Scroll Chillers Critical Interlock

Daikin McQuay AGZ Chiller Alarm E1: Evaporator Flow Loss

Published: 2026-04-03

🚨 Critical Diagnostic Alert

Alarm E1 on the Daikin McQuay AGZ air-cooled scroll chiller indicates that the MicroTech III controller has detected a loss of chilled water flow through the evaporator. This is a safety-critical alarm — operating a brazed plate evaporator without water flow will freeze the heat exchanger within 60-90 seconds (the water inside the BPHE turns to ice, expands, and cracks the stainless steel plates).

The MicroTech uses a two-stage flow verification: 1) The pump auxiliary contact must prove the pump starter has energized (electrical proof), AND 2) The differential pressure flow switch must prove actual flow (mechanical proof). Both must be satisfied within 30 seconds of the pump start command. Understanding this two-stage logic prevents misdiagnosis — an E1 can be an electrical problem (failed aux contact), a mechanical problem (failed flow switch), or an actual flow problem (failed pump, closed valve, clogged strainer).

🔍 Symptoms Checklist

⚠️ MicroTech controller displays 'E1 — Evap Flow Loss'
⚠️ Entire chiller shuts down (not just one circuit)
⚠️ Alarm triggers within 30 seconds of chiller start command
⚠️ Chilled water pump may be running but not proving flow

🛠️ OEM Replacement Parts

Part Name	OEM Part Number	Est. Price
Differential Pressure Flow Switch (Field-Adjustable)	`DKN-FLOW-SW`	$225
Chilled Water Pump Contactor (with Aux Contact)	`DKN-PUMP-CONT`	$165
MicroTech III Controller Flow Input Module	`DKN-MT3-FLOW`	$580

📋 Interactive Diagnostic Procedure

Click each step to expand detailed diagnostic instructions. Follow in sequence — each step builds on the previous one.

1 Verify Flow Switch Actuation & Setting

The AGZ uses a differential pressure (paddle-less) flow switch that senses pressure drop across the evaporator. This switch must be field-adjusted during commissioning. Measure the actual evaporator pressure drop with a differential pressure gauge. Compare against the flow switch's trip point (adjusted via the set screw on the switch body). If the switch is set too high — e.g., requiring 12 PSID when the actual operating delta-P at design flow is 10 PSID — the chiller will trip on 'flow loss' even with proper flow. Re-adjust per the commissioning procedure: reduce the switch setting until it trips, then increase by 20%.

2 Check Chilled Water Pump Starter/Contactor

The MicroTech controller commands the chilled water pump via a digital output to the pump starter. Verify the pump contactor is pulling in when the chiller receives a start command. Check the auxiliary contact on the pump starter that provides pump-running proof to the MicroTech — if this aux contact is not closing (due to a failed microswitch or loose wire), the MicroTech will declare flow loss even though the pump is running and flow is adequate.

3 Inspect Evaporator Strainer

AGZ chillers require a Y-strainer on the evaporator inlet to protect the brazed plate heat exchanger from debris. A clogged strainer reduces flow and increases pressure drop across the strainer — but not across the evaporator itself, which is where the flow switch measures. Key diagnostic: if the pump discharge pressure is high but evaporator delta-P is low, the restriction is upstream of the evaporator (strainer or isolation valve). Clean the strainer and re-check evaporator delta-P.

4 Test Flow Switch with Manual Simulation

To confirm whether the flow switch or the wiring/controller is at fault: disconnect the flow switch wires at the MicroTech input terminals. Jumper the input terminals closed (simulating flow proven). If the chiller starts and runs normally with the jumper in place, the flow switch itself is faulty or the evaporator flow is genuinely inadequate. If the chiller still trips on E1 with the input jumpered, the MicroTech input module is faulty — it's not recognizing the closed circuit. Replace the input module.

Frequently Asked Questions

Can I bypass the flow switch temporarily to keep the chiller running?

Absolutely not. The flow switch is the sole protection against a freeze event that would destroy the evaporator ($5,000-15,000 repair). Bypassing it for even 30 seconds of operation without verified water flow will crack the brazed plate heat exchanger. If you must run the chiller while waiting for a replacement flow switch, station a technician at the chiller to manually verify flow at the pressure gauges continuously.

🔗 Related Error Codes — Scroll Chillers

Other diagnostic guides in the same equipment category. Common failure patterns often share root causes — cross-referencing speeds up diagnosis.

Scroll Chillers Critical Interlock

⚡ Fault-Induced Energy Waste Estimator

When HVAC equipment runs with active error codes, it operates inefficiently and wastes electricity. Estimate the monthly cost of delaying repairs. All calculations run locally in your browser.

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References & Industry Standards

ASHRAE 15 — Safety Standard for Refrigeration Systems
ASHRAE 34 — Refrigerant Designation & Safety Classification
AHRI 550/590 — Water-Chilling & Heat Pump Packages
SMACNA — HVAC Duct Construction Standards
Manufacturer Service Manuals — Carrier, Trane, York, Daikin, Lennox

Daikin McQuay AGZ Chiller Alarm E1: Evaporator Flow Loss

🔍 Symptoms Checklist

🛠️ OEM Replacement Parts

📋 Interactive Diagnostic Procedure

Frequently Asked Questions

🔗 Related Error Codes — Scroll Chillers

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Trane CGAM Alarm HPC: High Pressure Cutout — Circuit Protective Trip

York YLAA Scroll Chiller Alarm B5: Phase Loss / Phase Reversal Protection

Daikin McQuay AGZ Alarm E3: Compressor Motor Overload — Thermal Trip

Carrier AquaSnap 30RAP Alarm 52: Circuit Defrost — Freeze Prevention Active

⚡ Fault-Induced Energy Waste Estimator

References & Industry Standards