GMC Repair: 2000 Denali fron ac not cold, gmc yukon denali, 2000 gmc yukon denali

Question
I have a 2000 GMC Yukon Denali 4WD 5.7V8. with 99 body style.
Rear AC blows cold. Front AC takes 30 minutes to blow cold.  I usually try it on high with Max setting.  Where do I start?  I don't think it's a problem with coolant level.  Possibly related was a whistling/ relief valve noise from the rear passenger side of vehicle intermittently when the ac was on.  This noise has gone away since the fron AC stopped cooling.

Answer
Hi
It REALLY sounds to me like you do have a low freon issue.
I would take it to a good HVAC repair shop and have them diagnose it.
MOST places will give free A/C system checks, call around.
I Know alot of the major repair shops (Meineke, Midas, Pepboys, Firestone, etc..) DO offer free A/C check ups.
May take a few mins., but at least you'll know.
That is the first step I would tell you to do.
I Hope this helps.
Good Luck
Pawl