74 TGZ 040A through TGZ 190A OMM TGZ-1
Optional Controls
Part Winding Start
Part winding start is available on all voltage units and consists of a solid-state time delay
wired in series with the contactor that energizes the second winding of each compressor
motor. Its purpose is to limit current inrush to the compressors upon start-up. As each
compressor starts, the contactor of the first motor winding is delayed for 1 second.
Control checkout is best accomplished by observation as each contactor is pulled in to see
that the 1 second delay occurs before the second contactor pulls in.
Figure 10, Part Winding Start Option
Note: Line is only hot when the unit calls for compressor to run.
Phase/Voltage Monitor (Optional)
The phase/voltage monitor is a device that provides protection against three-phase electrical
motor loss due to power failure conditions, phase loss, and phase reversal. Whenever any of
these conditions occur, an output relay is deactivated, disconnecting power to the
thermostatic control circuit. The compressor will automatically pump down.
The output relay remains deactivated until power line conditions return to an acceptable
level. Trip and reset delays have been provided to prevent nuisance tripping due to rapid
power fluctuations.
When three-phase power has been applied, the output relay should close and the “run light”
should come on. If the output relay does not close, perform the following tests.
1. Check the voltages between L1-L2, L1-L3, and L2-L3. These voltages should be
approximately equal and within +10% of the rated three-phase line-to-line voltage.
2. If these voltages are extremely low or widely unbalanced, check the power system to
determine the cause of the problem.
3. If the voltages are good, turn off the power and interchange any two of the supply
power leads at the disconnect.
This can be necessary as the phase/voltage monitor is sensitive to phase reversal. Turn on
the power. The output relay should now close after the appropriate delay.
Hot Gas Bypass (Optional)
This option allows passage of discharge gas to the evaporator permitting operation at lower
loads than available with compressor unloading. It also keeps the velocity of refrigerant gas
high enough for proper oil return at light load conditions. A solenoid valve in the hot gas
bypass line is wired in parallel with the compressor unloader U1. Thus, the hot gas solenoid
cannot open unless the compressor is operating in an unloaded mode. If only one hot gas
valve is specified for the unit, the hot gas bypass is wired in the first refrigerant circuit and
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