McQuay IM 660-3
3
Standard Control Features
Standard features of the MicroTech 2000 WSHP control
include:
•
Heating and cooling control from a room sensor
•
Monitoring of all equipment protection controls
•
Fan and compressor operation
•
Monitoring of discharge air temperature
•
Monitoring of leaving water temperature
•
Status of all vital unit functions
•
Optional control outputs
Additional standard features of the MicroTech 2000 control are
provided below.
Compressor Short Cycle Protection
When a compressor is energized, it remains energized for at
least 2 minutes before the temperature control sequence is
allowed to de-energize it. An alarm condition can override this
“minimum-on” timer and stop the compressor if necessary.
When a compressor is de-energized, it remains de-energized
for at least 5 minutes before the temperature control sequence
is allowed to energize it again.
Random Start
The random start feature prevents simultaneous compressor
startup that could otherwise occur after the following events:
•
Unit powerup
•
Unoccupied to occupied changeover
•
Brownout condition
The compressor start delay can be from 5 to 37 seconds and is
determined by the unique 48-bit Neuron chip ID.
Delayed Reversing Valve De-energization
This feature is provided to delay “swishing.” It prevents the
reversing valve from returning to its normal (cooling) position
for a period of approximately 10 seconds after the compressor
is re-energized when the unit is in the heating mode. If
necessary, an alarm condition can override the delay timer and
de-energize the reversing valve with the compressor.
Condensate Overflow Alarm
If a condensate overflow alarm is detected, the unit controller
immediately disables the compressor. Once the overflow alarm
disappears, the unit controller automatically resets the WSHP
unit. The condensate overflow sensor is an exposed ring
terminal located in the condensate drain pan. The condensate
overflow alarm occurs only when the unit is in cooling mode.
Brownout Alarm
The on-board brownout feature is meant to protect the
compressor contactors from low voltage or “brownout”
conditions. If the supply voltage to the water source heat
pumps is below 82% of the nameplate value, the WSHP
controller detects it, indicates it, and de-energizes the
compressor. After rectifying the brownout condition (when
supply voltage remains above 90% of nameplate) normal unit
operation resumes.
High Pressure Refrigerant Alarm
If excessive pressure in the refrigeration circuit is detected by
the high pressure switch, the compressor and reversing valve
de-energizes immediately. If the high pressure alarm
disappears, manually reset the unit controller by disconnecting
and reconnecting power to the unit.
Low Temperature Refrigerant Alarm
Upon detection of a low temperature refrigerant alarm, the unit
controller immediately puts the reversing valve in the cooling
position for 60 seconds. After 60 seconds, the compressor is
disabled. If the low temperature alarm disappears, manually
reset the unit controller by disconnecting and reconnecting
power to the unit. The low temperature alarm occurs only
when the unit is in heating mode.
Low Pressure Refrigerant Alarm
Upon detection of a low pressure refrigerant alarm, the unit
controller immediately disables the compressor. If the low
pressure alarm disappears, manually reset the unit controller
by disconnecting and reconnecting power to the unit.
Change Filter Notification (network units
only)
When the water source heat pump fan run time exceeds a
network-adjustable set point, a change filter notification is
indicated locally and over the MicroTech network.