EMI Corp User Manual

Page 16

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Multi-zone Heat Pump Condensing Units

MULTI-ZONE CONDENSER SEQUENCE OF OPERATION

EMI America Series multi-zone heat pump

condensers are designed to operate with

EMI America Series indoor air handlers.

Both the condenser (outdoor unit) and

evaporator (indoor unit) have a high Volt

service connection. Each is to be indepen-

dently connected to the electrical service

panel. (See the unit name plate for the cor-

rect breaker type and size). The 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.

The S2HA is a limited range heat pump

that will provide comfort cooling or heat

pump operation operate at an outdoor tem-

perature range between 35°F and 115°F

for cooling, 35°F and 75°F for (heat pump)

heating. The outdoor unit is equipped

with a thermostat that will switch off the

condenser when temperature falls below

35°F. For heat pump mode the condenser

operation will cease and then switch on

the indoor electric heat. For cooling mode,

condenser operation will cease.

The S2HA limited range heat pump con-

densers are designed to operate as a

single stage cooling, two stage heating

unit. For full operation the unit should be

matched with an appropriate EMI indoor

unit with electric heat and unit mounted

controls or a wall mounted thermostat.

For two stage heating operation the indoor

unit must be equipped with an electric strip

heater.

See the instruction manual for the indoor

unit on the selection of the proper thermo-

stat for the system.

Condenser Operation:

The transformer located in the indoor unit

provides 24V, low-Volt control power to

the condenser (outdoor unit). This can be

measured across low-Volt terminals “R”

and “C”.

Heat pump condensers utilize a reversing

valve to provide reverse cycle operation.

Therefore the outdoor unit will act as ei-

ther a condenser or an evaporator 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, Multi-zone Heat

Pump:

Cooling mode operation requires that the

control (either unit mount or remote wall

mount thermostat) make a connection be-

tween low-Volt terminals “R” and “Y” along

with “R” and “O”. 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)

along with the compressor and outdoor fan

(R & Y). When the indoor control is satis

ﬁed and the room temperature falls below

the set temperature, the compressor and

fan will de-energize. The EMI indoor unit

is equipped with an anti-short cycle timer

(ASCT) will prevent the compressor from

re-starting for three minutes.

When the outdoor temperature falls below

35°F, compressor operation will cease.

Heating operation, Multi-zone Heat

Pump:

Heating mode operation requires that the

control (either unit mount or remote wall

mount 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 tem-

perature above room temperature, the

compressor and outdoor fan (R & Y) will

energize. When the indoor control is satis-

ﬁed and the room temperature rises above