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Independent Energy C-30 Differential Temperature Control Delta-T Mod

For non-variable C-30 controllers with OEM Delta-T settings of 20/5. This will bring your Delta-T to 8/3 for better efficiency in a wider range of cloud cover.
This procedure is fairly straightforward, and you are assumed to have the skills and understanding of electricity to perform this modification safely.
Always disconnect power, no warranty is made or implied.

R8 from 37.9k to 10.5k 1/8w
R9 from 96.8k to 102k 1/8w
2% metal films are preferred, but carbon 1/4w works with no issues.

Here is an excellent guide to Drainback Systems