56 AGZ 030A through 065A IOM 686
Table 20, Relay Board Outputs
Digital Output
Number
Output
Description
0 Alarm Circuit
1 Chilled Water Pump Relay
2 Liquid Line Solenoid Circuit #1
3 Liquid Line Solenoid Circuit #2
4 Compressor #1 Circuit #1
5 Compressor #2 Circuit #2
6 Hot Gas Bypass Circuit #1
7 Hot Gas Bypass Circuit #2
8 Compressor #3 Circuit #1
9 Compressor #4 Circuit #2
10 Condenser Fan (M11)
11 Condenser Fan (M12)
12 Spare
13 Condenser Fan (M21)
14 Condenser Fan (M22)
15 Spare
Reset Options
User reset options are located in the “Leaving Water Setpoint” menu. The options are:
None
“None” is the default value and the leaving evaporator water temperature controls the unit.
Return
When selecting “Return” as the reset mode, the controller resets the leaving water temperature set
point as required to maintain the selected return water temperature.
4 - 20 mA (remote reset signal)
When selecting “4-20mA” as the reset mode, the controller will reset the leaving water temperature to
a higher value based on a percentage of the “Maximum Chilled Water Reset”. At 4mA or less, the
leaving water temperature is not reset. At 20mA the leaving water temperature is reset to the
maximum. Between 4 and 20 mA, the leaving water temperature is reset proportionally to the reset
input signal.
Outside Air
When selecting “Outside Air” as the reset mode, the controller will reset the leaving water temperature
to a higher value based on the temperature of the outside air (ambient). As the outside air temperature
decreases, the leaving water temperature is reset up until the maximum reset is obtained. When the
outside air temperature is above the outside air temperature reset setpoint the leaving water
temperature is not reset and is controlled to the leaving water temperature setpoint.
Ice (for lower ice setpoint requirements, consult McQuay Marketing Support)
When in “Ice” reset mode, and adequate amount of glycol must be added to the system to protect the
evaporator from freezing. McQuay recommends a minimum of 30% solution of ethylene glycol to
protect to 7° F with the minimum leaving water temperature at unit shut down of 21°F. At 21°F shut
down, the saturated refrigerant temperature can approach 10°F.
The leaving water setpoint must be calculated according to the following formula;
LvgEvapSpt = Desired Ice Temperature + 1/2 Control Band + Shut down Delta T
Lvg EvapSpt = 21°F + 1/2 (4)°F + 1.5°F
Lvg Evap Spt = 21°F + 2°F + 1.5°F
Lvg Evap Spt = 24.5°F
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