Oldsmobile/Buick Repair: Heater Core and Heater Control Module, brain tumor, olds bravada

Question
I have a 1998 Olds Bravada truck.... I just had the heater core replaced for parts and labor $ 900.00.  Anyway, the next day - I realized that only hot air was coming out of the vents with A/C on and defroster at 66 degrees too.  Now I take the truck back to service and they tell me that the Heater control Module is dead.  Should they have checked that when they replaced the heater core or could they have broken it some how and/or does it all relate.  My husband usually handles all the car affairs and died of an brain tumor so now I'm taking care of it all and I really don't know much about it - please help!!! Many thanks.  

Answer
Hi Carol,
If the A/C was working when you took it in, they may have just left something disconnected.
I really don't know if the refrigerant needs to be removed to replace that heater core.
The answer actually hinges on weather it was working when it went in.
Van