1) At the thermostat, remove the wire at the O/B terminal. The reason for this is a key component called the reversing valve. So you should be able to check the wiring at the air handler. The determination for mode of operation is the presence or absence of an “O” signal from the stat. Refrigerant is the chemical mixture that allows for the heat exchange to occur. Professionals can sometimes repair the reversing valve, put will often need to replace it. Video of a confirmed diagnosis of a 3-way reversing valve not cooling but heating ok. It will operate and blow heat like I've died and gone to hell, but it won't go the other direction and cool. An electrical connection from the thermostat controls whether the reversing valve is energized or de-energized. The reversing valve is energized for cool mode, de energized during heat pump mode operation. The heat pump can be designed by the manufacturer to produce either cooling or heating with the reversing valve in the relaxed state. In Figures 2 and 3, the pilot valve has been configured so that when the pilot valve is de-energized, the system is in the heating mode, and energizing the pilot valve the system is in cooling mode. not all reversing valves energize in heating most do not. The reversing valve has two states, relaxed (unactivated) versus energized. Its easy to find out. Now let's complicate it a bit more.....While not in the majority, there are some units out there that instead of energizing the reversing valve in cool mode, they work in reverse and require that you energize the reversing valve in heat mode, typically using the B terminal and blue wire. If it was -20 outside, and your reversing valve failed, you will still have heat, you can survive (don't tell that to my customers) without a/c but you will die without heat in reality. The main difference is that a heat pump can both heat and cool a home, whereas an air conditioner just cools a home. I have found that the reversing valve is energized on the cooling cycle, but also even if thermostat is set to off position valve is still energized. (Tapping on the valve, making sure there was power to the valve, made sure that I was using the B terminal instead of the O terminal, etc.) The reversing valve. heat so I could measure the voltage at the reversing valve and got 24 volts. there should also be a setting in the menu telling it whether to energize reversing valve on heating or cooling. Heat pumps and heat/cool units: many original equipment manufacturers connect the system tubing to the Ranco reversing valve based on which mode (heat or cool) the system will operate, should the solenoid coil fail. Start studying Reversing Valve 4 Way- Valve Heat Pumps. 4-Way Reversing Valve with operating control used for heat pumps. The selenoid energized.The other unit wired the same way working fine. I just installed a new Ruud heat pumps a couple of weeks ago. Voltages is ~24v ac. The energized state is typically achieved by applying 240 volts AC, which is commonly used in HVAC equipment. It allows the heat pump to operate in either the heating. im considering buying a armstrong heat pump to add to my existing gas only furnace to make it dual fuel. In a heat pump, a reversing valve controls the direction of the flow of refrigerant. The blue on the reversing valve should be common or C and the orange should go to the O terminal of the thermostat. Shown here, the heat pump cooling works like any cooling system when it is in cooling mode. Typical wiring diagram for heat pump with reversing valve energized in COOL TRANSFORMER Reversing Valve* B O RC JUMPER WIRE Compressor Contactor JUMPER WIRE * Reversing valve is energized when the system switch is in the COOL position Fan Relay Y RH 24 VAC 120 VAC Hot Neutral THERMOSTAT SYSTEM G W Figure 7. The reversing valve has two states, relaxed (unactivated) versus energized. The solenoid does not actually shift the main valve, it only shifts a much smaller pilot valve that then uses system pressure to shift the valve. But when calling for normal heat, it goes into the cooling cycle. The reversing valve is energized when there is a call for heat Also, with the thermostat in "system off", no voltages except on the R and RH terminals. Refrigerant: The substance in the refrigeration lines that circulates through the indoor and outdoor unit. Either your system uses O or B, not both. Bad reversing valve – If you have a heat pump not heating, but it works in cooling mode, you might have a bad reversing valve. On my newer CrapAir unit, it appears the reversing valve is stuck. Some units use energized reversing valve during cool and some de-energized. This reversing valve solenoid, partially controlled by the HP thermostat, is generally energized in the cooling mode (except as noted above). When looking at a reversing valve, the single port on the bottom is always the discharge line from the compressor. I tried everything. A heat pump has a few extra parts that allow it to reverse the direction of heat exchange. If the reversing valve is energized during this test, ... the