Cooling
Re: Low Suction Pressure
A heat pump or air conditioner runs with a lower-than-normal suction pressure.
NORMAL SUCTION PRESSURE:
- R-22 = 55 - 80 psig
- R410a = 100 - 150 psig
| Qty |
Possible Causes: |
|
Low Refrigerant Charge |
|
Bad Expansion Valve |
|
Low/No Airflow |
|
Cold Outdoor Air |
|
Cold Return Air |
CHECKOUT:
Low Refrigerant Charge
- Low pressure due to low refrigerant charge will be accompanied by a warm suction line and a high superheat (see "Checking Superheat"). If the suction pressure is low and superheat is low (cold suction line) DO NOT ADD REFRIGERANT.
- If the suction pressure is low and the superheat is high try adding refrigerant. If the pressure does not come up and the superheat does not go down, suspect a bad metering device (below).
Bad Metering Device
- A bad metering device will typically result in a low suction pressure and a high superheat.
- If you have a low suction pressure and high superheat and suspect a bad metering device, try adding refrigerant to see if the suction pressure increases and the superheat decreases.
- If pressures and temperatures improve, the metering device is functioning properly.
- If the head pressure increases but the suction pressure stays the same or drops, the metering device is bad.
Low Airflow
- Low pressure caused by low airflow will be accompanied by a low superheat.
- Indoor airflow will affect the suction pressure in the cooling mode.
- Outdoor airflow will affect the suction pressure in heating mode.
Cold Ambient Temperature
- Cooling
- In the cooling mode, running in outdoor temperatures below 55 degree without a "low ambient control' will cause symptoms very similar to low refrigerant.
- The cold outside air will cause the head pressure to drop which, in-turn, causes the suction pressure to drop.
- Try blocking part of the outdoor fan discharge to increase head pressure.
- Heating
- As the outdoor temperature drops, the suction pressure will also drop.
Cold Return Air Temperature (cooling)
- The minimum return air temperature for cooling is around 64 deg.
- The colder the return air temperature gets, the lower the suction pressure will go.