System
a.Could cause serious compressor damage due to refrigerant floodback.
b.Removes working surface from the evaporator normally used for heat transfer. Systems operating with superheat in excess of 16 degrees:
c.Could cause excessive compressor cycling on internal winding thermostat which leads to compressor motor failure.
d.Lowers the efficiency of the evaporator by reducing the heat transfer capability.
The outdoor ambient temperature must be between 65ºF and 105ºF and the relative humidity of the air entering the evaporator must be above 40 percent. When the temperatures are outside of these ranges, measuring the operating pressures can be meaningless.
Figure 42. W7100G Staging Sequence
Condenser Fans
Condenser fan cycling is accomplished through interlocking the fan contactors with liquid line pressure switches (4S11 and 4S12). When the low ambient damper option is applied, ambient thermostats (1S36 & 1S37) are used to provide additional fan cycling control on “No System Control”, Constant Volume, and Variable Air Volume applications. Figure 43 illustrates the condenser fan locations with their respective fan and relay designator.
When a cooling command has been initiated (circuit #1, first step), condenser fans 2B1, 2B2, and 2B3 are held “Off” by the liquid line pressure switch (4S11) and normally open interlock contacts 1K5 & 1K6. Once the pressure switch has closed (275 psig), condenser fan relay 1K5 is energized starting fan 2B1. The normally open interlock contacts 1K5 closes, energizing fan contactor 1K6, starting fan 2B2. When the normally open interlock contacts 1K6 close, they seal 1K6 contactor in the “On” position until the cooling demand has been satisfied. Condenser fan 2B3 on 25, 30, 50 & 60 Ton units is not allowed to start until compressor relay 1K13 has energized and the low ambient thermostat (1S36, if applicable) has closed.
If a second step cooling command is initiated, (circuit #2), condenser fans 2B4, 2B5, and 2B6 are held “Off” by the liquid line pressure switch (4S12) and normally open interlock contacts 1K8 & 1K9. Once the pressure switch has closed (275 psig), condenser fan relay 1K8 is energized starting fan 2B4. The normally open interlock contacts 1K8 closes, energizing fan contactor 1K9, starting fan
2B5. When the normally open interlock contacts 1K9 close, they seal 1K9 contactor in the “On” position until the cooling demand has been satisfied. Condenser fan 2B6 on 50 and 60 Ton units is not allowed to start until compressor relay 1K14 has energized and the low ambient thermostat (1S37, if applicable) has closed.
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