Carrier WEATHERMAKER 48/50AJ Operation And Service Manual page 43

then Lo Cool Mode mechanical stages = 2 and Hi Cool
Mode mechanical stages = 2.
5. If the economizer position is greater than Configuration
 
ECON EC.MX – 5% for more than 8 minutes but
less than 11.5 minutes and mechanical cooling has started
then:
Lo Cool Mode mechanical stages = 2
Hi Cool Mode mechanical stages = 3
6. If the economizer position is greater than Configuration
 
ECON EC.MX – 5% for more than 11.5 minutes and
mechanical cooling has started then:
Lo Cool Mode mechanical stages = 2
Hi Cool Mode mechanical stages = 3 (for 020 to 027
units only)
Hi Cool Mode mechanical stages = 4 (for 030 to 060
units only)
NOTE: If some compressors are not available due to being
faulted, the Hi Cool Mode number of compressors are affected
before the Lo Cool Mode number of compressors. For exam-
ple, if a 4 compressor unit has one compressor faulted, and the
economizer is not active, then an HVAC mode Hi Cool
requested number of compressors is changed from 4 to 3. If
another compressor faults, then both Lo Cool and Hi Cool
requested number of compressors are set to 2. In addition,
compressors cannot be brought on faster than one every
30 seconds. If the control needs to bring on 2 compressors at
once, the first compressor will come on followed by the second
compressor 30 seconds later.
Staging of compressors is shown in Tables 49-60.
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
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 ef-
fect, 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.
STAGE
0
COMP
A1 OFF
A2 OFF
B1 OFF
UNIT
020 0%
025 0%
027 0%
 
ALLM SA.L.O) cooling will
Table 51 — Staging Sequence without Hot Gas Bypass —
48/50AK,AY020-027 and Multi-Stage 48/50AJ,AW020-027
SEQUENCE 1
1 2 3
Compressor Status
ON ON OFF
OFF ON ON
OFF OFF ON
Unit Capacity 48/50A
33% 67% 67%
30% 65% 70%
33% 67% 67%
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 on page 50 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
SEQUENCE 1
STAGE
0 1
Thermostat Inputs
Y1 OPEN CLOSED CLOSED OPEN CLOSED CLOSED
Y2 OPEN OPEN
COMP Compressor Status
A1 OFF ON
A2 OFF OFF
B1 OFF OFF
UNIT Unit Capacity
020 0% 33%
025 0% 30%
027 0% 33%
Table 50 — 2-Stage Sequence —
48/50AJ,AW030-060
SEQUENCE 1
STAGE
0 1
Thermostat Inputs
Y1 OPEN CLOSED CLOSED OPEN CLOSED CLOSED
Y2 OPEN OPEN
COMP Compressor Status
A1 OFF ON
A2 OFF ON
B1 OFF OFF
B2 OFF OFF
UNIT Unit Capacity
030 0% 45%
035,036 0% 48%
040,041 0% 43%
050 0% 45%
051,060 0% 50%
4 0 1
ON OFF OFF
ON OFF ON
ON OFF OFF
100% 0% 33%
100% 0% 35%
100% 0% 33%
43
SEQUENCE 2
2 0 1
Thermostat Inputs
CLOSED OPEN OPEN
Compressor Status
ON OFF OFF
ON OFF ON
ON OFF OFF
Unit Capacity
100% 0% 33%
100% 0% 30%
100% 0% 33%
SEQUENCE 2
2 0 1
Thermostat Inputs
CLOSED OPEN OPEN
Compressor Status
ON OFF ON
ON OFF ON
ON OFF OFF
ON OFF OFF
Unit Capacity
100% 0% 45%
100% 0% 48%
100% 0% 43%
100% 0% 45%
100% 0% 50%
SEQUENCE 2
2 3
Compressor Status
ON ON
ON OFF
OFF ON
Unit Capacity 48/50A
67% 67%
65% 65%
67% 67%
2
CLOSED
ON
ON
ON
100%
100%
100%
2
CLOSED
ON
ON
ON
ON
100%
100%
100%
100%
100%
4
ON
ON
ON
100%
100%
100%