Why dont my cooling fans turn on after turning heat on high?

Hello, yes - your fans should only come on when needed. When you turn the AC on - or defroster - or climate control in general, you are asking for the condenser fans to come on, which is the same as a cooling fan for the radiator. This is normal. If you have poor air flow, like the car is idling for a long time - the fans may come on if the engine reaches a certain temeprature. I would definitely ensure all air is purged out of your cooling system in any case; I would not expect temperature difference of a great magnitutde between the upper and lower radiator hose... Some, yes, but not big. If you need another opinon, seek guidance at a local shop near you. https://repairpal.com/auto-repair-near-me Click the link or call us at 877-913-1554. We'll gladly find you a certified RepairPal shop in your area.