Climatemaster - Code 5 / LT2 Fault - Cooling

Article ID: 270
Last updated: 8 Feb, 2023

ClimateMaster Heat Pump: Cooling

Re: Code 5 / LT2 Fault

Code 5 = Low Air Coil Temperature (FP2)

  • The FP2 thermistor temperature must be below the selected low temperature limit setting (30 deg. unclipped) for 30 continuous seconds during a compressor run cycle to be recognized as a FP2 fault.
  • The FP2 input is bypassed for the initial 120 seconds of a compressor run cycle.
  • FP2 is set at the factory for one try. Therefore, the control will go into lockout mode once the FP2 fault has occurred.

Qty Possible Causes:
4 Low Refrigerant Charge
1 Expansion Valve Underfeeding
Bad FP2 Sensor
Low Air Flow (Filter or Coil)
Low Air Flow (Fan Speed)


1. Check Operating Conditions

  • Hook-up refrigerant gauges to the pressure ports in the unit.
    • Blue ⇔ Low Pressure Port (typically the middle line of the reversing valve)
    • Red ⇔ High Pressure Port (on the compressor discharge line)
  • Place an insulated temperature probe on the liquid line between the indoor coil and expansion valve.
  • Unplug the HWG pump motor (if the HWG piping is hooked-up and active).
  • If the heat pump is in lockout, reset by removing 24VAC power to the control board.
    • It can take up to 10 minutes for the heat pump to restart.
  • Set the thermostat to call for cool and ensure that the unit is running at full capacity (Y1 & Y2 Energized).
  • Allow the unit to run for at least 5 minutes.
  • Check and record the Water Pressure Drop through the geothermal unit.
  • Check and record the Entering Water Temperature and the Leaving Water Temperature.
  • Check and record Refrigerant Pressures.
  • Check & Record Sub-Cooling.
    • Sub-Cooling = Saturation Temp (from gauge) - Liquid Line Temp
  • Check and record the Air Temperature Drop through the unit.

► Be sure to re-connect the HWG pump before closing the unit.

2. Compare to Unit Performance Chart

  • Use Flow Sheet to convert pressure drop to GPM and then GPM per Ton.
  • Compare actual conditions to Unit Performance Chart.
    • Low Suction Pressure + High Sub-Cooling + Low Air Temp Drop = Under-Feeding Expansion Valve
    • Low Suction Pressure + Low Sub-Cooling + Low Air Temp Drop = Low Refrigerant Charge
    • Low Suction Pressure + Normal Sub-Cooling + High Air Temp Drop = Low Air Flow

3. Check FP2 Sensor

  • Turn off power to the unit.
  • Unplug the FP2 sensor (Violet) from the CXM board.
  • Check the resistance of the sensor & compare to Sensor/Resistance Chart (standard 10K ohm sensor)
  • Compare sensed temperature to actual temperature.
    • More than 5 deg. difference = Bad FP2 Sensor
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Article ID: 270
Last updated: 8 Feb, 2023
Revision: 24
Access: Public
Views: 8746
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