Unitary products group YMB Series Installation Manual Download Page 13

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170761-UIM-B-0406

Unitary Products Group

COOLING OPERATION

During cooling operation, the control will receive thermostat signals at
the Y1 and O input terminals. The control will energize the M compres-
sor output terminal. This signal energizes the coil of the compressor
contactor causing the compressor to run. The control also closes the
outdoor fan relay delivering power to the ODF terminal causing the out-
door fan to operate. The control energizes the RV terminal with 24VAC
to switch the reversing valve. Additionally, the Y2 Out terminal is ener-
gized with 24 VAC. This signal can be used to signal the indoor unit to
deliver high airflow.

HEATING OPERATION

During normal heating mode, the control will receive a thermostat signal
at the Y1 input terminal. The control will energize the M compressor
output terminal. This signal energizes the coil of the compressor con-
tactor causing the compressor to run. The control also closes the out-
door fan relay delivering power to the ODF terminal causing the outdoor
fan to operate. The reversing valve is not energized in heating mode. If
the Y2 terminal of the control is energized when the Y1 terminal is not
energized, the control will display and store a fault code and will not
energize the compressor.

Conventional Heat Pump Mode

The factory setting of the HOT HEAT PUMP jumper on the control is the
OFF position. In this configuration the heat pump operates in conven-
tional heat pump mode. If the jumper is not in place, the control will act
as if the jumper is in the OFF position.

If the HOT HEAT PUMP jumper is in the OFF position, the control will
energize the Y2 Out terminal whenever the compressor is running.

The location of the hot heat pump jumper is shown in Figures 10 and
13.

Hot Heat Pump Mode (With Variable Speed Blower)

The control will operate in Hot Heat Pump Mode only if the HOT HEAT
PUMP jumper on the control is placed in the ON position. The Y2 Out
signal must also be connected to the indoor unit.

The SWITCH POINT jumper on the control has no effect on the opera-
tion of the heat pump.

The control implements the Hot Heat Pump Mode by controlling the
indoor airflow level during heating operation only. Cooling operation is
not affected. By reducing the indoor airflow level, the heat pump system
will operate with increased indoor discharge air temperatures. The con-
trol changes the indoor airflow level using the Y2 Out signal. This termi-
nal is connected to the high speed cooling input of a variable speed
indoor unit. When the heat pump control energizes the Y2 Out terminal,
the indoor blower runs at high speed delivering high airflow. When the
control de-energizes the Y2 Out terminal, the indoor blower runs at a
lower speed delivering lower airflow.

If the HOT HP jumper is in the ON position and the control receives a
call for heating (Y1), the control will energize the compressor and mea-
sure the outdoor ambient temperature.

If the outdoor ambient temperature is equal to or greater than 50F, the
control will energize Y2Out and keep it energized until the thermostat is
satisfied (Y1 signal removed). The higher airflow is required to keep the
operating pressures low when the outdoor ambient temperature is 50F
or greater.

If the outdoor ambient temperature is less than 50F, the control will start
a ten-minute timer and keep Y2 Out de-energized. Therefore, the com-
pressor will be operating and the indoor unit will be operating with
reduced airflow. If the HOT HP jumper is in the ON position and if
the outdoor ambient temperature is less than 50F, the indoor air-
flow at the beginning of a heating cycle will always be low.

TABLE 9: Defrost Initiate Curves

Defrost Curve Selection

Jumper Position

Heat Pump Model

2-Ton

2.5-Ton

4-Ton
5-Ton

3-Ton

3.5-Ton

1.5-Ton

FIGURE 10: Defrost Operation Curves

REGION C