I have a 1984-vintage Lennox heat pump/electric furnace system (two-stage heat, single-stage cool) with a manual Lennox thermostat. I'd like to install a programmable thermostat. I purchased a Honeywell RTH7400, which claims compatibility with multi-stage heatpump designs, but the wire labels on the old thermostat are almost entirely different from the Honeywell's wire labels.

Here's what's on the old thermostat, with wire names derived from the circuit diagram in the manual:

VR (jumpered to V) (red wire)
R ("rev relay") (yellow wire)
F ("fan relay") (green wire)
M ("comp contactor") (white wire)
L ("service thermostat") (brown wire)
Y ("supl ht relay") (blue wire)
A ("ambient compensating thermistor") (black wire)
X (no name, but appears to be wired to the emergency heat light) (orange wire)
E (emergency heat relay) (no wire connected)


And here're my options on the Honeywell unit:

Rc/R
R/V/VR
O/B/H
Y/Y1/M
G/F
C/X/B
L/F
E/X/X2
Aux/W/W1/W2

I guess I'm looking for the purposes of each of the Honeywell's connectors so I can determine which wire goes where. Has anyone tackled this? There doesn't seem to be clear documentation of the wires' purposes anywhere on the Honeywell support site..

Thanks,
Ryan

 

VR (jumpered to V) (red wire)Rc-R jumper
R ("rev relay") (yellow wire)O or B depends on if valve is on or off in heating mode.
F ("fan relay") (green wire)G
M ("comp contactor") (white wire)Y
Y ("supl ht relay") (blue wire)E/Aux jumper

Follow the wires below and see where it goes to.
L ("service thermostat") (brown wire)
A ("ambient compensating thermistor") (black wire)