S1CG/S1HG
Single-Zone,
S2CG/S2HG
Dual-Zone
• Installation, Operation and Maintenance Manual •
P/N 240007754, Rev. C [3/19/2010]
31
Made in the USA
Single-zone and Dual-zone Condenser Sequence of Operation
EMI Series condensers are designed to operate
with EMI Series air handlers. Both the condens-
er (outdoor unit) and air handler (indoor unit)
have a high volt service connection. Each is to
be independently connected to the electrical
service panel. (See the unit name plate for the
correct breaker type and size). Th
e outdoor and
indoor units are also connected to each other
through a low volt interconnect wiring. A 24v
transformer located in the indoor unit provides
the low volt power source.
Straight cool condensers are designed to oper-
ate as a single stage cooling unit. Heat pump
condensers are designed to operate as a single
stage cooling two stage heating unit. For proper
operation the unit must be matched with an ap-
propriate EMI indoor unit with unit mounted
controls and/or wall mounted thermostat. For
two-stage heating operation the indoor unit
must be equipped with an electric strip heater.
NOTICE
For remote wall mounted thermostat
operation be sure to select EMI p/n
240008209 or a suitable 24v, two stage
heating, heat pump thermostat.
Condenser operation
The transformer located in the indoor unit
provides 24v, low-volt control power to the
condenser (outdoor unit). Th
is can be measured
across low-volt terminals “R” and “C”.
Heat pump condensers utilize a reversing valve
to provide reverse cycle operation. Th
erefore
the outdoor unit will act as either a condenser
or an air handler there-by providing comfort
cooling or heating to the indoor space. The
reversing valve is energized in cooling. Should
the valve fail to actuate, the system will default
to the heating mode of operation.
Cooling operation, single- and dual-zone
Cooling operation requires that the control
(either unit mount or remote wall mount ther-
mostat) make a connection between low-volt
terminals “R” and “Y” along with “R” and “O”
(heat pumps only). When the indoor control
is placed in cooling mode, with the set point
temperature below the room temperature, the
reversing valve will energize (R & O heat pumps
only) along with the compressor and outdoor
fan (R & Y). When the indoor control is satis-
fi ed and the room temperature falls below the
set temperature, the compressor and fan will
de-energize. Th
e anti-short cycle timer (ASCT)
will prevent the compressor from re-starting for
three minutes.
Heating operation
Heating operation requires that the control
(either unit mount or remote wall mount, heat
pump thermostat) make a connection between
low-Volt terminals “R” and “Y” only. When the
indoor control is placed in heating mode, with
the set point temperature above room tem-
perature, the compressor and outdoor fan (R
& Y) will energize. When the indoor control is
satisfi ed and the room temperature rises above
the set temperature, the compressor and fan will
de-energize. Th
e anti-short cycle timer (ASCT)
will prevent the compressor from re-starting for
three minutes.
Defrost controls with short cycle
protection (heat pumps only)
Th
e unit is equipped with a logic control circuit
designed to keep system operating at peek ef-
fi ciency. Th
e 24v circuit provides control to
the indoor and outdoor systems including a
three minute, anti-short cycle timer (ASCT)
compressor protection.
Th
e defrost control circuit is designed to keep
the condenser coil free from frost and ice during
heating mode. Th
is is accomplished through the
precise switching sequence of the outdoor fan,
reversing valve and indoor auxiliary heater.
Defrost initiation
Th
e defrost-sensor is located on either the end
plate or the return bend of the condenser coil.
A defrost cycle will initiate after the sensor
closes (approx. 30°F) and remains closed for
the length of time selected on the control board
(either 30, 60 or 90 minutes)*.
*Factory sett ings 9–24k Btu = 90 minutes
At the start of the defrost cycle, the reversing
valve will change from heating to cooling mode.
Th
e condenser fan will also switch off there-by
allowing pressure and temperature
