17
IOM, WD Models
Enertech Global
Sequence of Operation
The description below is based on water-to-water units with a
double compressor.
Timings assume the ASC timer is expired. If the ASC timer
is not expired the accessory, compressor, and loop pump
operation do not start until the ASC timer is expired.
Components are sequenced and delayed for reduction in
surge current, and to reduce startup noise of the system. The
WD240 and 360 have staged compressors controlled with
separate Y1 and Y2 inputs. The CC output of the controller
energizes the first compressor contactor and begins the
time-out relay (adjustable 10 to 1000 seconds; factory set at
10). After the time-out delay, A Y2 input can energize the 2nd
compressor contactor.
Note: Ensure there is always a delay time between the
operations of the two compressors to avoid nuisance low-
pressure lockouts.
Heating 1st Stage, (Y1)
The Accessory (A) terminal output is energized after the
random start timer (10s-20s) expires (to provide time for
external pumps to provide adequate water flow prior to the
system starting). Next, after another 10s delay, the compressor
first stage and the loop pump(s) are energized.
Heating 2nd Stage, (Y1, Y2)
After the adjustable time delay relay expires and a Y2 call is
received, the second compressor is energized.
Cooling Operation
The reversing valve is energized for cooling operation. Terminal
“O” from the thermostat is connected to the reversing valve
solenoid.
Cooling 1st stage (Y1, 0)
The Accessory (A) terminal output is energized after the
random start timer (10s-20s) expires then the first stage
compressor and the loop pump(s) are energized 10 seconds
after A.
Cooling 2nd Stage (Y1, Y2, 0)
After the adjustable time delay relay expires and a Y2 call is
received, the second compressor is energized.
Section 7: Controls