[Richard]

Hank,

The mental exercise you will face when making your own board from a available relay board, is how to control the high low fan speed outside. Cause if you cypher on the outputs from the Tstat, you will see that when the second or HI kicks on, the outside fan is getting signals to run lo and high from the Tstat. The existing board has a circuit that handles the two inputs and doesn’t feed the outside fan motor voltages to both the high and low windings at the same time. 

Here is how. Run the output of the relay for lo speed though the normally closed side of the hi relay. When the hi relay kicks in, it will take the lo side feed out of the picture. This way the motor will only see voltage on the lo or high windings, even if both the lo and high relays are activated by the Tstat.

       

I wouldn’t run the comp amperage through those wimpy relays, though I use them as I do on the current board, just to trigger the external motor contactors. 

This is my backup to my backup board. It has been tested on the SCS unit in my shop. Keep in mind I built this before Newell had developed a replacement board, and the SCS boards were made of unobtanium. Rhonda does not like to be hot, and I wasn’t going to get stuck with a non op unit.