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12−Blower Motor Overload Relay S42
S42 is a manual reset overload relay, used in all TCA units
equipped with 10 or more HP standard efficiency motors.
The relay is connected in line with the blower motor to mon-
itor the current flow to the motor. When the relay senses an
overload condition, a set of normally closed contacts opens
de−energizing the 24 volt output of T1. See figure figure 4.
13−Power Exhaust Relay K65 (PED units)
Power exhaust relay K65 is a DPDT relay with a 24VAC
coil. K65 is used in Y voltage units equipped with the
field installed optional power exhaust dampers. K65 is
energized by the economizer enthalpy control A6, after
the economizer dampers reach 50% open (adjustable)
When K65 closes, exhaust fans B10 and B11 are ener-
gized.
14−MCC Control A45
The main control module A45 (figure 6) controls all cool-
ing operation and serves as a staging point for all internal
inputs to the appropriate components of the TCA unit. The
MCC control receives and sends out 24 volts to the com-
ponents located in the TCA control box, economizer and
supply/return compartments. The control communicates to
compressors contactors K1, K2 , condenser fan relay K10 and
indoor blower contactor K3. Thermostat hook ups (TB1) and
low voltage hook ups (TB14) are located on the board. See
tables 2 and 3 for terminal designations. Tables 4, 5 , 6 and 7
show pin terminal designations.
Features
The MCC A45 is equipped with a green LED for board sta-
tus. See table 1 for LED flash codes. While in the cooling
mode the board will incorporate AUTO−STAGING. If the
board receives a Y3 demand (if applicable) the board will
energize Y1, Y2 and Y3 in successive order. In the same
manner a Y2, will be interpreted as a Y1/Y2. The MCC
control also incorporates a minimum run time of 4 minutes
for up to 3 independent cooling stages. This 4 minute run
time can be interrupted by pushing SW1 located on the
board. If pressed for 3 seconds or more, the control goes
into TEST mode disabling AUTO−STAGING. The MCC
control board is used for all T class units. A dip switch,
factory set, is provided to configure to unit type (TGA
gas, TCA cooling/electric heat, THA heat pump) See fig-
ure 5.
SIEMENS OVERLOAD RELAY
Adjust relay amp setting according to value given on the blower motor nameplate. Proper relay amp
setting equals motor nameplate FLA X service factor of 1.15 X .95.
Use small slotted screwdriver to adjust control mode from automatic reset (A) to manual reset (H).
Control must be in the manual reset mode (H) to perform a test. Press the red test button. Green trip
indicator should pop out. Press the blue reset screw to reset the relay.
BLUE RESET BUTTON IN
FACTORY-SET AUTO MODE
(Turn clockwise to H for
manual reset)
GREEN TRIP INDICATOR
(Flush with surface −− not tripped;
Above surface −− tripped)
AMP ADJUSTMENT DIAL
RED TEST BUTTON
FIGURE 4
