What does PRES FAULT mean on a Quincy QSI compressor?
Short answer: Pressure transducer faulty. If your Quincy QSI series (QSI standard controls) is showing PRES FAULT, the controller has logged a specific, documented condition. This page covers what it means, what causes it, what you can safely fix yourself, and when — and why — it takes a technician.
What exactly is the machine telling you?
The pressure transducer is faulty — either an open circuit or shorted — so the controller has lost its pressure signal.
Which machines show this?
Quincy QSI industrial rotary screw compressors with the standard QSI control panel — larger plant-air packages, some fitted with Quincy's integrated refrigerated dryer, whose faults (DRYER CONT., DRYER D.P.) appear on the same display without stopping the compressor. The QSI panel reports faults as short text messages — OVERLOAD, HIGH TEMP, SUMP HAT, TEMP FAULT — rather than numeric codes, so search the exact wording on your display. "Sump" in these messages means the fluid separator vessel, and "fluid" is Quincy's term for the compressor lubricant. Faults clear from the panel after the cause is corrected; the manual keeps the electrical enclosure strictly off-limits to unqualified hands.
What causes it?
- Pressure transducer failed open or shorted
- Control wiring fault between transducer and controller
- A transient signal loss that one power cycle may clear
Can you fix it yourself?
Power-cycle once; if the pressure signal doesn't come back, stop restarting. The controller is flying blind on pressure and shouldn't be forced to run.
Step by step — what to try, in order:
- Note the message and the last pressure reading
- Power-cycle the unit once to see if the signal returns
- Do not keep restarting the machine if the fault persists
When do you need a technician — and why?
Testing and replacing the transducer touches both the pressurized air circuit and the control wiring — a combined pressure-system and electrical job.
If it does come to a service call and you're in Nashville, TN or Birmingham, AL, we maintain independently compiled lists of local companies that service industrial air compressors — real businesses with verified contact information, none of whom paid to be listed.
Related questions
What does PRES FAULT mean on a Quincy QSI series (QSI standard controls)?
Pressure transducer faulty. The pressure transducer is faulty — either an open circuit or shorted — so the controller has lost its pressure signal.
Can I fix PRES FAULT on a Quincy QSI series (QSI standard controls) myself?
Power-cycle once; if the pressure signal doesn't come back, stop restarting. The controller is flying blind on pressure and shouldn't be forced to run.
When does PRES FAULT on a Quincy QSI series (QSI standard controls) need a technician?
Testing and replacing the transducer touches both the pressurized air circuit and the control wiring — a combined pressure-system and electrical job. Call a technician if the fault persists after one power cycle — transducer testing and replacement involves the pressurized air circuit and control wiring.
Verified against service documentation: Quincy QSI series (QSI standard controls) documentation for PRES FAULT (manualslib.com)