Rheem/Ruud Heat Pump: RPNE/UPNE

Re: Low Pressure Lockout - COOLING

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.

COOLING LOCKOUT: If the Low Pressure control opens 3 times during a single call for cooling, the defrost control will enter a Hard Lockout.

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 = 60 - 80 psig

3. 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 + High Sub-Cooling = Bad Expansion Valve
• Low Suction Pressure + Low Superheat + High Sub-Cooling = Low Indoor Heat Transfer
• Low Suction Pressure + High Superheat + Low Sub-Cooling = Low Refrigerant Charge or Low Outdoor Air Temperature

4. Check Indoor Temperature Drop

• Check the Return Air Temperature at the air handler or furnace.
  • Return Air Temperature below 64 deg. will cause low pressure issues.
• Check the Supply Air Temperature
  • Temperature Drop = Return Air Temperature - Supply Air Temperature
    • Normal Temperature Drop = 15 - 20 deg.
      • Low Temperature Drop = Bad Expansion Valve or Low Refrigerant Charge
      • High Temperature Drop = Low Heat Transfer