Heatcraft Refrigeration Alarm 3 — High Discharge Temperature

Heatcraft Refrigeration Alarm 3 — What It Means

On Heatcraft condensing units and remote condensers (Larkin, Bohn, Climate Control, and Chandler brands under the Heatcraft umbrella), Alarm 3 indicates the discharge temperature sensor has detected compressor discharge gas temperature above the safe limit — typically 240–260°F (115–127°C) depending on the unit and refrigerant type. High discharge temperatures cause oil breakdown, valve carbonization, and accelerated compressor wear. The unit shuts down on Alarm 3 to prevent compressor damage. It will not restart until the temperature drops below the reset threshold.

Jump to Fix

Common Causes

• Low refrigerant charge (leak) — Insufficient refrigerant causes the compressor to run at high pressure differential with low suction density, compressing a smaller mass of gas more aggressively. The result is abnormally high discharge temperatures. This is the most common cause.
• Dirty or fouled condenser coil — A coil blocked by dirt, cottonwood seeds, or grease (in kitchen environments) cannot reject heat effectively. Condensing pressure rises, discharge temperature follows.
• Failed condenser fan motor or blade — One or more condenser fans not running allows condensing pressure and discharge temperature to climb, especially in warm weather.
• High superheat at the evaporator — Excessive superheat entering the compressor (from a misadjusted or failing TXV, or low refrigerant) means the suction gas is already hot before compression begins, pushing discharge temp higher.
• Refrigerant restriction (filter drier or metering device) — A saturated filter drier or a stuck closed expansion valve starves the evaporator of refrigerant, creating the same low-charge symptom profile including high discharge temp.

Step-by-Step Fix {#fix}

1. Check condenser fans first — With the unit running, verify all condenser fans are operating and drawing air across the coil. A stopped fan is the easiest and cheapest fix. Check capacitors on single-phase fan motors.
2. Inspect and clean the condenser coil — Examine the coil surface for dirt, debris, or grease buildup. Clean from the inside out using a coil cleaner appropriate for the environment (food-safe cleaner near food equipment).
3. Connect refrigerant gauges — Measure suction and discharge pressures. Compare to the pressure-temperature (PT) chart for the refrigerant type (R-22, R-404A, R-448A, etc.). Low suction pressure with high discharge pressure and high discharge temperature is the classic low-charge signature.
4. Check superheat — Measure suction line temperature at the evaporator outlet and suction saturation temperature from the suction gauge. The difference is superheat. Values above 20°F suggest the TXV is starving the evaporator (restriction, misadjustment, or low charge).
5. Inspect the filter drier — A cold or frosted filter drier indicates restriction (pressure drop across it). Replace it — a saturated drier is also contaminating the refrigerant circuit with moisture.
6. Check for refrigerant leak — If charge is low, find and repair the leak before adding refrigerant. Adding refrigerant to a leaking system is a short-term fix and wastes refrigerant.
7. Reset the alarm and restart — After repairs, allow the discharge temperature to drop below the reset threshold (usually 200°F/93°C), then reset Alarm 3 from the Heatcraft controller panel. Monitor discharge temperature during the first operating hour.

Parts Often Needed

When to Call a Pro

All refrigerant work (leak detection, recovery, and recharge) requires EPA 608 certification. High-side refrigerant pressures on commercial refrigeration equipment can exceed 400 PSI — proper manifold gauge sets and safety procedures are essential. Heatcraft’s technical support line (1-800-922-1919) can assist with unit-specific fault codes and pressure-temperature charts.