YZF - High Discharge Temperature (Cooling)

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.

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.

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