The question comes up all the time of what we should be seeing for pressures on a minisplit system. Weather its Fujitsu, Daikin, Comfortaire, Mitsu... etc They all basically operate and aim for the same target pressures and temperatures.

 

Two ways this is normally talked about:

• Standing Pressure Reading- I am not a fan of this because its not a totally accurate way of doing it. Standing pressure is when there is no pumping differential or metering that is happening. So your standing pressure will usually match up to where the refrigerant is coldest in the system. This could be inside or outside. For the most part if you are below 100 psi (30-35 degrees) in the summer you are probably low, as there should not be a place that cold where the minisplit components are in. Again, I DO NOT suggest this at all.
• Test Run- The way we should do it is putting the unit into test mode. Set unit for 64 degrees and high fan, then put in to test mode. This bypasses the thermistor on the indoor unit and allows the unit to run without slowing down. We should see pressures between 110-133 PSI (37-43 Degree) Evaporator Pressure/Temperature. Remember, these are "comfort cooling" units and they should target like any other unitary system. So do not over complicate it.  In heating mode, you would take the same approach except put the unit on high fan and 88 degrees. You will want to see reading of 390-430 PSI (108-130 degrees). If you are below that you are probably undercharged. 

 

 

Tech Tip: Checking Pressure Readings on Fujitsu Mini-Splits

When diagnosing refrigerant charge issues on a Fujitsu mini-split (or similar systems like Daikin, Mitsubishi, or Comfortaire), follow these key points for accurate readings:

 

⚠️ Standing Pressure Reading (NOT Recommended)

Measures system pressure when idle (no pumping or metering).

 

Often unreliable because pressure aligns with the coldest point in the system.

 

Rule of Thumb: Below 100 PSI (30-35°F) in summer suggests a possible low charge.

 

Why Avoid It: Standing pressure can vary significantly and mislead diagnosis.

 

✅ Test Run Method (Recommended)

For accurate pressure readings, use the Test Mode feature:

 

Cooling Mode:

 

Set unit to 64°F with fan on high.

 

Activate Test Mode to bypass the indoor thermistor and run the system at full output.

 

Target Pressure: 110-133 PSI (37-43°F evaporator pressure/temperature).

 

Heating Mode:

 

Set unit to 88°F with fan on high.

 

Target Pressure: 390-430 PSI (108-130°F condenser pressure/temperature).

 

🔍 Key Tips for Accurate Testing

Always check for clean coils and proper airflow before diagnosing pressure issues.

 

Ensure refrigerant lines are free of kinks or restrictions.

 

Low pressures in test mode often indicate undercharge or leakage.

 

If pressures fluctuate dramatically, consider potential sensor or valve issues.

 

💡 Pro Tip:

Mini-splits are designed for comfort cooling, similar to traditional unitary systems — so keep diagnostics simple and methodical.