Renegotiating after home inspection

[Chris M.]

I am under contract for a small 750sq ft condo.  The only issue was that the AC was about 10 years old, and the temperature differential was 15 degrees.  I guess this isn't the worst thing in the world, but the inspector said the AC would probably need to be replaced in the next couple of years, and from what i read, this temp differential is satisfactory but so close to being unsatisfactory.  I read a few things that said HVAC pros like the differntial to be between 18-20. I live in florida, so aside from the cost of replacing the unit down the line, it may take a long time to cool the place down.  It is only 750sq t though so this might not be a problem.

I would like to ask for a discount but I also want to be fair.  The asking price for the house was $84k and we settled on 83k.  Would it be fair to ask for a discount because of this AC?  This is my first home purchase and a price tag of 4000 or so for a new AC is frightening.