Page 52
XP17
Unit Sequence of Operations
The following figures illustrated the overall unit sequence of operations along with various pressure switches and
temperature sensor operations. These figures also illustration the use of the compressor anti-short cycle function in
relations to unit Status, Fault and Lockout LED Codes system operations interaction.
On 24VAC power-up or heat pump control (A175) reset, the heat pump control shall perform the
following tasks:
1. Start the anti-short cycle delay.
2. Check temperature sensor and pressure switches at the start of cooling demand.
3. Air Conditioner control responds to the thermostat input after the anti-short cycle timer expires. If there
is no thermostat input, control goes to standby mode.
Heat Pump control receives
cooling input.
The heat pump control (A175) will apply:
1. 24VAC to compressor contactor output Y1 OUT..
2. 24VAC to reversing valve output O terminal.
3. Output between 24 and 32 VDC on heat pump control's
ECM fan terminals ECM Y1 FAN and ECM C.
NOTE - If lower pressure switch is closed, system will ignore
for 90 seconds.
1. For low (S87) and high (S4) pressure switches sequence of operations, see figures 30 and 31.
2. For defrost calibration sequence of operations see figure 32.
3. For defrost sequence of operations see figure 32.
The outdoor fan control (A177) will:
Receive the DC voltage signal from the outdoor control (A175)
and converted the signal to a pulse width modulation (PWM)
signal. Jumper settings will determine fan PWM OUT fan speed.
NOTE — Refer to table 8 for jumper settings.
Room thermostat
calls for first stage?
Heat Pump control receives
heating input.
The heat pump control (A175) will apply:
1. 24VAC to compressor contactor output Y1 OUT..
2. Output between 24 and 32 VDC on heat pump
control's ECM fan terminals ECM Y1 FAN and
ECM C.
NOTE - If lower pressure switch is closed, system will
ignore for 90 seconds.
Figure 29. One-Stage Cooling/Heating Sequence of Operation
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