Purpose of a Heat Assisted Limit Control?

[Ted Mosby]

I had a no heat call last week, found a faulty limit control to be the cause. It was on a Ruud down flow furnace. I understand that they would mount a limit control on the blower housing, as the heat would rise if the blower wasn't working properly/lack of airflow etc... But what is the purpose of having a heater in the limit switch? The best explanation I could find was that since it is in the return side the temp wouldn't get as high there as it is inside the heat exchanger cabinet, so they pre-heat the limit switch to within something like 10 degrees of its limit. I don't understand the benefit of doing this instead of just using a limit control with a lower heat rating. Can anyone enlighten me?

[Admin]

I've never worked on a HALC but from what I've read your explination sounds right.

What was the temperature rating of the HALC you were working on?

I suspect the rating is lower than a primary limit.  Lowering the HALC temperature rating could cause nuisance trips.  If there was a bypass humidifer installed it could cause the return air temperature to increase and might trip the HALC.

I don't think manufacturers use HALC's anymore, probably because they were a bad design to begin with.