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31-5000751 Rev. 0
Unit Sequence of Operation
The following figures illustrate the overall unit sequence of operation along with the operation of various pressure switches
and temperature sensors. The figures also illustrate the use of the compressor anti-short-cycle function in relation to unit
Status, unit Fault and lockout LED Codes and unit system operation interactions.
Yes
No
Yes
No
Room thermostat provides a Y1 or Y2 demand to
the main control on systems with a conventional
24VAC thermostat
All switches closed
ing range.
Check for status or
fault codes in the
outdoor control or
room thermostat.
(
NOTE
- Refer to low
pressure and high
pressure switch flow
charts for sequence
of operation.
From idle mode
Outdoor Control
1. Sends a demand to the compressor
inverter to start and run the
compressor up to the requested
pumping capacity (Frequency in
hertz).
2. On NS18H units, output signal is
provided on PWM and COM terminals
to start and run the ECM outdoor fan
at the demand RPM
3. Sends a communication signal into
the indoor unit to start and run the
supply fan motor at the demand air
volume (CFM).
On 24 VAC power-up or outdoor reset, the outdoor control shall perform the following tasks:
1.
Start the anti-short cycle 3-minute delay in the outdoor control.
2.
Check status of the temperature sensor and pressure devices.
3.
If the outdoor control does not detect any error codes, outdoor control sends 24 volts out on the
CNTCTR terminals to pull in the contactor coil. (
Note
- These checks take about 60 seconds.
)
4.
The contactor contacts pull IN and main power is applied to the compressor inverter.
Figure 21. 24 Volt Power-Up or Outdoor Reset