Thermo King 914970, Manual

Page: 122 / 186

Refrigeration Maintenance
122
4. Front seat discharge service valve, and
equalize the compressor to slightly positive.
Disassemble and inspect the discharge valve
plates.
Figure 48: Compound Gauge Indicating 20 in.
Vacuum
Three-Way Valve Condenser
Pressure Bypass Check Valve
The condenser pressure bypass check valve is
built into the three-way valve. This check valve
controls the bypass flow of refrigerant gas
between the condenser inlet line and 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 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 service gauge manifold set on
compressor.
4. Close (front seat) the receiver tank outlet
valve.
5. Operate the unit on Cool, and pump down the
low side to 0 in. (0 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 heat position
using relay board test. Low side gauge will
raise slightly. High side gauge will drop to
approximately 30 to 50 psig (207 to 345 kPa).
Gauges will equalize.
1. Check Valve
2. Heating/Defrost Position
3. Cooling Position
Figure 49: Three-way Valve Condenser Pressure
Bypass Check Valve