[HollywoodHicks1]

Ok, I know that you all may be thinking that I am a little slow from this. Ok, Tuesday I was checking to see if the heater was operating in the 1990 DeVille, then my Service AC light came on. I looked under the hood to check everything out. Everything was cool except I was low on coolant. Does the lack off coolant mean that I can have no air or heat? If so, what kind of coolant would you recommend to use, and do I or should I put anything in the radiator? HELP ME PLEASE!!!:crying:

 

[vanaisa]

if "service AC" light comes out in control centre, it means, that you have refigerant loss. Its not connected with low coolant. And - with low refigerant AC just switch off compressor and runs "economy" mode (only heating).

 

[Katshot]

vanaisa's right to a point. The heat and A/C issues are most likely NOT connected. Low coolant will cause a no or low heat condition so in an effort to regain some heat, I would top-off the coolant with any name brand coolant like "Prestone" etc.
There are several things that could be the cause of the "Service A/C" indication so I would suggest a little more investigating.