Pressure Below Band — Quincy Q-Command / Q-Command 4.0 sequencer Fault Code

Quincy Q-Command / Q-Command 4.0 sequencer

Use the built-in trending to document unloaded run hours before and after sequencing — that report is usually what justifies the panel to the customer.

Manufacturer

Quincy

Display

Color touchscreen (Q-Command 4.0); text LCD on earlier Q-Command panels.

Years produced

~2010 – present.

Power supply

100 – 240 VAC wall-mount panel, internal 24 VDC bus.

Ambient range

0 – 50 °C.

Protection rating

NEMA 4 / IP54 enclosure options.

Relay outputs

Per-compressor enable relays, dryer enable, common alarm.

Used on

Mixed Quincy fleets
Third-party compressors via contact or Modbus interface

Features

Pressure-band sequencing with rotation on run hours
VSD trim management so only one variable machine modulates
Energy and specific-power reporting for audits
Scheduled pressure setpoints for off-shift savings

Interfaces

Ethernet Modbus TCP
RS-485 Modbus RTU
Web dashboard on 4.0
Email/SMS alarm notification on 4.0

Sensor inputs

System header pressure (primary and backup)
Flow / dew point (option)
Per-compressor status via Modbus or dry contacts

Fault code lookup

Compressor Offline / Comm Fault A machine stopped answering the master.

First checks

Unique slave address
Bus termination at both physical ends only
Machine must be in Remote mode

See trigger conditions & affected models →

System Pressure Transducer Fault Header sensor open or out of range.

First checks

4–20 mA loop check
Sense line valve closed
Compare with calibrated gauge

See trigger conditions & affected models →

Pressure Below Band Not enough capacity online.

First checks

Machines locked out or in Local
Standing alarms on slaves
Check for a large new leak or a stuck-open drain

See trigger conditions & affected models →

Backup Control Active Master handed off to hardwired backup switches.

First checks

Check master power and network
Verify backup switch setpoints

See trigger conditions & affected models →

Fault list is non-exhaustive and firmware-dependent. Always confirm against the controller’s on-screen help or OEM manual.

Sensor pin resistance & signal values

Pin-level resistance and signal values for the sensor types this controller uses. Works offline. De-energise the panel and lift one lead before ohming any element.

Wiring notes

Every slave must be switched to Remote/Sequenced at its own controller before the master can command it
Run the Modbus trunk in dedicated conduit away from starter and VFD wiring
Always keep a hardwired backup pressure switch as a failsafe

Known issues & field notes

Mixing very old contact-only machines with Modbus machines needs an interface module per legacy unit

Operator and administrator levels set at commissioning by the Quincy distributor.

Manuals & literature

Quincy Compressor — manuals index

Public literature library

Direct PDFs

Browse all OEM manual portals →

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