The temperature will vary depending on the season of the year in which you are taking the tour. Regularly from MAY to OCTOBER it is rainy season, so it is not so cold; from NOVEMBER to APRIL it is dry season so it is a bit colder.
In Acatenango, you can get from 0 to -5 ºC at the top and the campsite.
In Pacaya, you can get from 10 to 0 ºC at the top and the campsite.
In Antigua, you can get from 25 to 12 ºC in summer, and from 15 to 8 ºC in winter.