DNH - Cooling - Indoor Coil Frozen

York Package Unit: DNH

Re: Cooling - Indoor Coil Frozen

The unit is operating in the cooling mode. The compressor and condenser fan motor are operating and the suction line to the compressor and indoor coil are frozen.

CHECKOUT:

1. Check System Operation

• At the thermostat, turn the System switch to "OFF" and turn the Fan Switch to "ON".
• Confirm that the outdoor fan and compressor stop operating.
  • Stays Running = Stuck Contactor
• Confirm that the indoor blower is operating.

2. Check Blower Wheel, Motor & Capacitor

► The 2 - 4 Ton Models use a standard, PSC Motor. The 5 Ton Model uses a Variable-Speed, ECM Motor

• Disconnect high voltage power to the unit.
• Manually turn the blower wheel to check wheel & motor bearings.
  • Wheel Loose or Wobbly on Shaft = Broken Blower Wheel
  • Motor Stiff or Won't Turn = Bad Blower Motor
• 2 - 4 Ton Models
• Check the blower motor capacitor.
  • Capacity Less than 80% of Rating = Bad Capacitor
• Re-Apply power to the unit.
• Energize a call for "Fan-Only".
  • Blower Motor Operates → Step 3. Thaw the Coil
  • Blower Motor Doesn't Run ⇒
    • Check for 24VAC across the coil of the blower relay/contactor.
      • No Power = No Call for "G" or Bad Control Board
    • Check for 230VAC from the Purple wire on L2 of the contactor to the motor speed wire on the leaving side of the fan relay/contactor.
      • 24V Power on Relay + No 230V = Bad Fan Relay
      • 230V + No Fan Operation = Bad Blower Motor
• 5 Ton Models
• Re-Apply power to the unit.
• Energize a call for "Fan-Only".
  • Blower Motor Operates → Step 3. Thaw the Coil
  • Blower Motor Doesn't Run ⇒
    • Check for 24VAC between "C" and the "Heat" terminal on the control board.
    • Check for 24VAC between "C" and the "Cool" terminal on the control board.
      • 24V Power on "Heat" or "Cool" + No Blower Operation = Bad Blower Motor
      • No Power on "Heat" or "Cool" = No Call for "G" or Bad Control Board

3. Thaw the Coil

• Make sure that the coil is completely thawed before restarting compressor & checking refrigerant charge.
• If the coil is not visible, a way to see if there is still ice on the coil is by checking the refrigerant "standing" pressure.
  • The evaporation/saturation temperature on the gauge will equal the return air temperature once the coil thaws.

4. Check Filter & Indoor Coil

5. Check Refrigerant

• Hook-up refrigerant gauges to the pressure ports sticking through the cabinet.
• Monitor pressure as the system operates.

• Normal Pressure Range
  Refrigerant	0-30 Deg O/D	30-50 Deg O/D
  R410A	75-100 Suction 250-320 Discharge	100-150 Suction 250-375 Discharge

• Low Pressure Issues
  • Low Suction + Low Discharge + Expansion Valve Frosting = Low Refrigerant Charge or Bad Expansion Valve
    • 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