Yes, gauge can be zero'd. Be sure you have no trapped pressure in manifold. I assume you mean 35 psi rather than 350 psi?

good luck

That wasn't a typo. It reads 350. (The photo I posted was taken with the gauges hooked up to the A/C)

I don't think there is any trapped pressure. I am able to move the needle with the screw in both directions, but it is so far off that I'm unable to reach 'zero' from either direction. I may take the back off the gauge and see if I can do anything from there?

From your description, the dial would have to go down from "0-pressure" position to reach what was in your photo. This should not be possible w/ a bourdon tube gauge. Something is "out-of-whack" in the gauge mechanical movement.

OTOH, perhaps the adjustment has enough range to rotate CCW to 350 psi position?

good luck

I think I'm describing it wrong.

At rest, the gauge reads 350psi. When I hooked it up to the system, the needle moved from there clockwise thru 500 and past zero - and ended up at 75psi.

The zero-adjust screw does not have enough range to get it to zero. I took the back off and can see nothing amiss. I have no idea what happened to it.

However one could interpolate the reading in my photo to be about 275psi. It was about 85 degrees that day and very humid. If that a bit too high for the high side?

(I plan to contact Uniweld about a replacement gauge)

<EDIT> Look what I found on eBay: :)

http://www.ebay.com/itm/160948945673?ssPageName=STRK:MEWNX:IT&_trksid=p398 4.m1439.l2649

My replacement manifold gauge arrived, and I instinctively was going to use teflon tape on the threads. but then I hesitated.

Doing some googling I found mention of using blue loctite on the threads. Do you guys have any thoughts on what I should use?