YH2E - Code 5 - Low Pressure Fault - Heating

York Heat Pump: YH2E

Re: Low Suction Pressure - Code 5 (Heating)

CODE 5 = Low Pressure Switch Opened (2x in 6 hours)

CHECKOUT:

1. Check Refrigerant Pressures

• Pull the service disconnect.
• Make sure the outdoor coil is not frozen-over.
  • Frozen coil = Not Defrosting
• Hook-up refrigerant gauges to the pressure ports on the unit.
  • Blue ⇔ True Suction (Not Suction Line)
  • Red ⇔ Liquid Line Pressure Port
    • Low Standing Pressure (both sides) = Loss of Charge
    • Normal Pressures ⇒ Continue
• Start the unit.
  • Re-Insert the service disconnect.
  • Reset the lockout (if necessary) by removing and re-inserting the low voltage plug from the defrost board.
  • Bypass the Anti-Short-Cycle Delay by jumping the Test pins.
  • Allow the unit to run for 5-10 minutes.
  • Monitor pressures as the system operates.
    • Normal Pressure + Code 5 Again = Bad Pressure Switch
      • Normal R410a Suction Pressure = 100 - 150 psig

2. Check Suction Pressure & Sub-Cooling

• 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 Sub-Cooling (Clear Sight Glass) = Bad O/D Expansion Valve
• Low Suction Pressure + Low Sub-Cooling (Bubbles in Sight Glass) = Low Refrigerant Charge 

3. Check the Low Pressure Switch & Defrost Board

• If everything checks-out correctly in Steps 1 & 2, it may be necessary to temporarily bypass the low pressure switch.
  • If the unit operates properly with no Code 5 lockouts, assume a Bad Low Pressure Switch.
  • Unit still locks-out on Code 5 = Bad Defrost Board