FORM 145.16-IOM2 (0611)
JOHNSON CONTROLS 11
UNIT CONTROLS
The control system microprocessor board is
specifically designed for water source heat pump
operation. The control system interfaces with a
conventional type thermostat.
• Unit shall be complete with self-contained
low-voltage control circuit
• Unit shall incorporate a lockout circuit which
provides reset capability at the space
thermostat or base unit, should any of the
following standard safety devices trip and
shut off compressor.
- Loss-of-charge/Low-pressure switch
- High-pressure switch
- Freeze-protection thermostat, unit
shutdown on low water temperature.
- Condensate Overflow protection switch
• Unit shall operate with conventional
thermostat designs and have a low voltage
terminal strip for easy hook-up.
• Unit control board shall have on-board
diagnostics and fault code display.
• Standard controls shall include anti-short
cycle and low voltage protection
• Control board shall monitor each refrigerant
safety switch independently.
• Control board shall have random start feature
• Control board shall retain last 5 fault codes in
non volatile memory which will not be lost in
the event of a power loss.
Operation
For cooling the room t-stat energizes the low-
voltage circuit between “R” & “Y1”.
The call is passed to the unit microprocessor
control, which then determines whether the
requested operation is available and, if so, which
components to energize.
For the heating, the room t-stat energizes the
circuit between “R” & “W1”. The microprocessor
control energizes the compressor and fan
allowing the unit to run in heating mode.
If at any time a call for both heating and cooling
are present, the heating operation will be
performed. If operating, the cooling system is
halted as with a completion of a call for cooling.
Heating always takes priority.
Continuous Blower
By setting the room t-stat fan switch set to “ON”,
the supply air blower will operate continuously.
With the room t-stat fan switch set to “AUTO” or
“HEAT” settings, the blower is energized
whenever a cooling or heating operation is
requested. The blower is energized after any
specified delay associated with the operation.
When energized, the indoor blower has a
minimum run time of 30 seconds. Additionally, the
indoor blower has a delay of 10 seconds between
operations.
When the room t-stat calls for cooling, the low-
voltage control circuit from “R” to “Y1”and “G” is
completed. The compressor and fan motor are
energized. After completing the specified fan on
delay for cooling, the microprocessor control will
energize the blower motor.
Once the room t-stat has been satisfied, it will de-
energize “Y1”. If the compressor has satisfied its
minimum run time, the compressor and fan de-
energize. Otherwise, the unit operates the cooling
system until the minimum run time for the
compressor has been completed. After the
compressor de-energizes, the blower is stopped
following the elapse of the fan-off delay for
cooling.
To be available, a compressor must not be
locked-out due to a high-pressure switch; low-
pressure switch; condensate overflow switch;
freezestat trip; and the anti-short cycle delay
(ASCD) must have elapsed.
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