After my husband added coolant to my VW AC, that same night a rumbling vibration started (sounds like under the hood) - on/off on/off. It stays on when idle. (Manual transmission) Now the AC is coming on and off - cold, then barely cool - and with less power. Also, when I accelerate it falters, like I'm stepping on and off the gas pedal
Compressor cycling is caused mostly by low Freon levels or over charged system. Likely possibility is it has been over charged. Recommend taking it to an A/C Certified shop and having the system evacuated, vacuumed and charged to the correct amount.