ELECTRICAL
GENERAL (CONT.)
Single Point Connection (Medium Temp)
The “single point” connection system is designed to reduce the time required to install and wire one display case with one condensing
unit. Figure 31 on page 37 is a typical diagram for this system.
All of the display case controls, including the disconnect switch and electronic case controls, are installed behind the kickplate and
prewired. The liquid line solenoid valve is installed in the liquid line and wired.
The power to operate the display case is connected at the case disconnect switch. The power to operate the condensing unit is
connected in the condensing unit control panel. There are no interconnecting wires between the condensing unit and display case.
The controls operate the system as a pump down defrost. When the display case begins defrost, the liquid line solenoid valve is de-
energized. The fans and anti sweat heaters remain energized during defrost. The compressor continues to run and pumps down the coil.
The compressor cycles off on its low-pressure control. If there is any residual liquid left in the coil, the suction line pressure will rise and
the compressor may turn on and pump down the coil.
The liquid line solenoid is energized at the end of the defrost cycle. The suction line pressure rises and the compressor starts.
Master Satellite Connection (Low Temp)
The “master satellite” connection system allows one condensing unit to be connected to multiple cases. Figure 29 on page 35 shows
a typical diagram for this system.
All of the display case controls, including the disconnect switch, time clock, temperature control, and defrost temperature control, are
installed behind the kickplate and prewired. The liquid line solenoid is prewired but is not installed in the liquid line.
The power to operate each display case is connected at each case’s disconnect switch. The power to operate condensing unit is
connected at the condensing unit. There are no interconnecting wires between the condensing unit and display case. There are
interconnecting wires that need to be connected between the cases. The liquid line solenoid valve needs to be installed in the common
liquid line before the liquid is distributed to the cases.
The controls operate the system as a pump down defrost. When the display case begins defrost, the liquid line solenoid valve, fans and
anti-sweat heaters are de-energized. The defrost heaters are energized. The compressor continues to run and pumps down the coil.
The master case contains the time clock. Interconnecting case wiring allows the master case to control the satellite cases. When defrost
is initiated in the master case, it sends an electrical signal to each case to energize the defrost relay and initiate a defrost in all of the
satellite cases. A second set of interconnecting wires is connected in series between each of the cases. Each case defrost heater is de-
energized when the coil reaches the defrost termination temperature. An additional signal is relayed to the next case indicating that the
termination temperature has been reached. When all of the cases have reached termination temperature, the defrost termination circuit
is complete and the defrost is terminated.
The liquid line solenoid is energized at the end of the defrost cycle and the defrost heaters are de-energized. The suction line pressure
rises and the compressor starts. When the evaporator reaches operating temperature, the delay thermostat (klixons) will close, energizing
the fans and anti-sweat door heaters.
30 • Electrical - General
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