95 grand am overheating why?

car has the 3100 series eng. coolant came from the spout in firewall. so we took dash apart and found broken pipe on heater core and replaced the heater core(*&%$#)! car now starts to overheat,it didn't before the busted core. i checked fan by unplugging and giving power to the fan and it spins. i called myself bleeding the air out but it still tried to overheat. whats the proper way to bleed it out? cap on resevoir or not? now the fan came on once when it got to 220, it cooled then shut off,when it got back to 220 nothing came on and it went for the red. is there a relay for the fan? if so where is it located? what would keep it from coming on? also when the ac switch is on the fan still doesn't come on but the ac is low on charge also. i just don't understand,should we go ahead and put in the coolant temp sensor? haynes manual says it is on driver rear head but i think i see it on the front one. i will check for trouble code also:banghead:

Id say thiers an air pocket still trapped in the heater core.
Turn the heat to high heat with the blower fan on low.

Purge it with the resivoir cap off, if you dont have the bleeder on top of the water pump recirculator tube(black, brass fitting)

Fan relay should be right by the rad and fan.
Temp sensor is on the driverside under the TB.

If the AC is low (pressure low) it probly is not engaging the AC compressor, so the fan probly wont come on..

thanks xero! i do have the bleeder,i put in a new one. can u go into detail for me on how to purge the air? and also will the air keep the fan from coming on? there is 2 relays on the core support,one to the pass side and one to the driver's side,im sure the pass side one is not it cuz when the ground was loose the starter would not work. so i guess it's the other one. how do i find out if there is a problem with the relay. any help u can give us will be appreciated. thanks, eddie

Its not to difficult to bleed the cooling system.
Bleeding Your Cooling System (http://www.automotiveforums.com/vbulletin/showthread.php?t=718130)

Testing relays are a little more tricky.
On the side on the relay is a diagram that shows the circuit(s) with numbers to identify each terminal and power/control circuitry.
I should probley do a small write up on this with some pics to help do this as relays vary, one has a resistor inside and others may have a diode.

Heres that page....
Testing Relays (http://www.automotiveforums.com/vbulletin/showthread.php?p=4877593#post4877593)

Good Luck

on the relay,is it safe to exchange with another? also does the air in the system make the fan not start as it is supposed to?

yes as long as they are the same.

No air wont make the fan not come on....

The PCM commands Low Speed Fan ON under the following conditions:

The engine coolant temperature exceeds approximately 106°C (223°F).
The A/C refrigerant pressure exceeds 1310 kPa (190 psi).
The vehicle is shut off when the engine coolant temperature is greater than 140°C (284°F) and system voltage is more than 12 volts. The fans will stay ON for approximately 3 minutes.

The PCM commands High Speed Fan on under the following conditions:

The engine coolant temperature reaches 110°C (230°F).
The A/C refrigerant pressure exceeds 1655 kPa (240 psi).
When certain DTCs set.