Refrigeration Maintenance
132
Three-Way Valve Condenser
Pressure Bypass Check Valve
A three-way valve condenser pressure bypass
check valve is used in this unit. This check valve
controls the bypass flow of refrigerant gas
between the condenser inlet line and the
compressor discharge line.
The check valve is closed when the unit is running
on cool, or whenever the discharge pressure is
higher than the condenser pressure.
When the unit is running on defrost or heat, if the
condenser pressure is higher than the discharge
pressure, the check valve opens and the condenser
pressure is bled off until it drops to the level of the
discharge pressure. The purpose of the valve is to
improve the three-way valve response time when
shifting from heat to cool.
If a three-way valve does not shift back to cool
immediately after the pilot solenoid closes, and
finally shifts to cool when the temperature rise
puts the unit into high speed, the three-way valve
end cap should be checked. See “End Cap
Checks” in the Refrigeration Service Operations
Chapter.
To check the operation of the condenser pressure
bypass check valve:
1. Remove the condenser pressure bypass check
valve cap from the three-way valve.
2. Using a screwdriver, gently turn the check
valve stem in until the valve is front seated.
3. Install a gauge manifold set on the
compressor.
4. Close (front seat) the receiver tank outlet
valve.
5. Operate the unit on cool and pump down the
low side to 20 in. Hg (-68 kPa) of vacuum.
6. Stop the unit. The condenser and suction
pressures should remain stable, indicating no
leaks.
7. Shift the three-way valve to the heat position.
The low side gauge will raise slightly. The
high side gauge will drop to approximately
zero. The gauges will equalize.
8. The gauges will remain in this position,
approximately zero, if the three-way valve
seals properly toward the condenser and the
condenser pressure bypass check valve seals
properly.
9. Back seat condenser pressure bypass check
valve stem against the snap ring. Both gauges
should rise indicating the condenser pressure
bypass check valve is properly releasing
condenser pressure into the discharge tube and
evaporator.
10. Replace the cap on the condenser pressure
bypass check valve.
NOTE: Valve stem MUST be back seated
during normal unit operation.
11. Open the receiver tank return outlet valve,
remove the gauges and return the unit to
normal operation.
1.
Check Valve
2.
Heating/Defrost Position
3.
Cooling Position
Figure 213: Three-way Valve Condenser
Pressure Bypass Check Valve
