Heat Pumps and Electric Heating - What does the 'A' wire on my old Robert Shaw thermostat do?

I am replacing my old Robert Shaw thermostat (model: D34020) with a new Honeywell thermostat (RTH7400). The Honeywell installation manual doesn't mention a wired connection labeled 'A', and the Honeywell telephone technical support doesn't know what it's for either. The new thermostat has the following terminals: C, G, Y, O/B, R, W2, Y2, AUX, E and L. Honeywell tech support says if they know what the wire does, they can help match it to the proper terminal. Unfortnately, support for Robert Shaw products isn't available on the weekend. Does anyone know what 'A' wire on my old Robert Shaw thermostat does?

Honeywell tech support says if they know what the wire does, they can help match it to the proper terminal.

Id check on that A color and see where it goes in the blower unit and what it does. I have no idea. One book I have say A is. Normal compressor opertion relay/always on in normal mode off in emergency mode.

This is out of a Hunter tstat set up

ED;)

On my Lennox system, 1984 vintage, the circuit diagram labels "A" as the "compensating thermistor." I'm still working on what implications ignoring that wire may have for installing a new stat.