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T133

T133 — Circuit A Low Refrigerant Pressure

Carrier · Energy Recovery Ventilators

What does T133 mean?

This indicates low refrigerant pressure in Circuit A. Several factors can contribute to this condition.

Common Causes

  • Low refrigerant charge
  • Dirty filters
  • Evaporator fan is rotating backward
  • Loose or broken fan belt
  • Plugged filter drier
  • Faulty transducer
  • Excessively cold return air
  • Stuck open economizer at low ambient temperature

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    Check and clean or replace filters.

  2. 2

    Verify the evaporator fan is rotating correctly and the belt is tensioned.

  3. 3

    Inspect the filter drier for blockage.

  4. 4

    Check the relevant transducer for proper operation.

  5. 5

    Ensure the economizer is not stuck open in low ambient temperatures.

  6. 6

    Consult a qualified technician for refrigerant service.

Browse all codes in this manual (60)
Verified technical data. Last updated: April 2026

Related Faults

1 Fault CodeFault Code 1 — OVERCURRENT10 Fault CodeFault Code 10 — PANEL LOSS11 Fault Code11 Fault Code — ID RUN FAIL
Source: Carrier Energy Recovery Ventilators
Open Manual (Page 47)Search more codes in this manual