The other day I turned on my ac for the first time since I got the truck. The air would get cold then cool then cold back and forth about every 3-4 minutes. I gigured it was a little low on 134, so I picked up a can today yhat has a gauge. After putting a little more than half the can in it is blowing nice a cold....problem is the compressor is cycling on and off. I watched the gauge and it is around 25 lbs then the clutch engages and it creeps to around 50lbs and the compressor disengauges and the pressure goes down to 25 again. This happens about every 45-60 seconds. Is this right????? Or do I have too much or too little coolant. The outside temp is around 73 and all this is with tha truck idling.