Hello. I'm new to the forum. I have a problem...My 2000 Blazer blows hot air constantly and I hear a clicking (like a blinker, but the blinker isn't on) behind the glove box. I charged the A/C a couple years ago and it worked for a few months, but then quit blowing cold. I tried it again the following year, but with no luck...the gauge used to charge the A/C reported a "malfunction". Every few months I have to add antifreeze to radiator and there isn't evidence of a leak on the ground. A lot of issues...are they related? Thank you!

 

The clicking behind your glove compartment is probably your low pressure switch, although it might be a relay... I'm not sure where they are on the post-facelifted Blazers.. the AC relays are under the hood in my 97.
AC systems are broken down into seven operating conditions, with condition one being normal operation, and the remaining conditions resulting in insufficient cooling.
Low refrigerant level, excessive refrigerant level, damage to the condenser fins, desiccant in the accumulator becoming saturated, introduction of air and/or water into the AC system, blockages in the system, excessive compressor oil, faulty low pressure switch... all of them can cause your AC system not to blow cold. If you want to narrow it down further, you'll need a manifold gauge set and some instruction on how to use it and record system pressures. That'll help isolate the problem so it can be identified.
Your coolant/antifreeze loss is a separate matter. If you're not seeing signs of it anywhere in the engine compartment or on the ground, it could quite possibly be going out of your exhaust pipe. The GM 90 degree V engines have a bit of notoriety for eating up gaskets - namely, the head gasket, but especially the intake manifold gasket.