

The thermostatic expansion valve or TEV (or TXV) shown in the photo is used on a heat pump system so it includes extra tubing so that as we will explain here, with the heat pump's reversing valve the TEV can permit the refrigerant to reverse its flow of direction when changing from cooling mode (move indoor heat to outdoors) to heating mode (collect and move outdoor heat to indoors).

TEV valve (C) D Friedman

Simple Tests Diagnose Heat Pump Reversing Valve Problems

To detect a defective reversing valve the HVAC service technician will simply measure the temperature on each of four lines going to and from the reversing valve.

She will observe the following if the reversing valve and heat pump system is working normally:

In Heating Mode

In Cooling Mode

Note: the reversing valve might be actuated to switch between heating and cooling mode in two ways:

  1. A room thermostat includes a switch from HEAT to COOL, typically using a wire connected to the "O" (orange wire) terminal that operates the reversing valve
  2. A control circuit board in the heat pump may operate the reverse valve in order to provide a defrost cycle for the system

Where is the Physical Reversing Valve Located?

Goodman Amana reversing valve sold by various online and local HVACR retailers and suppliers - at InspectApedia.comThe reversing valve will normally be found built into the heat pump compressor/condenser unit and soldered to refrigerant pipes or lines like those shown in this photograph adapted from a Goodman / Amana reversing valve

We added numbers to point out the four refrigerant connection ports on the valve. You can see the actuator coil assembly on the right side of the valve along with its connecting wires to connect the valve to the heat pump's control board.

Question: repair a capillary tube with epoxy?

(May 13, 2014) Ron said:

Can leaking capillary tubing entering solenoid body of the reversing valve in a R-22 system be repaired with epoxy.

Reply:

Ron,

Interesting question. I'm doubtful that a leaky cap tube can be reliably repaired, in part because I figure that you'll get epoxy in the small orifice of the tube interior and foul up its metering rate. Hell, it's worth a try anyway as if you ruin it you needed a new one anyway. Clean the surface, dry it, and try a patch.

Reversing Valve Specifications, Sources, Research

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Continue reading at THERMOSTATIC EXPANSION VALVES, REFRIGERANT or select a topic from the More Reading links or topic ARTICLE INDEX shown below.

Or see CONTROLS & SWITCHES, A/C - HEAT PUMP

Or see these

Articles on Heat Pumps

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REVERSING VALVE on HEAT PUMPS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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