Ducane B050A3B, how do you get the limit switch to reset? Changed filter, checked the registers, changed batteries in thermostat and the LED is still flashing 4 times.

Most have a button between the 2 spades that wires are connected to,, if none u will have to replace

Quick idea before throwing in the towel is to power off the unit (via breaker or disconnect box (http://www.thermal-medics.com/a-c-image-glossary/)) completely. Wait a minute or two and power back up.

Thermal,, now you know this part is on a furnace,not the ac., just kidding, good advice and it don`t cost nuthing

You are right I just don't do enough work on gas here in PHX. Like the line from the Dirty Harry movie "a man's gotta know his limitations". I usually keep my mouth shut on gas stuff.