Overview

Honeywell HE280C2010/U Higher Capacity Whole House Bypass Humidifier

Controller Images

Schematic

Here is the schematic that I put together based on some testing.

You would think that the GND pin on the 555 would go to ground via a pullup and that would be that.

Other thoughts:

• D2 is a zener diode which acts as a voltage regulator for the 555 chip.

555 Timer Reference Diagram

The Fix

Since the solenoid was no longer activating, it seemed like a replacing it was in order. The replacement solenoid that I purchased was rated 24 VDC but didn't activate when connected.

I opted to bypass the 555 timer circuitry by pin 4 of the jumper (JP3) to ground.

References