Low input voltage is the voltage going in:
So I would check the relay, the wire and connector at the sensor. Check the
manual to see which is the input, and take a voltage measurement with the
key on, and then put a fan forcing air into it, to see the voltage change.
The sensor reads the amperage needed to keep the wire heated to a specific
temperature, when air passes it. Better yet, a square wave meter or lab
scope would be far more accurate. (Before SPX/Sperry-OTC bought out TIF,
they used to make a square wave counter for a digital VOM) I think they
Otherwise, you'll have to buy an OTC or Snap On Vantage if you want to read
square waves. For the do it yourselfer, voltage readings IE. voltage drop or
amperage is fine.
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