old solar heater controller

KlausST said:

Hi,


No.

Your "variable resistor" is marked with "VR", which means "voltage dependent resistor" and is the overvoltage protection to the sensor input at the PCB.
And these VRx devices have nothing to do with the function at all, it is just protection. You may ignore them. These are the blue disks in the picture.

I guess you misinterpreted the VRs (protection devices) as the sensor.
But the sensor is off PCB (thus not drawn into the schematic) ... connected with wires.

So it is:
R2 goes from the output of U1D ... through the blue wire to the sensor, and back via the red wire to the PCB as input to R1 - R2 to U1D_input.


As the OP wrote in post#1:

Since the sensor is "wired" it is not "on PCB" thus not drawn into the PCB schematic.
But the wire connector (pad) is drawn ... and marked with the wire colors.

Klaus

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johnny78 said:

2 wires are 10k NTC

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