McQuay ALS Fault Code E27

E27
Chiller staging error
Warning
SAFETY WARNING: Commercial chillers contain high-pressure refrigerants and high-voltage electrical components (208V-4160V). Only EPA Section 608 certified technicians should perform diagnostic work. Always follow lockout/tagout procedures and wear appropriate PPE. Do not attempt repairs without proper training and equipment.
AI Summary

McQuay ALS Fault Code E27 is a warning alarm indicating: Chiller staging error. The most common causes include Staging logic error. Estimated repair time: 1-2 hours. This alarm requires immediate attention by a certified HVAC technician.

Alarm Description

Chiller staging error

Brand: McQuay  |  Model: ALS (Air-Cooled Screw Chiller)  |  Code: E27  |  Severity: Warning

Observable Symptoms

  • Controller displays alarm code and description
  • Chiller may be locked out or running in degraded mode
  • Alarm indicator light is illuminated on control panel

What to Check First

Before diving into detailed diagnostics, start with this quick first check:

Quick Start: Check staging config

Probable Causes

  • Staging logic error
  • Capacity mismatch
  • Lead/lag fault

Recommended Inspection Steps

  1. Check staging config
  2. Verify settings
  3. Reset logic
  4. Check signals

Required Tools & Equipment

  • Digital multimeter
  • OEM service manual
  • Safety PPE (gloves, safety glasses)
  • Safety PPE (gloves, safety glasses, face shield)

Estimated Repair Time

1-2 hours

When to Call a Professional

  • If the fault persists after completing all recommended inspection steps
  • If you observe unusual noises, vibrations, or oil leaks from the compressor
  • If refrigerant charge levels are outside OEM specifications and EPA-certified recovery is needed
  • If electrical measurements show voltage imbalance greater than 2% between phases
  • If the fault recurs immediately after reset, indicating an unresolved safety condition
  • Contact an authorized McQuay service representative for warranty-covered repairs

Related Fault Codes

Other McQuay ALS codes that may be related:

E01E02E03E04E05

OEM Service Manual Reference

OEM Reference: McQuay ALS Air-Cooled Screw Chiller Service Manual. Available through Daikin Applied technical support.

Frequently Asked Questions

What does McQuay ALS fault code E27 mean?

Fault code E27 on a McQuay ALS chiller indicates: Chiller staging error. This is a warning alarm that requires diagnostic attention.

What causes McQuay ALS alarm code E27?

Common causes include: Staging logic error; Capacity mismatch; Lead/lag fault

How do I fix McQuay ALS error code E27?

Follow the recommended inspection steps below. Start with the quick check, then proceed through each step. If the fault persists after all steps, contact an authorized McQuay service representative.

Disclaimer: All lookup data is for reference only. Do not use this information to replace certified professional HVAC technician judgment. Always refer to original OEM official service manual for McQuay ALS service procedures.