ajority times, the problem is with the low pressure of gas.. in years of use, gas pressure becomes less due to leakage or other issues.. so it is the repair guy who will check the gas pressure and refill if required
2nd but way less comon is leakage of the outer unit capillary.. this is tested by using foam soap water on them, but it requires opening the outer which you shouldnt do yourself
3rd and again very common is low voltage, but i doubt this is your case, since voltage is high these days due to rains and free dollars for IPP, .. but it could be.. you can check by using a voltmeter..
another tricky but rare problem is the AC itself going low amperes.. most of the times it is due to low gas pressure itself, thus ac is not going to the usual 8-11 amps it goes while on high torque... but there could be other issues with the kit.. again repair man is your best man..!!!