A tech here at Appliantology had an issue with a Kenmore Whirlpool dryer that kept showing the customer an AF error code. Looking up that code in the tech sheet, we see this description:

Wow, this is some fancy modern dryer! Apparently, it's equipped with an anemometer to measure the exhaust airflow so it can alert the customer about a clogged vent.

Our tech checked the vent outlet and got good airflow. So why is the dryer throwing an airflow error? Maybe that swanky airflow sensor is out of spec!

Let's pull out the schematic to see how we troubleshoot this anemometer.

Hmm... well that looks like a pretty standard dryer schematic to me. No airflow sensor in sight.

Maybe if we look up the service mode error code that will have some more precise info for us on how this dryer says it measures airflow.

Well that's no help -- it doesn't give us any more info than we already had!

At times like these, you need to dig through all the info the manufacturer gives you. They often like to hide vital troubleshooting information and specs in odd places.A common place is the dreaded dummy directions.

Dummy directions are what we call the part of a tech sheet or service manual that give you step-by-step troubleshooting directions, which are notoriously imprecise and unhelpful. This is why we call them dummy directions -- because if you slavishly follow the directions without engaging your own critical thinking, you're a dummy!

However, while you almost never want to follow the steps they give you, this part often contains useful info, like so:

Aha! They finally reveal the secret of how they "measure" airflow, and it's nowhere near as fancy as we might have thought.

This is a piece of algorithmic information that tells us how the control board approximates the airflow -- it's just by comparing the input that it gets from the inlet and outlet thermistors. Mystery solved!

And there's another spec you'll notice that's only given here in the dummy directions -- the spec tables for those thermistors! You can see the outlet thermistor specs above, and the inlet thermistor specs are on that same page:

So with good airflow from the vent, this means our tech's next troubleshooting step is clear: he needs to check that the inlet and outlet thermistors are in spec. If either of those thermistors is lying to the control board about the temperature, then it could trigger that AF error.

This just highlights the importance of being thorough when reading our technical literature. We never would have found the information we needed about the now the dryer approximates airflow without exploring the whole tech sheet.

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