94 Cav. Fan, Brake, Eng. Temp Problems

I have a 94 cav 4dr vl, The fan over the radiator only comes on when I engage my a/c. Otherwise the care heats up to the quarter mark, then the half way mark. By this point the car will no longer accelerate but surges and vibrates horibbly. Also when I stop in this temp zone, the brakes seem to drag, they don't want to let go. The car also vibrates when cool but not as bad, and none of the other symptoms are present. Does any one know what might be causing this. By the way my a/c clutch does not engage even though turning on the ac engages the fan.

A/C activation will turn on the fan even if the A/C system is empty-it's what it does.
Suspect a bad coolant temp sensor not turning the fan on when it should.
Dragging brakes is another matter...nothing to do with the engine.
Shaking engine can be caused by an ignition problem, a timing problem, a valve timing problem, an injector problem, or a blown head gasket/cracked head-all of which will cause misfires/rough running.
What engine ya got?

For starters thank you for your reply. I have a 2.2L, also the brakes don't drag nor do any of the other problems arise unless the car reaches the half way mark on my thermostat. I replaced the Head gasket in this car about 2 years ago. The brakes and transmission have both been serviced and inspected recently (within 1 year) and with this in mind and the fact that the temp has so much to do with it is what makes this problem almost imposible to figure out. I am going to check the coolant temp sensor first and see what happens. Any further thoughts or info greatly appreciated.

OK, the brake problem should have nothing to do with the engine problem. They are two separate entities.
If the engine runs worse as it gets hotter-the map sensor would be a good place to start. I had a 2.8 do that same thing.
Check IAT sensor too(if equipped).
Ya might wanna check all the grounds to the ECM (on the back of the engine block where the negative battery cable goes to.).
Also check the ground/mountings to the ABS computer-Malfunctioning ABS can cause the brakes to do weird things-heat changes already unstable resistances. GM cars are notorious for bad comp grounds.
Keep us posted.