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MERIT
®
CBX25UHV SERIES
Table 11. Merit
®
CBX25UHV, Thermostat and Two‐Stage Outdoor Unit Operating Sequence
Operating Sequence System Demand System Response
System
Condition
Step
Thermostat Demand Relative Humidity
Com
pressor
Air
Handler
CFM
(COOL) CommentsY1 Y2 O G W1 W2 Status D
NO CALL FOR DEHUMIDIFICATION
Normal Operation
- Y1
1 On On On Acceptable 24 VAC Low 70%
Compressor and indoor air handler follow
thermostat demand
Normal Operation
- Y2
2 On On On On Acceptable 24 VAC High 100%
Room Thermostat Calls for First-Stage Cooling
BASIC MODE (only active on a Y1 thermostat demand)
Normal Operation 1 On On On Acceptable 24 VAC Low 70%
Thermostat energizes Y2 and de-ener
gizes D on a call for dehumidification
Dehumidification
Call
2 On On On On Demand 24 VAC High
60%/65%
70%*
PRECISION MODE (operates independent of a Y1 thermostat demand)
Normal Operation 1 On On On Acceptable 24 VAC Low 70%
Dehumidification mode begins when hu
midity is greater than set point
Dehumidification
Call
2 On On On On Demand 0 VAC High
60%/65%
70%*
Dehumidification
Call ONLY
1 On On On On Demand 0 VAC High
60%/65%
70%*
Thermostat will try to maintain room hu
midity setpoint by allowing the room
space to maintain a cooler room thermo
stat setpoint**
Room Thermostat Calls for First- and Second-Stage Cooling
BASIC MODE (only active on a Y1 thermostat demand)
Normal Operation 1 On On On On Acceptable 24 VAC High 100%
Thermostat energizes Y2 and de-ener
gizes D on a call for dehumidification
Dehumidification
Call
2 On On On On Demand 0 VAC High
60%/65%
70%*
PRECISION MODE (operates independent of a Y1 thermostat demand)
Normal Operation 1 On On On On Acceptable 24 VAC High 100%
Dehumidification mode begins when hu
midity is greater than set point
Dehumidification
Call
2 On On On On Demand 0 VAC High
60%/65%
70%*
Dehumidification
Call ONLY
1 On On On On Demand 0 VAC High
60%/65%
70%*
Thermostat will try to maintain room hu
midity setpoint by allowing the room
space to maintain a cooler room thermo
stat setpoint**
Jumpers at indoor unit with a two-stage outdoor unit
With Condensing unit - Y2 and R to O
With Heat Pump - none
* During dehumidification, cooling air handler speed is as follows: 70% of COOL cfm for 018, 024, 030; 65% for 036; 60% for 042, 048 and 060 units.
** Thermostat will maintain the room temperature up to 2°F (1.2°C) cooler than the room thermostat setting in precision mode.
HEAT JUMPER
The HEAT jumper is used to determine CFM during
electric heat operation only. These jumper selections are
activated only when W1 is energized.
DELAY JUMPER
The DELAY jumper is used to set the specific motor fan
operation during cooling mode. Depending on the
application, one of four options may be chosen by moving
the jumper to the appropriate set of pins.
#1 Pins Jumpered
A- Motor runs at 100% until demand is satisfied.
B- Once demand is met, motor ramps down to stop.
OFFOFF
A B
100% CFM
COOLING
DEMAND
#2 Pins Jumpered
A- Motor runs at 100% until demand is satisfied.
B- Once demand is met, motor runs at 100% for 60
seconds.
C- Motor ramps down to stop.
OF
OFF
A
B
C
100% CFM
100% CFM
(60 seconds)
COOLING DEMAND
#3 Pins Jumpered
A- Motor runs at 82% for approximately 7-1/2 minutes. If
demand has not been satisfied after 7-1/2 minutes -
B- Motor runs at 100% until demand is satisfied.
C- Once demand is met, motor ramps down to stop.
OFF
OFF
A
B
C
82%CFM
100% CFM
COOLING DEMAND
7 1/2 MIN
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