Review on Enhanced Aprvtio Refrigerant Leak Detector: LED Light, Halogen Leak Tester for HVAC Systems (R22 R410A R134A R1234YF), CFCs, HCFCs, HFCs - WJL-6000PRO 2021 Upgrade by Sean Julian

I had a slow leak at the low pressure Schrader valve on my 91-GMC Suburban. As he stuck the tip into port 134a, he quickly began chirping, with the indicator counts going from zero to 9 in a matter of seconds. After tightening the Schrader valve about 1/8 turn and cleaning the port with compressed air, the reading was zero, with no audible click, indicating bypass valve leakage. I saved $400 by fixing a leaking valve myself in minutes.