Air con Vegas s40
 

Hi, last week noticed my air con stopped to blow cold air so today I bought STP ex chill gas with gauge to refill it. I did everything how instruction says but when I was refilling gas then gauge started to fluctuate and my compressor kicks on and off. So I can't measure what's the actual reading anymore so I don't know should I add more or not?

Gauge reading going up to 55 and when compressor kicks in then reading drop back to low and going up again. Maybe somebody got the same problem?