McQuay MicroTech II Operation & Maintenance

Page 28 of 32 OM 750
SPACE TEMP SENSOR FAILURE ( )
The Space Temp Sensor Failure fault will occur when the UVC detects
an open or a short condition from the space temperature sensor.
Effect:
• Space fan is de-energized (unless in emergency heat mode)
• Compressor is immediately de-energized
• Outdoor fan (if present) is de-energized
• Outside air damper is forced closed
• Electric heat stages are de-energized
• Fault is indicated
DX PRESSURE FAULT ( )
The DX Pressure Fault will occur when the UVC detects a switch open
condition from the refrigerant pressure switch.
Effect:
• Compressor is immediately de-energized
• Outdoor fan (if present) is de-energized
• Fault is indicated
COMPRESSOR ENVELOPE FAULT ( )
The UVC monitors refrigerant temperatures. The Compressor Envelope
Fault will occur when the UVC detects compressor operation that has
exceeded the allowed operating parameters.
Effect:
• Compressor is immediately de-energized
• Outdoor fan (if present) is de-energized
• Fault is indicated
Cause:
• Poor air flow through the refrigerant coils, check fans for proper
RPM, check air filters
• If the unit has a 3-phase scroll compressor, check for proper
electrical phasing
• Refrigerant circuit component failure or improper adjustment, check
refrigerant pressures and TXV adjustment
• Coil sensors may have lost proper contact with the refrigerant coil,
check coil sensors
DISCHARGE AIR DX COOLING LOW
LIMIT INDICATION ( )
The Discharge Air DX Cooling Low Limit Indication will occur when
the UVC detects a low discharge air temperature (DAT < MCLL)
during compressor cooling.
Effect:
• Compressor is immediately de-energized
• Outdoor fan (if present) is de-energized
• Fault is indicated
CONDENSATE OVERFLOW INDICATION (OPTIONAL) ( )
The Condensate Overflow Indication (optional) will occur when the
UVC detects high condensate levels within the units indoor coil drain pan.
Effect:
• Compressor is immediately de-energized if in cooling
• Outdoor fan (if present) is de-energized
• Fault is indicated
SPACE COIL DX TEMP SENSOR FAILURE ( )
The Space Coil DX Temp Sensor Failure fault will occur when the UVC
detects an open or a short condition from the DX temperature sensor.
Effect:
• Compressor is immediately de-energized
• Outdoor fan (if present) is de-energized
• Fault is indicated
OUTDOOR TEMP SENSOR FAILURE ( )
The Outdoor Temp Sensor Failure fault will occur when the UVC
detects an open or a short condition from the OA temperature sensor.
Effect:
• Compressor is immediately de-energized
• Outside air damper is forced closed
• Fault is indicated
DISCHARGE AIR TEMP SENSOR FAILURE ( )
The Discharge Air Temp Sensor Failure fault will occur when the UVC
detects an open or a short condition from the DA temperature sensor.
Emergency heat mode is available during this fault condition.
Effect:
• Space fan is immediately de-energized (unless in emergency heat
mode)
• Compressor is immediately de-energized
• Outdoor fan (if present) is immediately de-energized
• Outside air damper is forced closed
• Electric heat stages are de-energized
• Fault is indicated
OUTDOOR COIL DX TEMP SENSOR FAILURE ( )
The Outdoor Coil DX Temp Sensor (air source self-contained type units
– AZ and AE only) Failure fault will occur when the UVC detects an open
or a short condition from the OA DX temperature sensor.
Effect:
• Compressor is immediately de-energized
• Outdoor fan (if present) is de-energized
• Fault is indicated
SPACE HUMIDITY SENSOR FAILURE (OPTIONAL) ( )
The Space Humidity Sensor Failure fault will occur when the UVC
detects an open or a short condition from the IA space humidity sensor.
Effect:
• IA/OA Enthalpy comparison economizer (if used) is disabled
• Dehumidification function (optional) is disabled
• Fault is indicated
OUTDOOR HUMIDITY SENSOR FAILURE (OPTIONAL) ( )
The Outdoor Humidity Sensor Failure fault will occur when the UVC
detects an open or a short condition from the OA humidity sensor.
Effect:
• IA/OA Enthalpy comparison or OA Enthalpy economizer (if used)
is disabled
• Fault is indicated
DIAGNOSTICS AND SERVICE (continued)

McQuay MicroTech II Specifications

General

Brand	McQuay
Model	MicroTech II
Category	Controller
Language	English