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14-Burner Controls A3 & A12
Units have two burner controls. A3 controls gas heat sec-
gas heat section and the second gas heat section burner
controls are identical. Both burner controls are factory set
and are not adjustable. The control makes three attempts
at ignition and then locks out the system if ignition is not
obtained after the third trial. Reset after lockout requires
only breaking and remaking thermostat demand. The con-
or power failure. Upon restoration of gas and power, the
control will restart the ignition sequence and continue until
-
tailed description see the Gas Heat Components section.
15-Power Exhaust Relay K65 (PED units)
Power exhaust relay K65 is a N.O. DPDT relay with a
24VAC coil. K65 is used in units equipped with the op-
tional power exhaust dampers. K65 is energized by the
A55 Unit Controller, after the economizer dampers reach
50% open (adjustable in ECTO). When K65 closes, the
exhaust fans B10 and B11 are energized.
16-Blower Motor Overload Relay S42
-
-
ciency blower motors and M-volt unit blower motors man-
relay. The relay (S42) is connected in line with the blow-
the relay senses an overload condition, a set of normally
of the A55 Unit Controller. A55 de-energizes all outputs.
Units will be equipped with a relay manufactured by Tele-
17-Variable Frequency Drive A96 (optional)
Staged-Blower units are equipped with a VFD which alters
the supply power frequency and voltage to the blower mo-
tor. Blower speed is staged depending on the compressor
stages, heating demand, ventilation demand, or smoke
alarm.
-
rameters in the A55 Unit Controller. The VFD is located
below the Unit Controller.
18-VFD Power To Motor Contactor K202
(optional)
Contactor is used in Staged-Blower units equipped with
a VFD bypass option. The three-pole 40 amp contactor
with a 24VAC coil is energized by the A55 Unit Controller.
K202 allows power from the VFD to the B3 blower motor
in response to blower demand.
19-Inverter Start Forward Rotation Relay K203
(optional)
Relay is used in optional Staged-Blower units and is a
three-pole double-throw relay with a 24VAC coil. K203 is
energized by the A55 Unit Controller and provides input to
20-Unit Controller A55
The Unit Controller provides all unit control functions, unit
status information, unit diagnostics, programmable pa-
to the Unit Controller guide provided with the unit. Ther-
21-Compressor 3 & 4 Controller A59 & A178
outputs required for compressor and fan control, com-
pressor stage diagnostics and low ambient control. The
M3 unit controller is only compatible with L-Connection
sensors provided with the unit or purchased separately as
show thermistor and pressure transducer readings.
Temperature Sensors
The return air (RT16) and discharge air (RT6) duct probes
and the outdoor air (RT17) are all two wire thermistors.
The resistance vs. temperature table is shown below:
TABLE 1
Resistance vs. Temperature
Temp. °F (°C) Resistance +/-2% Temperature °F (°C) Resistance +/-2% Temp. °F (°C) Resistance +/-2%
-40 (-40) 335,671 40 (4.4) 26,106 7,332
50 (10) 100 (37.8) 5,826
0 (-17.8) 85,323 60 (15.6) 15,313 3,756
20 (-6.7) 46,218 70 (21.1) 11,884 130 (54.4) 3,047
30 (-1.1) 34,566 80 (26.7)
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