a/c, temp gauge, no heat

[tntinnd]

Okay, so I basically only know a little about cars, and that is from problems with my car or past cars. So be gentle.

I have a 95 corsica, 2.2, 4 cyl. The first thing I noticed was the temp gauge "dancing". Usually it doesn't do it around town, until I am idling then it shoots up...sometimes to the 3/4 mark, never over. Now it is doing it more often, even when not idling. Usually at highway speeds it stays pretty constant at around 1/4 mark, but now "all" the time. Next problem is that around the end of summer the a/c went. The blower or fan kicks in, I can hear that much but no cold air coming and my car doesn't bog down like it normally would when I flip the a/c on.

Newest problem started happening a couple weeks ago, the heater is alternating between blowing cold air and warm air. Again the fan kicks on, defrost sounds fine and all that, but pretty much no heat coming out on vent, heat or defrost. This is especially true when sitting. Usually when I get to highway speed it will alternate between cold and warm for the entire 30 mile drive to and from work. We were told it may be the heater core, just wondering if you had any ideas before I take it to the shop. I kinda wanna know what I am up against. Could it be a faulty thermostat? Thanks in advance for any help.

[jsgold]

For the second time I will try to reply. System seems screwy, just deleted my post when I tried to send it.
Anyway...

Skip the a/c problem for now. Need more information on that to be of help but most likely just needs charged. However you may have R12 refrigerent so this should be another topic for later.
As far as heat goes, yes, thermostat could be stuck partially open. Have you checked your fluid levels in both radiator and overflow? Are you losing coolant? If not, most likely stat, replace and have system flushed. Should not be very expensive to do both. While I have flushed my own systems I have a hard time disposing of old fluid. Anyway, advise on your coolant level asap. A low system will do exactly the same thing and could cause you problems. Advise

The heater core can be plugged and causing this too, but, start with fluid levels first.