Rheem/Ruud Heat Pump: RPNE/UPNE

Re: Low Pressure Lockout - HEATING

Units with model numbers ending in "JAZ" have an advanced defrost control with separate Low and High Pressure inputs and two diagnostic LED's.

A Low Pressure Lockout is indicated by the following LED pattern on the defrost board: LED 1 = ON, LED 2 = Flashing

The Low Pressure Control is an auto-reset type that opens at approximately 7 psig and closes at approximately 22 psig.

HEATING LOCKOUT: If the Low Pressure control opens 3 times within 120 minutes during a single call for heating, the defrost control will enter a Hard Lockout.  If the lockout occurs at an outdoor temperature below 5 deg F, the control will automatically reset once the outdoor temperature raises above 5 deg F (this is in case the low pressure fault was caused by excessively low temperatures).

LOCKOUT RESET:

• Cycle Low Voltage Power to the Defrost Control
• Short the two TEST pins

CHECKOUT:

1. Check Low Pressure Switch

• At the defrost board, check for 24VAC between each "LO-PS" terminal and "C".
  • Power on Both Terminals = Switch Closed → Step 2. Check Pressures
  • Power on One Terminal Only = Switch Open ⇒ Connect Refrigerant Gauges and check standing pressures.
    • Low Standing Pressure (less than 30psig) = Loss of Refrigerant / Low Refrigerant Charge
    • High Standing Pressure + Open Low Pressure Control = Bad Low Pressure Switch or Broken Wire

2. Check Refrigerant Pressures

• Hook-up refrigerant gauges to the pressure ports on the unit.
• Reset the unit if necessary.
• Allow the unit to run for 5-10 minutes.
• Monitor pressures as the system operates.
  • Normal R410a Suction Pressure = 100 - 150 psig
  • Normal R22 Suction Pressure = 35 - 65 psig

3. Check Superheat and Sub-Cooling

• Superheat
• Check the Suction Line Temperature near the compressor.
• 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 + High Sub-Cooling = Bad O/D Expansion Valve
• Low Suction Pressure + Low Superheat + High Sub-Cooling = Low Outdoor Heat Transfer (Frozen Outdoor Coil)
• Low Suction Pressure + High Superheat + Low Sub-Cooling = Low Refrigerant Charge