2-High Pressure Switch S4
The high pressure switch is an automatic reset SPST N.C.
the compressor discharge line and wired in series with the
compressor contactor coil.
opens and the respective compressor is de-energized
-
ergized. The CMC1 board monitors the pressure switch
in this condition. A pressure switch may open and close
again four times during a current demand cycle without
causing a lockout condition by resetting the count at the
strike lockout can only be reset by one of the following
-Power cycle the controller
-Apply the TEST mode
The low ambient switch is an auto-reset SPST N.O. pres-
sure switch which allows for mechanical cooling operation
at low outdoor temperatures. The switch is located in the
liquid line in the compressor section.
-
-
is de-energized. This intermittent fan operation results in
higher evaporating temperature allowing the system to op-
erate without icing the evaporator coil and losing capacity.
4-Compressor Low Discharge Temperature Limit S3
S3 is a thermostat which opens on temperature drop. It is
5-Compressor High Temperature Limit S5
The compressor thermal protector is located on top of the
C-Blower Compartment
All units are equipped with belt drive blowers. See unit
nameplate for blower type.
1-Blower Wheels
2-Indoor Blower Motor B3
-
front of this manual. Units may be equipped with motors
-
IMPORTANT
hree phase scroll compressors must be phased
sequentially for correct compressor and blower
rotation. Follow “COOLING START-UP” section
of installation instructions to ensure proper
compressor and blower operation.
A-Blower Operation
Initiate blower demand at thermostat according to instruc-
tions provided with thermostat. Unit will cycle on thermo-
stat demand. The following steps apply to applications
using a typical electro-mechanical thermostat.
1 - Blower operation is manually set at the thermostat
blowers will operate continuously.
2 -
cycle with demand. Blowers and entire unit will be
B-Determining Unit CFM
B-Determining Unit CFM
IMPORTANT - CFM
MUST BE ADJUSTED IN HIGH SPEED. Disconnect fac-
-
nectors are located near the bottom of the control box.
-
blower on low during ventilation only demands. See table
TABLE 4
TWO-SPEED BLOWER OPERATION
ZGB074S4T UNITS
Thermostat Blower Speed
High
High
High
High
*Factory-installed jack/plug connection.
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