suction gases can absorb heat from the wayward hot gas bleeding across the valve diminishing the amount of sensible heat rise across the valve. Basically before heat pumps refrigerant flowed one direction. Reversing Valve Position Selects “O” or “B” Setting For Heat Pumps Only O O B 2 Fn Circulating Fan OFF Off/10% – 100% (5% increments) I have 2 units (0ne works well)and it appears that the switching valve is not operating. REVERSING VALVE ENERGIZED IN COOL MODE ONLY REQUIRED FOR HEAT PUMPAPPLICAITON REVERSING VALVE ENERGIZED IN HEAT MODE Basic Installation Single Stage Thermostats 1E78-144 Non-Programmable 1E78-151 Programmable For additional information visit: www.white-rodgers.com With the reversing valve de-energized the flow reverses. Please check your heating and cooling system manual or consult a professional HVAC technician if you do not know which option to select. A refrigerant reversing valve with an electromechanical solenoid coil is used to reverse refrigerant flow during unit operation (see Figure 10-14). If I cut breaker of to unit you can hear valve coil click as it is de-energizing, or if you put unit in heating cycle you can hear valve click as it is de-energizing. 0 = cooling reversing valve, energized in cooling mode. If the valve breaks, the heat pump will be trapped in one mode or the other. However, there are instances where the reversing valve is off when running cool mode. B on the stat is reversing valve energized in heating mode. This determines whether you are going to heat or going to cool. Condensing unit runs, but just won't push the gas back the other way. selenoid the reversing valve goes into heat. Initialization Reversing valves: Change the flow of refrigerant which determines if your interior space is cooled or heated. Welcome to the forums. Cool Low Pressure Gas. This will energize the reversing valve to go into cooling. lennox energize in cooling for instance. 99% of heat pumps I have seen are energized for cooling and are designed to fail heat. A reversing valve is usually found close to the compressor or condenser of the heat pump. Reversing valves can easily be configured for opposite operation. A broken reversing valve will mean a heat pump that is trapped in one mode or the other. ... My Coleman 3700 THE 2.5 ton heat pump /ac will not switch to the cool mode. When the reversing valve is called upon to shift from the "down" position, the pilot solenoid valve is energized, closing its compressor discharge pressure port and connecting the chamber on top of the piston to the compressor suction line. This is a job for your local Carrier expert. If the Reversing Valve is energized on a call for heating, what Terminal on the Sub-Base must be used? Figure 6. This valve is specialized for heat pumps, and when issues arise with the reversing valve in your heat pump, there will be operational issues. The reversing valve solenoid is an electromagnetic coil that mounts onto the reversing valve and is generally 24V on residential heat pumps. Because many heat pumps can lose efficiency as outdoor temperatures fall below freezing, your system probably has a supplemental heat source – either electric resistance heating elements, or a gas or oil furnace. or cooling mode by changing the direction of the refrigerant between the indoor and outdoor coils. In most cases, the reversing valve is energized when running cool mode. The energized state is typically achieved by applying 24 volts AC, which is commonly used in HVAC equipment. The heat pump can be designed by the manufacturer to produce either cooling or heating with the reversing valve … Wire it in and set the reversing valve to stay on cool cycle and never reverse to heat and viola. This is called the 4-Way Reversing Valve, because it has four connections refrigerant pipes.Because the heat pump uses of reversible mechanical refrigeration cycle, such device is not required. It works fine in cooling. Coils: The condenser and evaporating coil heat or cool the air depending on the directional flow of refrigerant. Works fine in emergency heat. Therefore, it is important the check the manufacturer's specifications of the heat pump system that you are using before you can do a proper connection to the thermostat. i have got a chance to get a great deal on a armstrong a-coil and heat pump. In a heat pump system when the reversing valve is energized (cool mode), the unit will run in cool mode and the refrigerant will follow the path indicated on the bottom. HEAT PUMP SYSTEM: Configure the reversing valve for O (energized in cool) or B (energized in heat) and enable/ disable Emergency Heat and/or Auxiliary Heat. It needs another expansion valve, and it needs a reversing valve. I intentionally turned the Tstat up high enough to turn on the aux. Slap a reversing valve on there and when it calls for heat the reversing valve gets energized and the flow is backwards. When the heat pump switches between its heating and cooling modes, it’s the change in the reversing valve that makes it happen. 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