Allied Air Enterprises 15), (2 Operation, Cooling, PSC Motor, Variable Speed Motor, and COOL Taps

OPERATION

Sequence of Operation

Cooling

Upon cooling demand, the thermostat closes circuit R and Y. Closing R and Y closes the unit contactor, starting the compressor and outdoor fan. The thermostat automatically closes R to G circuit which also brings on the indoor blower at the same time. Upon satisfying cooling demand, the thermostat will open the above circuits and open the main contactor, stopping the compressor and outdoor fan. If the unit is equipped with a delay timer, the blower will continue to operate for 90 seconds which improves system efficiency.

Circulating Air Blower

Depending on the package unit model, the blower motor will be either a multi-tap PSC motor or a variable speed motor.

PSC Motor

The circulating air blower is controlled by a timing circuit in the blower control. Timings are not adjustable.

There is no blower “on” delay after a call for heating or cooling. Blower “off” delay is 90 seconds after the thermostat is satisfied.

Variable Speed Motor

Units equipped with a variable speed circulation air blower motor will deliver a constant airflow within a wide range of external static pressures. Other features of this variable speed motor include:

Soft Start/Stop – The variable speed motor will slowly ramp up to normal operating speed. This minimizes noise and increases comfort by eliminating the initial blasts of air encountered with standard motors. At the end of a cooling or heating cycle, the motor will slowly ramp down.

Circulation Airflow Adjustments – The controls include a variable speed motor interface board. The ADJUST tap can be used to raise (+) or lower (–) the airflow by 15%.

Heating and Cooling Airflows – The units are factory set for the correct heating and cooling airflows. However, airflow changes can be made by moving the position of the HEAT and COOL taps (see Table 4).

Continuous Blower – The comfort level of the living space can be enhanced when using this feature by allowing continuous circulation of air between calls for cooling or heating. The continuous circulation of air occurs at half the full cooling airflow rate. To use this feature, place the thermostat fan switch into the ON position.

Cooling Airflow Ramp Up – At the beginning of a call for cooling, the blower will run at 80% of full airflow for 7.5 minutes. This improves the system’s moisture removal and saves blower power during cooling start.

Reduced Airflow Operation (Dehumidification) – For situations where humidity control is an issue, the variable speed motor can be connected to operate at a 25% reduction in the normal airflow rate. The variable speed motor interface board provides for connection of a humidistat on the HUM terminal. When a humidistat is connected, the dehumidifier resistor on the interface must be cut. The humidistat should be wired to open during high humidity, which will reduce blower airflow.

Adjusting Airflow (Variable Speed Motor Equipped Units Only)

Model

ADJUST, HEAT,

Nominal

Heating

Motor

ADJUST

HEAT

COOL

CFM

CFM

CFM

CFM

and COOL Taps

Cooling

Size

HP

Setting

Setting

Setting

A

B

C

D

and Dehumidify

Resistor

kBTU

kW

24

5-10

1/3

NORM

B

B

1000

800

600

900

on Interface

Board

30

5-10

1/3

NORM

A

A

1000

800

600

900

36

5-15

1/2

NORM

A

A

1200

1000

800

1100

ADJUST

HEAT

COOL

NORM

A

A

42

5-20

3/4

NORM

C

C

1800

1600

1400

1200

(+)

B

B

(–)

C

C

TEST

D

D

48

5-20

3/4

NORM

B

B

1800

1600

1400

1200

D1

60

5-20

3/4

NORM

A

A

1800

1600

1400

1200

DEHUMIDIFY

CUT TO ENABLE

Table 3

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