You didn't say where you're from or what the weather currently is or what you expect for May, so......
Chicks need heat for the first 4-6 weeks because they do not have their feathers. At 6 weeks, they are virtually fully feathered and the need for high temps is gone. Warm, meaning 60-80 is just fine. Cold would mean below 45 at night.
They have to adjust and adjust they will, with your help. It's time to lower the temperature considerably every couple days and get them used to the real world. You shouldn't just plunge them from 80 degree heat, 24/7 to facing cool nights of 50 or less. They can take it fine down to 40 in May, IF, IF you've acclimated them gradually to lower temps. Raise the lamp a little, every two days or lower the wattage. Get them used to it and they will be fine, just fine.