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Is this what you are waiting for?
C-30 temperature
differential controller.
I know you're probably looking for someone who has one and who can help you out I know the principles behind it but there's so much information you left out that I'm trying to piece it together.
I hope this will help.
Have an old Grumman Sunstream control unit, previous owner said the heat exchanger was calcified.
forum.heatinghelp.com
If you do not have the original owner's manual and if it is a CF 100 then
you have to join this site in order to download the PDF document your going to have to give a credit card I think it's a free trial I'm not a member so cannot recommend it. But the site is legitimate.
Grummam Sunstream CF100 Counterflow Module Solar
www.scribd.com
If you could perhaps make a block diagram of your specific setup; solar panel battery, Maximum power point tracking (MPPT) etc. then I would be happy to assist you.