Hot Gas Bypass (HGBP)
designated by a C at end of model number
A
B
C
D
A. Liquid line to TXV
B. Hot gas line to HGBP is tee’d
into the hot gas line going to
the condenser.
C. Hot gas line from HGBP is tee’d
into liquid line downstream of TXV
D. Liquid line downstream of TXV
E. Low pressure tube attached to
suction line entering compressor
E
Sequence of Operation
The diaphragm in the HGBP
regulates the suction pressure
by opening and closing the valve
and allowing some of the hot gas that
would normally go into the condenser
to flow into the liquid line
downstream of the TXV.
As the suction pressure drops below
98 psi, (~31⁰ F) loss of pressure
from the suction line on the diaphragm (E)
will result in the HGBP valve opening
to allow hot gas to enter the liquid line
downstream of the TXV. This will
keep the suction pressure
up and the evaporator temperature
above the defrost point, allowing the
heat pump to operate in cooler
temperatures.
Trouble Shooting:
Symptoms of a failed hot gas bypass
1. Stuck open- abnormally high superheat (more than 15⁰ F), loss
of heating capacity
2. Stuck closed- heat pump defrosts more than normal, will not run at lower
temperatures (below 50⁰ F)
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