I have a Lennox HP-22 heat pump with natural gas back-up. I want to replace the original Lennox thermostat (36G6901) with a programmable thermostat. I purchased a Hunter model #44133/144132 programmable thermostat that "works with all Heat & Air systems".
The Lennox Thermostat letter connections and descriptions ara as follows

A Ambient Compensating Thermister
Y Defrost relay
L Service light
X Common
E Emergency Heat relay
R Reversing Valve
M Compressor Thermostat
F Blower relay
V 24 volt power

Hunter Technical support gave me connection points for all except "A, Y, and L".
L is the service light which is not a big deal.
The ambient compensating thermister and defrost relay concern me.
Why are these two wires at the thermostat? Shouldn't these control functions be
located in the heat pump control board. I am an electronics technician so I can fabricate the necessary circuit or components to maintain these functions if necessary. I went through this in 2005 with Honeywell and they left "A,Y,L, and E" disconnected.

Any help here would be appreciated!