42
EDT Low Override
— There is an override if EDT drops too
low based on an alert limit that will lock out cooling. If the
supply air/evaporator discharge temperature (EDT) falls below
the alert limit (
Configuration
→
ALLM
→
SA.L.O
) cooling will
be inhibited. There is a 20-minute hold off on starting cooling
again once the following statement is true: EDT minus (
Run
Status
→
COOL
→
SUMZ
→
ADD.R
) has risen above
SA.L.O
.
The variable
ADD.R
is one of the SumZ cooling algorithm
control variables dedicated mainly for multi-stage control.
2-Stage Control and the Economizer
— The 2 stage logic will
first check for the availability of the economizer. If free cooling
can be used, then the control will first attempt to use the free
cooling.
If no mechanical cooling is active, and the economizer is
active, the economizer will first attempt to control to a cooling
control point of either the supply air set point high (
SA.HI
) or
supply air set point low (
SA.LO
) plus any reset applied,
depending on whether high cool or low cool mode is in effect,
respectively.
If one stage of mechanical cooling is on, and the economiz-
er is active, then the economizer will attempt to control to 53 F.
Also If HVAC mode = LOW COOL, the second stage of
mechanical cooling will be locked out.
If the set point cannot be satisfied or the economizer is not
active, then cooling will be brought on one stage at a time
when the evaporator discharge temperature (EDT) is greater
the 1.5° F above the current cooling control point. A start-up
time delay of 10 minutes and steady state delay after a com-
pressor is energized of 5 minutes is enforced.
If both circuits of mechanical cooling are running, then the
economizer will attempt to control to 48 F. If the economizer is
active and the outside air temperature (OAT) is less than the
cooling control point + 0.5 F, the compressors will be locked
off. When mechanical cooling is on, the control may also use
the economizer to trim the leaving-air temperature to prevent
unnecessary cycles of the compressor stages.
See the Economizer Integration with Mechanical Cooling
section for more information on the holding off of mechanical
cooling as well as the economizer control point.
Table 49 — 2-Stage Sequence —
48/50AJ,AW020-027
*Compressor start is delay 10 seconds from other compressor.
Table 50 — 2-Stage Sequence —
48/50AJ,AW030-060
*Compressor start is delay 10 seconds from other compressor.
Table 51 — Staging Sequence Without Hot Gas Bypass —
48/50AK,AY020-027 and Multi-Stage 48/50AJ,AW020-027
Table 52 — Staging Sequence With Hot Gas Bypass —
48/50AK,AY020-027 and Multi-Stage 48/50AJ,AW020-027
*With Minimum Load Valve ON.
STAGE
SEQUENCE 1
SEQUENCE 2
0
1
2
0
1
2
Thermostat Inputs
Thermostat Inputs
Y1
OPEN CLOSED CLOSED OPEN CLOSED CLOSED
Y2
OPEN
OPEN
CLOSED OPEN
OPEN
CLOSED
COMP
Compressor Status
Compressor Status
A1
OFF
ON
ON
OFF
OFF
ON
A2
OFF
OFF
ON*
OFF
ON
ON*
B1
OFF
OFF
ON
OFF
OFF
ON
UNIT
Unit Capacity
Unit Capacity
020
0%
67%
100%
0%
67%
100%
025
0%
65%
100%
0%
65%
100%
027
0%
67%
100%
0%
67%
100%
STAGE
SEQUENCE 1
SEQUENCE 2
0
1
2
0
1
2
Thermostat Inputs
Thermostat Inputs
Y1
OPEN CLOSED CLOSED OPEN CLOSED CLOSED
Y2
OPEN
OPEN
CLOSED OPEN
OPEN
CLOSED
COMP
Compressor Status
Compressor Status
A1
OFF
ON
ON
OFF
ON*
ON
A2
OFF
ON*
ON
OFF
ON
ON
B1
OFF
OFF
ON
OFF
OFF
ON*
B2
OFF
OFF
ON*
OFF
OFF
ON
UNIT
Unit Capacity
Unit Capacity
030
0%
45%
100%
0%
45%
100%
035,036
0%
48%
100%
0%
48%
100%
040,041
0%
43%
100%
0%
43%
100%
050
0%
45%
100%
0%
45%
100%
051,060
0%
50%
100%
0%
50%
100%
STAGE
SEQUENCE 1
SEQUENCE 2
0
1
2
3
4
0
1
2
3
4
COMP
Compressor Status
Compressor Status
A1
OFF
ON
ON
OFF
ON
OFF
OFF
ON
ON
ON
A2
OFF
OFF
ON
ON
ON
OFF
ON
ON
OFF
ON
B1
OFF
OFF
OFF
ON
ON
OFF
OFF
OFF
ON
ON
UNIT
Unit Capacity 48/50A
Unit Capacity 48/50A
020
0%
33%
67%
67%
100%
0%
33%
67%
67%
100%
025
0%
30%
65%
70%
100%
0%
35%
65%
65%
100%
027
0%
33%
67%
67%
100%
0%
33%
67%
67%
100%
STAGE
SEQUENCE 1
SEQUENCE 2
0
1
2
3
4
5
0
1
2
3
4
5
COMP
Compressor Status
Compressor Status
A1
OFF
ON*
ON
ON
OFF
ON
OFF
OFF
OFF
ON
ON
ON
A2
OFF
OFF
OFF
ON
ON
ON
OFF
ON*
ON
ON
OFF
ON
B1
OFF
OFF
OFF
OFF
ON
ON
OFF
OFF
OFF
OFF
ON
ON
UNIT
Unit Capacity 48/50A
Unit Capacity 48/50A
020
0%
18%
33%
67%
67%
100%
0%
18%
33%
67%
67%
100%
025
0%
17%
30%
65%
70%
100%
0%
22%
35%
65%
65%
100%
027
0%
21%
33%
67%
67%
100%
0%
21%
33%
67%
67%
100%
Summary of Contents for WEATHERMAKER 48AJ020
Page 95: ...95 Fig 13 Typical Main Control Box Wiring Schematic A48 7787 ...
Page 96: ...96 TO NEXT PAGE Fig 14 Auxiliary Control Box Wiring Schematic A48 7294 ...
Page 98: ...98 Fig 15 Typical 2 Stage Gas Heat Wiring Schematic Size 051 and 060 Units Shown A48 6866 ...
Page 102: ...102 TO NEXT PAGE Fig 18 Typical Power Schematic Size 051 and 060 Units Shown A48 7298 ...
Page 104: ...104 Fig 19 Controls Option Wiring Schematic A48 7810 ...
Page 105: ...105 Fig 20 Small Chassis Component Location Size 020 035 Units A48 7301 ...
Page 106: ...106 Fig 21 Large Chassis Component Locations Size 036 060 Units A48 7302 ...