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Discussion Starter · #1 ·
On a heat pump with 3 service valves one that taps inside just above the accumulator, and two that connect to the lineset: a 3/8 smaller line, and 5/8 larger insulated line. Which lines are to be used for measuring subcool and superheat in both heating and cooling modes?
 

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On a heat pump with 3 service valves one that taps inside just above the accumulator, and two that connect to the lineset: a 3/8 smaller line, and 5/8 larger insulated line. Which lines are to be used for measuring subcool and superheat in both heating and cooling modes?
3/8 ( LiquidLine ) - subcooling
5/8 ( Suction Line)- SuperHeat
 

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The small line is always a liquid line unless the mfr puts a metering device before the service valve. The large line is superheated vapor only in cooling . For heating you'll use the other port.
 

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Discussion Starter · #5 ·
The small line is always a liquid line unless the mfr puts a metering device before the service valve. The large line is superheated vapor only in cooling . For heating you'll use the other port.
Thanks.

Just to verify - with regards to measuring subcool and superheat, when in:

  • Cooling mode use:
    • 3/8 (LiquidLine) - subcooling
    • 5/8 (Suction Line) - superHeat
  • Heating mode use:
    • 3/8 (LiquidLine) - subcooling
    • service port taps above accumulator (Suction Line) - superHeat

Is that correct?
 

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Correct. Not every heat pump has an accumulator but there will be a access port in the true suction line so you can get pressures.
 

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Discussion Starter · #7 ·
Correct. Not every heat pump has an accumulator but there will be a access port in the true suction line so you can get pressures.
Thanks.

Out of curiosity then, if not all have an accumulator, how do you prevent liquid flood-back during defrost?
 
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