York Package Heat Pumps: BHZ

Re: Compressor not Running / Unit Locked-Out

• There are two control boards in this unit, a fan timer board and a defrost board.
• On the BHZ package units the defrost board controls the compressor contactor and condenser fan.

Safeties:

There is a high pressure switch and a low pressure switch wired in series to the "Pressure Switch" terminals on the defrost board.

• Hi Pressure Switch = 625 psig Cutout
• Lo Pressure Switch = 7 psig Cutout

Either switch opening with a call for "Y" will cause the heat pump to enter a "lockout".

► There is no LED on the board to indicate a lockout status.

CHECKOUT:

1. Check Power

• Disconnect power to O/D unit by pulling disconnect or turning off breaker.
  • Open the blower door and lower the electrical compartment cover. 
  • Use a multi-meter to check resistance across each fuse.
  • Inspect for burnt wiring or burnt contactor contacts.
• Re-apply power to the unit and set the thermostat to call for heat.
• Check for 24VAC between "R" and "C" on the Fan Timer control board.
  • No Power = No High Voltage Power, Blown Low Voltage Fuse or Bad Transformer
• Check for 24VAC between "Y" and "C" on the Fan Timer control board.
  • No Power = No Call from Thermostat ⇒ Check Thermostat
  • Power --> Compressor and Condenser Fan should start with 5 minutes.
    • No Compressor or Condenser Fan Operation after 5 minutes → Step 3. Check Safety Circuit

2. Check Operation

• Ensure that the indoor blower is operating.
  • Power on "Y", "G" or "W" + No Blower = Bad Blower Motor
• Ensure that the compressor and outdoor fan motor start properly.
  • Compressor Running + No Outdoor Fan = Defrost Mode, Bad Fan Motor or Bad Defrost Control Board
    • Ensure unit is not in defrost mode.
    • Check for 230VAC between the condenser motor "Common" wire (Black) at the defrost board and "Run" (Purple) wire at the capacitor.
      • Power + No Fan = Bad Cond Motor
      • No Power = Defrost Mode or Bad Defrost Control Board

3. Check Safety Circuit

• With wires plugged-in, check for 24VAC between "C" and both "Pressure Switch" terminals of the defrost control board.
  • Power on both terminals = Control likely in Lockout ⇒ Reset power and retry
  • Power on one terminal but not the other = Open Hi or Lo Pressure Switch → Step 4. Check Refrigerant Pressures

4. Check Refrigerant Pressures

• Hook-up refrigerant gauges to the pressure ports on the unit.
  • Very Low Pressures = Loss of Charge ⇒ Check for a leak
• Allow the system to run for at least 10 minutes.
• Monitor pressures as the system operates.

• Low Pressure Issues
  • Low Suction + Low Discharge + Expansion Valve Frosting = Low Refrigerant Charge
    • Try adding refrigerant through the Low Pressure gauge.
      • Suction and Discharge Pressures should gradually increase as refrigerant is added.
      • If the Discharge Pressure increases but the Suction stays low or drops = Bad Expansion Valve (See "Expansion Valve Issues" in Related Articles)
• High Pressure Issues
  • Place an insulated temperature probe on the liquid line between the evaporator coil & O/D expansion valve.
  • Allow the unit to run for at least 10 minutes.
  • Monitor pressures and temperature as the system operates.
    • If pressure exceeds Normal Range or kicks-off on Hi Pressure safety in the first 5 minutes = Refrigerant Overcharge or No Indoor Blower
  • Check Sub-Cooling
    • Record "Saturation Temperature" from the discharge pressure gauge.
    • Subtract the Actual liquid line temperature reading.
      • Saturation Temp - Liquid Line Temp = Sub-Cooling
        • Sub-Cooling > 13 deg. + High Discharge + High Suction = Overcharged
        • Sub-Cooling > 13 deg. + High Discharge + Low Suction = Bad Expansion Valve
        • Sub-Cooling < 2 deg. + High Discharge = Low Indoor Heat Transfer

5. Check Defrost

• Cycle the heat pump through a defrost by shorting the TEST pins on the defrost board.
• Observe refrigerant pressures.
• Unit should terminate defrost somewhere around the following pressures:
  • 125 - 140 Suction 
  • 300 to 400 Discharge.