wrote:
Hi,

I currently have a Robertshaw 300-208 thermostat running my Luxaire
heat-pump and (some other brand) electric furnace as auxiliary heat.


I just bought the Honeywell RTH8500 thermostat to replace it.


There are two labels on the Robertshaw thermostat which do not
correspond to any label referred by the installation manual for the
Honeywell thermostat : "24V" and "24V(c)".


I've included pictures of the current wiring. Because some of the
labels are hidden in the pictures, here's a top-to-bottom list:


W1
Y1
G
R
24V
24V(c)
O
B


Here are the pictures:


http://www.jpti.ca/IMG_6107_2.JPG
http://www.jpti.ca/IMG_6102_2.JPG
http://www.jpti.ca/IMG_6103_2.JPG
http://www.jpti.ca/IMG_6105_2.JPG


Pictures! What a radical idea.


Can anyone tell me which of my wires I should connect to which
terminal on the Honeywell ?


Robertshaw
24V is power to the control circuit
24(c) is the 24V common (like a neutral in a power circuit)
R is 24V power to the switches in the stat - jumpered to 24V
W1 connects to R for heat - 1st stage - heat pump
Y1 connects to R for cooling - 1st stage
G connects to R for fan
O ??likely 2nd stage heat - electric heat

You don't give the terminals for the Honeywell but R-W-Y-G are standard.
You may need 24V common to power the Honeywell control circuit - that is
the blue wire. Orange is probably the Honeywell second stage heat.

As the temperature falls to the set-point for heat, R-W1 connect to run
the heat pump. Maybe 2 degrees cooler R-O[probably] connect for electric
heat.

(I didn't google either Robertshaw or Honeywell. With heat pump and aux
heat the Honeywell very probably needs to include 2 stage heat.)

--
bud--