AC Leak/RPM gauge jumping
 

SO a few days ago the AC stopped blowing cold, and yes I live in Texas and you sometimes have to run the AC during the winter. Popped hood notice compressor not turning on, put on gauges and was low so I added a little freon. Worked well next day same issue. Checked low again. Put gauges on and added a little more and left on truck all day with motor off. Eventually leaked down to nothing. Seems like a major leak but nothing obvious. Gonna buy some leak detector tomorrow, wanted to ask if there are common areas that are prone to leaking? Its a 97 disco with 198000 on it. I've had it for almost 3 years now and the ac has worked flawless up to this point. Also for some reason my RPM gauge has started to bounce around from time to time. RPMS are perfect in the truck just gauge acting silly. Replaced battery and alternator about 6 months ago.

The tach operates off the alternator, clean terminals and grounds and see what that does. It could be a sign the alternator regulator (diodes) is going bad too. As far as the A/C and loosing freon there isn't a common area, it would be the same for any A/C system. I'd evacuate the system and check your line connections which are the number one cause. You've got a lot of miles on them, bound to be suspect by now. I added several ounces of freon with a leak sealer to my 214k Jeep this summer and it's lasting a whole lot longer than I thought it would, cycles the compressor when in defrost recently.

I added refrigerant last summer and the hard line below the coolant tank split right where the clamp to the body was located. Seems they corrode due to the aluminum line attached to a steel clamp can cause corrosion. I used a splice made specially for A/C lines, has worked well so far.

I replaced the alternator and that fixed my bouncing tach. Maybe a bad ground if it is intermittent. Try putting a jumper cable on the alternator frame to the body ground and see if it gets better.