Commercial Rooftop Units Critical Interlock

York Predator RTU Alarm 3H: Compressor Thermal Overload Trip

Published: 2026-04-16

🚨 Critical Diagnostic Alert

Alarm 3H on York Predator commercial rooftop units indicates that the compressor's internal thermal overload protector has tripped — the motor winding temperature exceeded the safe limit (typically 185-200°F internal). This is a protective trip, not a compressor failure. The compressor is thermally protecting itself from damage.

The key diagnostic clue: if the alarm only triggers after 4+ hours of continuous operation and the unit cools normally after a 2-hour cooldown, the compressor motor itself is likely fine — the problem is a system condition causing it to run hot (poor motor cooling, high compression ratio, or electrical supply issues). If the alarm triggers within 30 minutes of startup, suspect a failing compressor (shorted turns) or a severe electrical issue.

🔍 Symptoms Checklist

⚠️ Compressor contactor is energized but compressor not running
⚠️ Compressor housing extremely hot to touch (>180°F)
⚠️ Alarm triggers only after 4-6 hours of continuous operation
⚠️ Unit cools normally for several hours before tripping

🛠️ OEM Replacement Parts

Part Name	OEM Part Number	Est. Price
Compressor Thermal Overload Module	`YK-025-39012-000`	$175
Compressor Contactor (3-Pole, 40A)	`YK-C40-3P`	$120
Crankcase Heater (70W, 230V)	`YK-CCH070`	$65

📋 Interactive Diagnostic Procedure

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

1 Measure Compressor Winding Resistance

After the compressor has cooled to ambient temperature (minimum 2 hours with power off), disconnect the compressor leads at the contactor. Measure winding resistance: Common-to-Start, Common-to-Run, and Start-to-Run. All three should be within 10% of each other. A reading of 0Ω indicates a shorted winding. A reading of infinite Ω indicates an open internal overload (which should reset after cooling) — if it doesn't reset after 2+ hours of cooling, the internal thermal protector has failed permanently.

2 Check Compressor Contactor Condition

A pitted or burned contactor creates high resistance at the contact points, causing voltage drop that increases compressor current draw. Remove the contactor cover and inspect the contacts: pitting, discoloration (blue/brown = overheating), or excessive carbon tracking indicate replacement is needed. Measure voltage drop across each closed contact while the compressor is running — any drop >1% of line voltage (e.g., >2.3V on a 230V circuit) indicates contact degradation.

3 Verify Crankcase Heater Operation

The crankcase heater prevents liquid refrigerant from migrating to the compressor sump during off-cycles. A failed crankcase heater allows liquid refrigerant to accumulate in the oil, causing flooded starts that overheat the motor windings. Measure the heater resistance (should read ~750Ω for a 70W heater) and verify it's receiving continuous power during the off-cycle. A cold compressor sump after an 8-hour off-cycle confirms heater failure.

4 Check Superheat at Compressor Suction

Inadequate suction superheat (<10°F at the compressor) allows liquid refrigerant droplets to enter the compressor, reducing motor cooling and triggering the thermal overload. This is a system-level problem, not a compressor problem. Check: TXH sensing bulb mounting (must be tight, insulated, on a horizontal pipe run at 4 or 8 o'clock position), evaporator airflow (low airflow → low superheat), and refrigerant charge (overcharge → high head pressure → reduced compressor cooling).

🔗 Related Error Codes — Commercial Rooftop Units

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

Commercial Rooftop Units Warning (Reduced Capacity)

⚡ 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.

Unit Power Consumption (kW)

Extra Run Time Due to Fault (Hours/Day)

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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

York Predator RTU Alarm 3H: Compressor Thermal Overload Trip

🔍 Symptoms Checklist

🛠️ OEM Replacement Parts

📋 Interactive Diagnostic Procedure

🔗 Related Error Codes — Commercial Rooftop Units

Trane RTU Error ERR04: Evaporator Frost Protection Active

Carrier WeatherExpert RTU Alarm A001: Supply Air Temperature Sensor Failure

Lennox Energence RTU Alarm 27: High Pressure Cutout — Condenser Fan Failure

Carrier WeatherExpert RTU Alarm A002: Return Air Temperature Sensor Failure

Trane RTU Error ERR07: High Compressor Discharge Temperature —...

Lennox Energence RTU Alarm 31: Low Suction Pressure — Refrigerant...

York Predator RTU Alarm 4A: Condenser Fan VFD Fault — Variable Speed

Carrier WeatherExpert RTU Alarm A005: Economizer Actuator Feedback Error

⚡ Fault-Induced Energy Waste Estimator

References & Industry Standards