Hello,

I believe that's the pressure on the low side gauge (blue gauge). And in the 900 only the low side connection is provided beside the accumulator. If that is so then your system is overfilled. You must reduce the charge amount.

The ac system is clutch cycling orifice tube. It needs precise amount of R134a. Not more or less. The charge weight is 950gm or about 32oz. If unsure better to recover the charge and start from zero. Using pressure reading to determine charge amount is almost impossible as R134a pressure rise/fall according to ambient temp.

Overfilling leads to high system pressure so lack of cooling. Underfilling leads to short cooling episodes with rapid compressor cycling so lack of overall cooling also. Hence the importance of correct charge.

That being said you can measure pressure first thing in the morning when engine is still cold. Don't start the engine. Just connect the gauge and read the system pressure. There's an apporoximate relationship between R134a pressure and ambient temp in Fahrenheit. For example 80F ambient would give around 81psi and 90F ambient would give around 95psi. Refer to R134a pressure to ambient temp chart in refrigeration websites for more accurate values. But these don't give the amount of charge available (i.e. how many grams or oz) in the system or how much more to add/reduce. This is just gives the general idea whether the system is overfilled or underfilled.

Hope this helps,
Amarin.