SERVICING
rate programmed in the motor.
4.0 Heating Operation
On heat pump units, when the room thermostat is set to the heating mode, the reversing valve is not energized. As long as the thermostat is set for heating, the reversing valve will be in the
4.1On a demand for first stage heat with heat pump units, the room thermostat energizes “Y” and “G” and 24Vac is supplied to “G” and “Y/Y2” of the MBE. The VSTB will turn on the blower motor and the motor will ramp up to the speed programmed in the motor based on the settings of dip switch 1 and 2. The VSTB will supply 24Vac to “Y” at the heat pump and the heat pump is turned on in the heating mode.
4.2If the first stage heat demand cannot be satisfied by the heat pump, the temperature indoors will continue to drop. The room thermostat will then energize terminal “W2” for second stage heat and 24Vac will be supplied to “E/W1” of the MBE. The VSTB will supply 24Vac to heat sequencer, HR1, on the electric heater assembly.
4.3HR1 contacts M1 and M2 will close within 10 to 20 seconds and turn on heater element #1. At the same time, if the heater assembly contains a second heater element, HR1 will contain a second set of contacts, M3 and M4, which will close to turn on heater element #2.
Note: If more than two heater elements are on the heater assembly, it will contain a second heat sequencer, HR2, which will control the 3rd and 4th heater elements if available.
For the 3rd and 4th heater elements to operate on a third stage heat demand, the PJ4 jumper on the VSTB inside the MBE and AEP* must be cut. If the second stage heat demand, “W2”, cannot be satisfied by the heat pump, the temperature indoors will continue to drop. The room thermo- stat will then energize “W3” and 24Vac will be supplied to “W/ W2” of the MBE. The VSTB will supply 24Vac to HR2 on the electric heater assembly. When the “W3” demand is satis- fied, the room thermostat will remove the 24Vac from “W/W2” of the MBE and AEP*. The contacts on HR2 will open between 30 to 70 seconds and heater elements #3 and #4 will be turned off. On most digital/electronic thermostats, “W3” will remain energized until the first stage de- mand “Y” is satisfied and then the “G”, “Y”, “W2” and “W3” demands will be removed.
4.4As the temperature indoors increase, it will reach a point where the second stage heat demand, “W2”, is satisfied. When this happens, the room thermostat will remove the 24Vac from “E/W1” of the MBE. The contacts on HR1 will open between 30 to 70 seconds and turn off both heater element(s). The heat pump remains on along with the blower motor because the “Y” demand for first stage heat
will still be present.
4.5When the first stage heat demand “Y” is satisfied, the room thermostat will remove the 24Vac from “G” and “Y/ Y2” of the MBE and AEP*. The VSTB removes the 24Vac from “Y” at the heat pump and the heat pump is turned off. The blower motor will ramp down to a complete stop based on the time and rate programmed in the motor control.
5.0 Defrost Operation
On heat pump units, when the room thermostat is set to the heating mode, the reversing valve is not energized. As long as the thermostat is set for heating, the reversing valve will be in the
5.1The heat pump will be on and operating in the heating mode as described the Heating Operation in section 4.
5.2The defrost control in the heat pump unit checks to see if a defrost is needed every 30, 60 or 90 minutes of heat pump operation depending on the selectable setting by monitoring the state of the defrost thermostat attached to the outdoor coil.
5.3If the temperature of the outdoor coil is low enough to cause the defrost thermostat to be closed when the defrost board checks it, the board will initiate a defrost cycle.
5.4When a defrost cycle is initiated, the contacts of the HVDR relay on the defrost board open and turns off the outdoor fan. The contacts of the LVDR relay on the defrost board closes and supplies 24Vac to “O” and “W2”. The reversing valve is energized and the contacts on HR1 close and turns on the electric heater(s). The unit will continue to run in this mode until the defrost cycle is completed.
5.5When the temperature of the outdoor coil rises high enough to causes the defrost thermostat to open, the defrost cycle will be terminated. If at the end of the programmed 10 minute override time the defrost thermo- stat is still closed, the defrost board will automatically terminate the defrost cycle.
5.6When the defrost cycle is terminated, the contacts of the HVDR relay on the defrost board will close to start the outdoor fan and the contacts of the LVDR relay will open and turn off the reversing valve and electric heater(s). The unit will now be back in a normal heating mode with a heat pump demand for heating as described in the Heating Operation in section 4.
S-60 ELECTRIC HEATER (OPTIONAL ITEM)
Optional electric heaters may be added, in the quantities shown in the specifications section, to provide electric resistance heating. Under no condition shall more heaters than the quantity shown be installed.
The low voltage circuit in the air handler is factory wired and terminates at the location provided for the electric heater(s). A minimum of field wiring is required to complete the instal-
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