Heat Pump - Low Heat

CHECKOUT:

1. Check Unit Status & Power

• Unit Status
• Inspect the outdoor unit and make sure the outdoor coil is not frozen-over = Defrost Problem
• Unit Operating --> Step 2. Check Compressor Operation
• Power
• Disconnect power to O/D unit by pulling disconnect or turning off breaker.
  • Open the electrical compartment cover. 
  • Inspect for burnt wiring or burnt contactor contacts.
• Re-apply power to the unit.
• Check for 200 - 240VAC power on the contactor inlet.
  • No Power = Tripped Breaker or Bad Wiring
• Check for 24VAC between "R" and "C" on the defrost control board.
  • No Power = Blown Low Voltage Fuse or Bad Transformer
• Set the Thermostat to call for heat.
  • Check for 24VAC between "Y" and "C" on the defrost control board.
    • No Power = No Call from the Thermostat ⇒ Check Thermostat
    • Power ⇒ Compressor and Condenser Fan should start within 5 minutes.

2. Check Compressor Operation

• Re-Apply Power to the unit (if turned off from the previous step).
  • Compressor and Condenser Fan start and run normally → Step 3. Check Refrigerant Pressures
  • Compressor Does Not Try to Start = Control in Lockout, Bad Control Board or Bad Contactor
    • Check for 24VAC between each "Pressure Switch" terminal and "C" on the defrost board.
      • Power on One Side Only = Open Hi or Lo Pressure Switch
      • Power on Both Sides = Pressure Safeties OK ⇒ Reset control by disconnecting "R" and "Y" from the board then re-check.
        • Short the "TEST" terminals on the defrost control to bypass the "Wait" timer.
        • Check for 24VAC across both contactor coil wires.
          • Power + Contactor Doesn't Pull-in = Bad Contactor
          • No Power ⇒ Suspect Bad Control Board
  • Compressor Hums but Doesn't Run = Bad Capacitor, Locked-up Compressor, or Burnt Compressor Wiring

3. Check Refrigerant Pressures

• Hook-up refrigerant gauges to the pressure ports on the unit.
  • Blue --> "True Suction" Port (Not Suction Line)
  • Red --> High Pressure (either refrigerant line)
• Monitor pressures as the system operates.

• If a Liquid-Line Sight Glass is installed, observe for bubbles in the sight glass (after the system has been operating for at least 5 min.)
  • Bubbles = Low Refrigerant Charge
• Low Pressure Issues
  • Low Suction Pressure + Clear Sight Glass + Expansion Valve Frosting = Bad Expansion Valve 
  • Low Suction Pressure + Low Discharge Pressure + Bubbles in Sight Glass + 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
• 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
      • Normal Sub-Cooling = 4 - 13 deg.
        • High Sub-Cooling + High Discharge Pressure + Normal or High Suction Pressure  = Overcharged
        • High Sub-Cooling + High Discharge Pressure + Low Suction Pressure = Bad Expansion Valve
        • Low Sub-Cooling + High Discharge Pressure = Low Indoor Heat Transfer → Step 5. Check Air Temperature Rise

4. Check Compressor Discharge Temperature

• Use a multi-meter to check the temperature of the compressor discharge line.
• Normal Temperature = 120 - 150 deg.
  • Low Discharge Temp = Inefficient Operation

5. Check Air Temperature Rise

• With the auxiliary heaters disconnected (remove "W1" and "W2" form the air handler terminal block):
  • Check the Return Air Temperature near the unit or in the filter compartment.
  • Check the Supply Air Temperature.
  • Normal Temperature Rise = 15-20 deg.
    • Abnormally Low Return Air Temperature ⇒ Check Return Ductwork for Cold Air Infiltration
    • Low Temperature Rise = Inefficient Operation
      • Be cautious of "Directional Heat Issue"
    • High Temperature Rise = Low Airflow
  • RE-HOOK "W1" AND "W2" WIRES ON THE AIR HANDLER!