Controls
Control sequence
Standby —
During unit off cycle when the RUN/STANDBY
switch is in the STANDBY position, the crankcase heaters
and the control system are energized.
NOTE: The control circuit power must be on at all times
even when the main unit power is off.
Run —
When the RUN/STANDBY switch is moved from
STANDBY to RUN position, there will be a 1
1
⁄
2
minute de-
lay while the microprocessor monitors data. If in occupied
mode, after 1
1
⁄
2
minutes the chilled fluid pump will start. If
there is a call for cooling, the first compressor will start un-
loaded. The first circuit to start may be circuit A or B due to
the automatic and random lead/lag feature.
Capacity control sequence
On a call for cooling, the control system starts the initial
compressor. The control will randomly select either circuit
A or B. The liquid line solenoid valve remains closed for 10
seconds after the initial compressor on that refrigeration
circuit starts (unless the compressor has run in the 15 min-
utes prior to the latest call for cooling). This permits a pum-
pout cycle at start-up to minimize refrigerant floodback to
the compressor. If the compressor has run in the 15 min-
utes before the call for cooling, the pumpout cycle is
eliminated.
After the pumpout, the liquid line solenoid valve and the
EXV open.
The EXV will open gradually to provide a controlled
start-up to prevent liquid floodback to the compressor. Also
during this period, the oil pressure switch will be bypassed
for one minute.
As additional cooling is required, the control system will
ramp up through the capacity steps available until the load
requirement is satisfied. As capacity steps are added, com-
pressors are added, alternating between the lead and lag
refrigerant circuits. The speed at which capacity is increased
or decreased is controlled by the temperature deviation from
the set point and the rate of change in the chilled fluid
temperature.
When the second or lag refrigeration circuit is started,
that circuit will go through a 10-second pumpout unless the
circuit has been operating in the 15 minutes prior to this
start.
Upon load reduction, the control system will unload the
unit in the reverse order of loading until the capacity nearly
matches the load. Each time the lead compressor in a cir-
cuit is cycled off, the liquid solenoid valve and EXV will be
closed for 10 seconds prior to compressor shutdown to clear
the cooler of liquid refrigerant.
To stop unit, move the RUN/STANDBY switch to the
STANDBY position. Any refrigeration circuit that is oper-
ating at this time will continue to run for 10 seconds to
complete the pumpout cycle.
CAPACITY CONTROL STEPS
UNIT
30HR,
30HS
CONTR
STEPS
SEQUENCE A
SEQUENCE B
%
Disp.
Oper Cylinders
%
Disp.
Oper Cylinders
Tot.
Ckt A
Ckt B
Tot.
Ckt A
Ckt B
Compr
Compr
A1 A2 B1 B2
A1 A2 B1 B2
070
1
14.3
2
2
—
—
—
28.6
4
—
—
4
—
2
42.9
6
2
—
4
—
42.9
6
2
—
4
—
3
57.2
8
2
—
6
—
57.2
8
4
—
4
—
4
71.2
10
4
—
6
—
71.2
10
4
—
6
—
5
85.7
12
2
4
6
—
85.7
12
2
4
6
—
6
100.0
14
4
4
6
— 100.0
14
4
4
6
—
080
1
25.0
4
4
—
—
—
25.0
4
—
—
4
—
2
50.0
8
4
—
4
—
50.0
8
4
—
4
—
3
62.5
10
4
—
6
—
62.5
10
6
—
4
—
4
75.0
12
6
—
6
—
75.0
12
6
—
6
—
5
87.5
14
4
4
6
—
87.5
14
4
4
6
—
6
100.0
16
6
4
6
— 100.0
16
6
4
6
—
090
1
22.2
4
4
—
—
—
22.2
4
—
—
4
—
2
44.4
8
4
—
4
—
44.4
8
4
—
4
—
3
55.5
10
4
—
6
—
55.5
10
6
—
4
—
4
66.7
12
6
—
6
—
66.7
12
6
—
6
—
5
88.8
16
4
6
6
—
88.8
16
4
6
6
—
6
100.0
18
6
6
6
— 100.0
18
6
6
6
—
100
1
20.0
4
4
—
—
—
20.0
4
—
—
4
—
2
40.0
8
4
—
4
—
40.0
8
4
—
4
—
3
50.0
10
4
—
6
—
50.0
10
6
—
4
—
4
60.0
12
6
—
6
—
60.0
12
6
—
6
—
5
70.0
14
4
4
6
—
70.0
14
6
—
4
4
6
80.0
16
6
4
6
—
80.0
16
6
—
6
4
7
90.0
18
4
4
6
4
90.0
18
6
4
4
4
8
100.0
20
6
4
6
4
100.0
20
6
4
6
4
110
1
18.2
4
4
—
—
—
18.2
4
—
—
4
—
2
36.3
8
4
—
4
—
36.3
8
4
—
4
—
3
45.4
10
4
—
6
—
45.4
10
6
—
4
—
4
54.5
12
6
—
6
—
54.5
12
6
—
6
—
5
72.7
16
4
6
6
—
63.6
14
6
—
4
4
6
81.8
18
6
6
6
—
72.7
16
6
—
6
4
7
90.9
20
4
6
6
4
90.9
20
6
6
4
4
8
100.0
22
6
6
6
4
100.0
22
6
6
6
4
120,
160
1
16.6
4
4
—
—
—
16.6
4
—
—
4
—
2
33.3
8
4
—
4
—
33.3
8
4
—
4
—
3
41.6
10
4
—
6
—
41.6
10
6
—
4
—
4
50.0
12
6
—
6
—
50.0
12
6
—
6
—
5
66.7
16
4
6
6
—
66.7
16
6
—
4
6
6
75.0
18
6
6
6
—
75.0
18
6
—
6
6
7
91.6
22
4
6
6
6
91.6
22
6
6
4
6
8
100.0
24
6
6
6
6
100.0
24
6
6
6
6
140
1
19.0
4
4
—
—
—
19.0
4
—
—
4
—
2
38.0
8
4
—
4
—
38.0
8
4
—
4
—
3
47.6
10
4
—
6
—
47.6
10
6
—
4
—
4
57.0
12
6
—
6
—
57.0
12
6
—
6
—
5
69.0
16
4
6
6
—
69.0
16
6
—
4
6
6
78.6
18
6
6
6
—
78.6
18
6
—
6
6
7
90.4
22
4
6
6
6
90.4
22
6
6
4
6
8
100.0
24
6
6
6
6
100.0
24
6
6
6
6
LEGEND
Ckt
— Circuit
Compr
— Compressor
CONTR — Control
Disp.
— Displacement
Oper
— Operating
Tot
— Total
NOTE: Circuits and compressors designated from left to right when viewed from
front of unit.
31