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SEQUENCE OF OPERATION
GENERAL
Operation of the unit heating and cooling cycles is automatic for HEAT and COOL functions. (The optional automatic changeover thermostat, when in the AUTO position, automatically changes to heat or cool with sufficient room temperature change.) The fan switch can be placed in either the ON position, causing continuous evaporator (indoor) fan operation, or the AUTO position causing fan operation to coincide with heating or cooling run cycles.
COOLING MODE
(NOTE: TSH & TSC are contacts internal to the indoor thermostat.)
With the disconnect switch in the ON position, current is supplied to the compressor crankcase heater and control transformer. (The outdoor fan relay (ODF) relay is energized through normally closed contacts on the defrost timer control (DFC) on the 460V and 600V units only.) The cooling cycle is enabled through the low voltage side of the control transformer to the “R” terminal on the indoor thermostat. With the system switch in the AUTO position and TSC- 1 contacts closed, power is supplied to the “O” terminal on the indoor thermostat to the switchover valve coil (SOV). This energizes the
When the indoor temperature rises
HEATING MODE
With the disconnect switch in the “ON” position, current is supplied to the compressor crankcase heater and control transformer. (The outdoor fan relay (ODF) is energized through normally closed contacts on the defrost timer control (DFC) on the 460V and 600V units.) Starting at the “R” terminal on the indoor thermostat, current goes through the system switch (which is in “AUTO” position) to the
SUPPLEMENTARY HEAT
The supplementary electric heat is brought on when the indoor temperature drops
When the indoor ambient is satisfied,
thermostat. When placed in the emergency heat position, it will disable the compressor, bypass the outdoor thermostats, if pro- vided, and engage the supplementary electric heaters and indoor fan.
DEMAND DEFROST OPERATION
During the heating cycle, the outdoor coil may require a defrost cycle which is determined by the demand defrost control (DFC). This control continuously measures the outdoor coil temperature (CBS) and the outdoor ambient temperature
ICM FAN MOTOR ADJUSTMENTS
If the airflow needs to be increased or decreased, see the Airflow Table in the Service Facts. Information on changing the speed of the blower motor is in the Blower Performance Table.
Blower speed changes are made on the ICM Fan Control mounted in the control box. The ICM Fan Control controls the variable speed motor.
There is a bank of 8 dip switches, (See Figure 15), located at the upper right side of the board. The dip switches work in pairs to match the cooling/heat pump airflow (CFM/TON), Fan
t | ICM FAN CONTROL | |
| CFM | DIP |
| SELECTION | |
| LIGHT | SWITCHES |
| DIP SWITCHES (TYPICAL SETTINGS) |
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