[JustSayGo]

You are right. The compressor needs to run for a few minutes to cool. Low-side A/C pressure is measured after the compressor has run long enough for the pressure to stabalize or read just before the compressor cycles off. Even 10 seconds isn't enough time to check the pressure accuarately. Sounds like you are describing an A/C system that is empty. As soon as the compressor clutch turns the compressor, low-side system pressure drops and the low pressure cut out switch cuts power to the clutch. If there is any restriction in the service can hose or at the schrader valve the guage won't drop with the low-side pressure.