York YK Fault Code E21

E21
VSD output phase loss
Critical
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

York YK Fault Code E21 is a critical safety alarm indicating: VSD output phase loss. The most common causes include Output terminal loose. Estimated repair time: 30-60 minutes (requires electrical power diagnostics at disconnect). This alarm requires immediate attention by a certified HVAC technician.

Alarm Description

VSD output phase loss

Brand: York  |  Model: YK (Centrifugal Chiller (Water-Cooled))  |  Code: E21  |  Severity: Critical

Observable Symptoms

  • Phase monitor relay indicates phase loss or reversal
  • Compressor may run backwards or fail to start
  • Three-phase voltage readings are unbalanced

What to Check First

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

Quick Start: Check output voltage all phases

Probable Causes

  • Output terminal loose
  • Power module failure
  • Output cable damaged

Recommended Inspection Steps

  1. Check output voltage all phases
  2. Inspect terminals
  3. Verify power module

Required Tools & Equipment

  • Digital multimeter
  • Safety PPE (gloves, safety glasses, face shield)
  • Wire tracing and continuity tester

Estimated Repair Time

30-60 minutes (requires electrical power diagnostics at disconnect)

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 York service representative for warranty-covered repairs

Related Fault Codes

Other York YK codes that may be related:

E1E2E3E4E5

OEM Service Manual Reference

OEM Reference: York YK Centrifugal Chiller Service Manual (Form 160.60-S1). Johnson Controls Technical Literature.

Frequently Asked Questions

What does York YK fault code E21 mean?

Fault code E21 on a York YK chiller indicates: VSD output phase loss. This is a critical safety alarm that requires diagnostic attention.

What causes York YK alarm code E21?

Common causes include: Output terminal loose; Power module failure; Output cable damaged

How do I fix York YK error code E21?

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 York 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 York YK service procedures.