OPERATING SEQUENCE
Base Unit Controls —
Indoor (Supply) Fan
The indoor fan contactor (IFC) is remotely located at the fan coil or fan section. If the thermostat fan operation is selected as Continuous, the IFC is energized and the indoor (supply) fan motor runs continuously. If the thermostat fan operation is selected as Automatic, the IFC will be energized on a call for Cooling or Heating; indoor (supply) fan motor runs. When thermostat is satisfied, the IFC is
Cooling, Unit Without Economizer
When thermostat calls for Cooling, terminal Y1 is energized. The 38AUQ’s Defrost Board (DFB) receives this input at
Output
When space cooling load is satisfied, terminal Y1 is
If either the Loss of Charge (LOC) Switch or High Pressure Switch (HPS) opens while Y1 remains energized, the compres- sor contactor C and relay SVR are
Reversing valve solenoid (RVS) is energized in Cooling modes. This solenoid will remain energized until the next Heat- ing mode is initiated.
Cooling, Unit With Economizer
Refer to fan coil unit installation instructions and economizer accessory installation instructions for operating sequences when system is equipped with accessory economizer.
Heating
When the thermostat calls for first stage heating, terminal W1 is energized. The 38AUQ’s Defrost Board (DFB) receives this input at
DFB issues outputs at OF and
Output
Solenoid Valve Relay SVR and compressor contactor C.SVR contacts close, energizing the external liquid line solenoid valve. Solenoid valve LLSV opens. Compressor contactor C closes, energizing the compressor motor. Compressor starts and system runs in Heating mode, providing Stage 1 Heat.
When the space heating load is satisfied terminal W1 is
If either the Loss of Charge (LOC) Switch or High Pressure Switch (HPS) opens while, the compressor contactor C and re- lay SVR are
Reversing valve solenoid remains
Defrost Cycle
During the Heating Mode, frost and ice can develop on the out- door coil. Defrost sequence will clear the frost and ice from the coil by briefly reversing the Heating sequence periodically.
A window to test for a need to run the Defrost cycle opens at a fixed period after the end of the last Defrost cycle or the previ- ous test window closed. The window period is determined by the configuration settings on the DFB’s DIP switches (see unit wiring diagram).
If the outdoor coil’s Defrost Thermostat switch (DFT) is closed (shorting DFB terminals DFT1 and DFT1), the Defrost cycle will start. Output at OF is removed; outdoor fans stop during the Defrost cycle. Output
During the Defrost cycle, output EHEAT is also energized (if not already energized by a thermostat W2 demand); supple- mental heater will be energized. During the Defrost Cycle, LED1 on the DFB will be illuminated. The Defrost cycle ends when DFT opens (as liquid temperature exiting the coil rises above DFT setpoint) or the defrost cycle runs for 10 minutes. Output at EHEAT is removed; supplemental heater will be
Defrost cycle is fixed at a maximum 10 minute duration limit. The period to test and initiate a Defrost cycle can be configured for 30, 60, 90 or 120 minutes.
Supplemental Heat/Emergency Heat
Supplemental heat type is determined by 40RUQ indoor unit options and accessories. This heat is initiated when the indoor unit W2 terminal is energized by the thermostat. (Or as detailed in “Defrost Cycle” on page 19.) The thermostat may energizes W2 as supplemental (2nd stage) heat at larger space heating de- mand, or when selected as emergency heat mode. When the space heating demand decreases below the 2nd stage limit, or emergency heat is turned off, W2 is
Cooling and Heating Shutdown
Partial or complete cooling or heating functions may shutdown caused by loss of main power, open pressure switches, diag- nostic alarms, or open internal compressor protections. See Service section for further details.
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