Heat Pump: Heating

Re: High Discharge Pressure / High Head Pressure

As the system runs in the heating mode, the discharge pressure exceeds the normal operating pressure.

R22 System

• Normal Head Pressure = 175 - 250 psig
• High Head Pressure = Above 275 psig

R410A System

• Normal Head Pressure = 225 - 350 psig
• High Head Pressure = Above 450 psig

CHECKOUT:

1. Check Refrigerant Pressures

• Hook-up refrigerant gauges to the pressure ports on the unit.
  • Blue ⇔ "True Suction" Low Pressure
  • Red ⇔ High Pressure (either refrigerant line)
• 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 = Bad Overcharge or No Indoor Blower ⇒ Check Blower Motor Operation

2. 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 Pressure + High Suction Pressure = Overcharged
    • Sub-Cooling > 13 deg. + High Discharge Pressure + Low Suction Pressure = Bad Expansion Valve
    • Sub-Cooling < 2 deg. + High Discharge Pressure = Low Indoor Heat Transfer ⇒ Check Heat Pump Temperature Rise

3. Check Heat Pump Temperature Rise

• Check to make sure the indoor fan is operating.
• Disconnect auxiliary heat (remove "W" at the air handler or thermostat).
• Check the Return Air Temperature at the air handler (at the filter if possible).
  • High Return Air Temperature (more than 85 deg.) = Heat Recycling
• Check the Supply Air Temperature near the air handler (in a straight duct run if possible).
• Calculate the Temperature Rise = Supply Air Temperature - Return Air Temperature
  • Normal Heat Pump Temperature Rise = 15 - 20 deg.
    • High Temperature Rise = Low Airflow ⇒ Check Air Filter

4. Check Air Filter & Indoor Coil

• Remove the Air Filter and Check for a Dirty Indoor Coil
• If the Indoor Coil is OK ⇒ Re-Check Temperature Rise with the filter removed.
  • No Change = Restricted Ductwork or Low Blower Speed ⇒ Check Duct Static Pressure
  • Temperature Rise Becomes Normal = Clogged Air Filter ⇒ Replace Filter & Re-check Pressures

5. Check Duct Static Pressure

• Check the return static pressure (between the air handler and filter if possible).
• Check the supply static pressure.
  • High Static = Above 0.5" w.c.
    • High Return Static + Low Supply Static = Restricted Return Ductwork
    • Low Return Static + High Supply Static = Restricted Supply Ductwork
  • Static Pressure Normal ⇒ Increase Blower Speed or Clean Blower Wheel