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YZF - High Discharge Temperature (Cooling)

Article ID: 334
Last updated: 15 Dec, 2020

York Heat Pump: YZF

Re: High Discharge Temperature Fault (Cooling)

A High Temperature Lockout is indicated by the following LED pattern on the outdoor unit control board:

  • Green = 5 Flashes
  • Red = On

X/L Output

  • 2 Flashes at Thermostat = Soft Lockout
    • Switch opened two times in 6 hours.
    • Reset by cycling thermostat or jumping Test pins.
  • 3 Flashes at Thermostat = Hard Lockout
    • Four Soft Lockouts in 12 hours.
    • Reset by cycling 24VAC power to the board.

Qty Possible Causes:
1 Low Refrigerant
Bad I/D Expansion Valve
Refrigerant Over-Charge
Bad Discharge Sensor

CHECKOUT:

1. Check Refrigerant Pressures

  • Hook-up refrigerant gauges to the pressure ports on the unit.
  • Allow the unit to run for 5-10 minutes.
  • Monitor pressures and temperature as the system operates.
Normal Pressure Range
Refrigerant 55-75 Deg O/D 75-95 Deg O/D
R410A
  • 110 - 130 Suction
  • 225 - 300 Discharge
  • 125 - 150 Suction
  • 250 - 375 Discharge


2. Check Superheat and Sub-Cooling

  • Superheat
  • Check the Suction Line Temperature near the outdoor unit.
  • Record the "Evaporation Temperature" from the Suction pressure gauge.
    • Superheat = Suction Line Temperature - Evaporation Temperature
      • Normal Superheat = 8 - 18 deg.
  • Sub-Cooling
  • Check the Liquid Line Temperature near the outdoor unit.
  • Record "Saturation Temperature" from the discharge pressure gauge.
    • Sub-Cooling = Saturation Temp - Liquid Line Temp
      • Normal Sub-Cooling = 3 - 12 deg. (Sight-Glass Clear)
  • Low Suction Pressure + High Superheat + Low Sub-Cooling (Bubbles in Sight-Glass) = Low Refrigerant Charge or Low Outdoor Air Temperature
  • Normal Suction Pressure + Normal Superheat + High Head Pressure + High Sub-Cooling (Clear Sight-Glass) = Refrigerant Over-Charge
  • Low Suction Pressure + High Superheat + High Sub-Cooling (Clear Sight-Glass) = Bad I/D Expansion Valve
    • Examine I/D Expansion Valve: An under-feeding valve should be frosting at the valve.

3. Check Discharge Temperature

  • Connect a temperature thermistor to the compressor discharge line near the discharge sensor.
  • Allow the system to run for about 10 minutes and watch the actual discharge temperature.
    • Normal Discharge Temperature = 130 - 180 deg F.
    • Trip Point = 250 deg. F.

4. Check Discharge Sensor

  • Disconnect power to the outdoor unit by pulling the disconnect or turning the breaker off.
  • Remove 24V power from the Yorkguard board by removing the "R" wire.
  • Unplug the discharge sensor from the Yorkguard board.
  • Use the York Resistance Chart to check the temperature of the sensor.
    • Sensor Temperature 10 deg. higher or lower than the Actual Temperature = Bad Discharge Sensor

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Article ID: 334
Last updated: 15 Dec, 2020
Revision: 10
Views: 73
Comments: 0
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