Which Temp controller

Yes a single PID controller mar be used for both heating and cooling. When I worked at Electro Scientific in southern Calif. we had a Watlow programmed to heat or cool to maintain a band of temperatures.

The high and low alarms were used to switch between cooling and heating using steering relays. I would have to study the current crop of Chinese PID units to see if I could rewrite the program to wok on one of them.

GeneK

I have been using a couple of REX-C100s from china and they perform well. In the UK they are about £12 each - so approximately $18.

For me, the program that they come with works well so the inability to program them has not been an issue. If you are trying to do something fancy then that could be a restriction.