IM 986-2 / Page 45 of 48
Figure 62: Cooling Mode
Return Air
Reversing Valve
Conditioned Air
(Cooling)
Thermal
Expansion Valve
Coaxial Heat
Exchanger
Blower
Coil –
Air to
Refrigerant
Heat
Exchanger
Water In
Water Out
Sensing Bulb
and
Capillary Tube
Compressor
Figure 63: Heating Mode
Return Air
Thermal
Expansion Valve
Coaxial Heat
Exchanger
Reversing Valve
Conditioned Air
(Heating)
Blower
Water In
Water Out
Sensing Bulb
and
Capillary Tube
Compressor
Coil –
Air to
Refrigerant
Heat
Exchanger
Troubleshooting Refrigeration Circuit
Cooling Refrigeration Cycle
When the wall thermostat is calling for COOLING, the
reversing valve directs the flow of the refrigerant, a hot gas,
leaving the compressor, to the water-to-refrigerant heat
exchanger. Here the heat is removed by the water and the
hot gas condenses to become a liquid. The liquid then flows
through a thermal expansion metering system to the air-to-
refrigerant heat exchanger coil. The liquid then evaporates
becoming a gas, at the same time absorbing heat and cool-
ing the air passing over the surfaces of the coil. The refriger-
ant then flows as a low pressure gas through the reversing
valve and back to the suction side of the compressor to
complete the cycle.
Heating Refrigeration Cycle
When the wall thermostat is calling for HEATING, the revers-
ing valve directs the flow of the refrigerant, a hot gas, leaving
the compressor, to the air-to-refrigerant heat exchanger coil.
Here the heat is removed by the air passing over the surfac-
es of the coil and the hot gas condenses to become a liquid.
The liquid then flows through a capillary thermal expansion
metering system to the water-to-refrigerant heat exchanger.
The liquid then evaporates becoming a gas, at the same time
absorbing heat and cooling the water. The refrigerant then
flows as a low pressure gas through the reversing valve and
back to the suction side of the compressor to complete the
cycle.
Charge
Undercharge System Low Low Low High Low Low Low Low Pressure
(Possible Leak)
Overcharge System High High High Normal High Normal High Pressure
Low Air Flow Heating
High High High
Low High Low High Pressure
Low Air Flow Cooling
Low Low Low
High High Low Low Temp
Low Water Flow Heating
Low Low High Low High Low Temp
Low Water Flow Cooling High High High High Low Low High High Pressure
High Air Flow Heating
Low Low Low Low High Low Low Low Temp
High Air Flow Cooling
Low High Normal High Low Low Normal High Pressure
High Water Flow Heating
Normal Low Normal High Normal Normal Low High Pressure
High Water Flow Cooling
Low Low Low Low High Normal Low Low Temp
TXV Restricted High Low High High Low Low
Low
Normal
Normal
Low
High
Normal
Low
Normal
Low
Normal
Normal
Low
Air Water Safety
Head Suction Compressor
Super
Temp (loops) Temp Lock
Symptom
Pressure Pressure Amp Draw
Heat
Subcooling
Differential Differential Out
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