Let me see if I remember this. 1000mbar=1bar~14.7psi. This is equal to atmospheric pressure. If any of you diesel owners out there are ever messing with your vacuum transducers, the vents are usually marked "ATM", for atmosphere. Anyway, anything less than 1000mbar(negative pressure) is vacuum. Are you sure your guage isn't marked in/Hg? Don't worry about applying too much vacuum with a hand pump. In fact it's the perfect tool for the job. What kind of ACC problem are you having anyway?