Heater only blows cold air

I have a problem with my heater only blowing cold air.  I recently change the blower motor compressor in my 2006 Avalanche.  Because the blower would not shut off after I turned the vehicle off, and it only blew at one speed.  I installed the part and it shuts off and changes speed, but will not blow warm air.  I have also noticed that when I do turn the air on the temperature gauge raises up over 210. When I turn the air off the temp falls.

Have you checked the coolant level.

I just recently had the oil changed and they were supposed to check that, but I will check it and see

Must've been the problem...?