Unit Controls
EVAPORATOR PUMP CONTROL
The evaporator pump dry contacts (CTB2 - terminals 23 - 24) are energized when any of the following condi- tions are true:
1.Low Leaving Chilled Liquid Fault
2.Any compressor is running
3.Daily Schedule is not programmed OFF and Unit Switch is ON.
The pump will not run if the micro panel has been pow- ered up for less than 30 seconds or if the pump has run in the last 30 seconds to prevent pump motor overheat- ing.
EVAPORATOR HEATER CONTROL
The evaporator heater is controlled by ambient air tem- perature. When the ambient temperature drops below 40°F (4.4°C) the heater is turned on. When the tem- perature rises above 45°F (7.2°C) the heater is turned off. An under voltage condition will keep the heater off until full voltage is restored to the system.
CONDENSER FAN CONTROL
Condenser fan operation must be programmed with the Options key under “Fan Control.” Condenser fan con- trol can be selected for Ambient Temp. and Disch. Pres- sure, or Discharge Pressure Only.
The condenser fan control by “Ambient Temperature and Discharge Pressure” is a feature that is integral to the standard software control. If the optional discharge transducer is not installed, the condenser fans will op- erate based on outdoor ambient temperature only. See Table 39.
The condenser fan control by “Discharge Pressure” is a feature that can be selected if the discharge pressure transducer is installed and fan recycling is not a con- cern. Fan control by discharge pressure will work ac- cording to Table 40. The fan control
TABLE 39 – CONDENSER FAN CONTROL USING OUTDOOR AMBIENT TEMPERATURE AND DISCHARGE PRESSURE
FAN STAGE | ON | OFF | |
1 | OAT >25° F | OAT < 20° F | |
OR | AND | ||
1 FAN FWD | |||
DP > ctrl_press | DP < ctrl_press - diff_press | ||
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2 | OAT >45° F (7.2°C) | OAT < 40° F (4.4°C) | |
OR | AND | ||
2 FANS FWD | |||
DP > ctrl_press + 20 PSIG (1.38 Bars) | DP < ctrl_press - diff_press + 20 PSIG (1.38 Bars) | ||
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TABLE 40 – CONDENSER FAN CONTROL USING DISCHARGE PRESSURE ONLY
FAN STAGE | ON | OFF |
1 | DP > ctrl_press | DP < ctrl_press - diff_press | |
1 FAN FWD | |||
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2 | DP > ctrl_press + 20 PSIG | (1.38 Bars) DP < ctrl_press - diff_press + 20 PSIG (1.38 Bars) | |
2 FANS FWD | |||
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90 | YORK INTERNATIONAL |
