Thermo King 914 724, Manual

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Refrigeration Maintenance (Rev. 1/99)
50
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 con-
denser pressure.
When the unit is running in defrost, if the condenser pres-
sure 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 check
valve is to improve the heating/defrosting ability and the
three-way valve response.
To check the operation of the 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 in cool and pump down the low side to
20 in. Hg of vacuum (-68 kPa).
6. Stop the unit. The condenser and suction pressures
should remain stable, indicating no leaks.
7. Shift the three-way valve to the defrost position. The
low side gauge will rise slightly and the high side gauge
will drop to approximately zero as the gauges will
equalize.
8. The gauges will remain in this position (approximately
zero) if the three-way seals properly toward the con-
denser and the condenser pressure bypass check valve
seals properly.
9. Back seat the condenser pressure bypass check valve
stem against the snap ring. Both gauges should rise
indicating that 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: The check 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 operation.
1. Check Valve
2. Cool Position
3. Defrost Position
Three-way Valve Condenser Pressure
Bypass Check Valve