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Old 06-18-2010, 10:11 AM   #1
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Txv therory of operation


I'm trying to understand how a TXV works on a heat pump in both directions..

In heating mode High Pressure, High temperature vapor is going through the suction line to the indoor coil. The high temperature is on the bulb and the pressure sensor. And that is used to meter the flow out of the indoor coil.










In cooling mode Low Pressure, Low temperature vapor is going through the suction line out of the indoor coil. The low temperature and Low pressure is on the suction line and that is used to meter the flow into the indoor coil.





I can't seem to find any similar diagrams of a TXV valve that actually has a bulb and a connection to the larger "suction" line pressure sense connection. This pic appears to be a one-way TXV valve. Are the modern ones really two way and work in both directions? Or do they bypass in one direction.




Can someone explain how the TXV on my heatpump is able to work in both directions?

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Old 06-18-2010, 10:35 AM   #2
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Txv therory of operation


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Originally Posted by zootjeff View Post
Are the modern ones really two way and work in both directions? Or do they bypass in one direction.
In a heat pump application they bypass in the reverse direction. Either by using an internal or external check valve.

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Old 06-18-2010, 10:37 AM   #3
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Txv therory of operation


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Originally Posted by hennyh View Post
In a heat pump application they bypass in the reverse direction. Either by using an internal or external check valve.
Then why are they required on a heat-pump to get the higher efficiency rating and why do they have two capillary connections instead of the one showed in the diagram I posted?
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Old 06-18-2010, 01:35 PM   #4
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Txv therory of operation


The TXV at the indoor coil. Only meters refrigerant in cooling mode. It is internally bypassed in heating mode.
Your outdoor unit has its own metering device for heating mode.

The Indoor TXV is only needed to get the higher SEER rating. Which is a cooling rating.

If by 2 capillaries. Your referring to the line that goes from the TXV body, to the vapor line. That is an external equalizer.
The Capillary at the top of the TXV is for the power head and sensing bulb. And has no opening into the TXV its self.
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