Hey,I'm new to the forum, but I figured this would be my only hope to figure out what is wrong with my Monte.

I have 98 Monte Carlo LS 3.1L

First, the engine temp pegged to the right when idling, but once I accelerate it goes back to the left.WTF is this all about?:banghead:

Second, the air conditioning doesn't blow through the vents, but only through the defroster. Haynes Auto Manual says it maybe a clogged hose. Again, WTF is this all about?:banghead:

Have the cooling system, checked make sure the fans come on when hot, no leaks, good circulation.. Look for a bad vacuum hose somewhere, there is a vacuum storage tank inside the front of the lt ft fender well behind the inner shield. BTW welcome to AF

If you're low on coolant, you most likely have a leaking intake manifold gasket, very common on your engine. I agree with Max that the vent problem is a cracked vacuum hose to the HVAC system.