If you could hook up one of those refill can of refrigerant with the gauge you can see what type of pressure you have in the system. I think that your system pressure is low thus activating the low pressure switch to prevent the compressor clutch from energizing. If the system pressure is below 1.5 bars the switch will be activated. You will connect the refill can to the low side of the system (Blue Cap). Search youtube video for refilling a system before performing this procedure.

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