Heat Pump: Cooling
Re: High Discharge Pressure / High Head Pressure
As the system runs in the cooling 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 400 psig
| Qty |
Possible Causes (From Most to Least Likely): |
|
Refrigerant Overcharge |
|
Dirty Outdoor Coil |
|
Bad Condenser Motor |
|
Bad Fan Capacitor |
|
Mis-Sized Fan Blade |
|
Bad I/D Expansion Valve |
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 outdoor coil & indoor 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 Condenser Fan 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/Normal Suction Pressure = Overcharged
- Sub-Cooling > 13 deg. + High Discharge Pressure + Low Suction Pressure = Bad Expansion Valve
- Sub-Cooling < 2 deg. + High Discharge Pressure + Hot Liquid Line = Dirty Outdoor Coil or Mis-Sized Fan Blade --> Clean the coil and re-check.
3. Check Condenser Motor & Capacitor
- Disconnect power to the outdoor unit by pulling the service disconnect.
- Test the fan capacitor.
- Replace the capacitor if less than 20% of rated capacity.
- Re-apply power and check the fan motor amperage.
- Observe the motor operation and check for unusual noises (bad bearings) or excessive temperature.