if your existing thermostat is
marked...
RH / R / VR / 4
RC / VC
air conditioning compressor
Y / C* / M / O
W / H / B
G / F
heat pump compressor
Y1
10
label the wire with this
sticker:
RH
24 Volt
RH
RC
24 Volt cool
RC
Y/0
Y/0
W/B
heating
W/B
G
fan
G
Y1
Y1