SERVICING
The MBR contains an Electronic Blower Time Delay Relay board, B1370735. This board provides on/off time delays for the blower motor in cooling and heat pump heating demands when “G” is energized.
During a cooling or heat pump heating demand, 24Vac is supplied to terminal “G” of the EBTDR to turn on the blower motor. The EBTDR initiates a 7 second delay on and then energizes it’s onboard relay. The relay on the EBTDR board closes it’s normally open contacts and supplies power to the blower motor. When the “G” input is removed, the EBTDR initiates a 65 second delay off. When the 65 seconds delay expires the onboard relay is
During an electric heat only demand, “W1” is energized but “G” is not. The blower motor is connected to the normally closed contacts of the relay on the EBTDR board. The other side of this set of contacts is connected to the heat se- quencer on the heater assembly that provides power to the first heater element. When “W1” is energized, the sequencer will close it’s contacts within 10 to 20 seconds to supply power to the first heater element and to the blower motor through the normally closed contacts on the relay on the EBTDR. When the “W1” demand is removed, the sequencer opens it contacts within 30 to 70 seconds and removes power from the heater element and the blower motor.
The EBTDR also contains a speedup terminal to reduce the delays during troubleshooting of the unit. When this terminal is shorted to the common terminal, “C”, on the EBTDR board, the delay ON time is reduced to 3 seconds and the delay OFF time is reduced to 5 second.
Two additional terminals, M1 and M2, are on the EBTDR board. These terminals are used to connect the unused leads from the blower motor and have no affect on the board’s operation.
SEQUENCE OF OPERATION
This document covers the basic sequence of operation for a typical application with a mercury bulb thermostat. When a digital/electronic thermostat is used, the on/off staging of the auxiliary heat will vary. Refer to the installation instruc- tions and wiring diagrams provided with the MBR and AR*F for specific wiring connections and system con- figuration.
AR*F & MBR
WITH SINGLE STAGE CONDENSERS
1.0Cooling Operation
1.1On a demand for cooling, the room thermostat energizes “G” and “Y” and 24Vac is supplied to “Y” at the condensing unit and the “G” terminal on the EBTDR board.
1.2The compressor and condenser fan are turned on and after a 7 second on delay, the relay on the EBTDR board is energized and the blower motor starts.
1.3When the cooling demand “Y” is satisfied, the room thermostat removes the 24Vac from “G” and “Y”.
1.4The compressor and condenser fan are turned off and after a 65 second delay off, the relay on the EBTDR board is de- energized and the blower is turned off.
2.0Heating Operation
2.1On a demand for heat, the room thermostat energizes “W1” and 24Vac is supplied to heat sequencer, HR1, on the heater assembly.
2.2The contacts M1 and M2 will close within 10 to 20 seconds and turn on heater element #1. The normally closed contacts on the EBTDR are also connected to terminal M1. When M1 and M2 close, the blower motor will be energized thru the normally closed contacts on the EBTDR board. 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. If the first stage heat demand, “W1” cannot be satisfied by the heat pump, the temperature indoors will continue to drop. The room thermostat will then energize “W2” and 24Vac will be supplied to HR2 on the heater assembly. When the “W2” demand is satisfied, the room thermostat will remove the 24Vac from HR2. 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, “W2” will remain energized until the first stage demand “W1” is satisfied and then the “W1” and “W2” demands will be removed.
2.3When the “W1” heat demand is satisfied, the room thermostat will remove the 24Vac from HR1. Both set of contacts on the relay opens within 30 to 70 seconds and turn off the heater element(s) and the blower motor.
AR*F & MBR
WITH SINGLE STAGE HEAT PUMPS
3.0 Cooling Operation
On heat pump units, when the room thermostat set to the cooling mode, 24Vac is supplied to “O” which energizes the reversing valve. As long as the thermostat is set for cooling, the reversing valve will be in the energized position for cooling.
3.1On a demand for cooling, the room thermostat energizes “G” and “Y” and 24Vac is supplied to “Y” at the heat pump and the “G” terminal on the EBTDR board.
3.2The heat pump turned on in the cooling mode and after a 7 second on delay, the relay on the EBTDR board is energized and the blower motor starts.
3.3When the cooling demand is satisfied, the room thermo- stat removes the 24Vac from “G” and “Y”.
3.4The heat pump is turned off and after a 65 second delay off, the relay on the EBTDR board is
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