Thermo King SB-190 30, Manual

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Refrigeration Maintenance (Rev. 12/03)
61
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 heating/defrosting ability and three-
way valve response.
To check the operation of the 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. Low side
gauge will raise slightly. High side gauge will drop to
approximately zero. Gauges will equalize.
8. Gauges will remain in this position approximately zero
if the three-way valve seals properly toward the con-
denser and the condenser pressure bypass check valve
seals properly.
9. Back seat condenser pressure bypass check valve stem
against 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 nor-
mal 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
Three-way Valve Condenser Pressure
Bypass Check Valve