Unit was slightly undercharged from last repairs, causing condenser to lock out due to low pressure switch engaging. I had taken some refrigerant out due to over charging it at first then completed heating maintenance but never checked cooling side. I doubled checked the lines, condenser coil & evaporator coil for oil stains & leak detected everything & didn’t pick up anything. I told customer it was more than likely just under charged & went ahead & charged it up without charging him for it due to it being a mistake on my end. Mentioned if it were to happen again then we would need to do a more in depth assessment & see if there’s maybe a pin hole in the lines or in either coil. Again I didn’t find any obvious signs of a leak. Unit was functioning properly & not shutting off from low pressure switch again after charging it up.