Trying to replace a 30+ year old mechanical t'stat with a Honeywell TH8320. My thermostat is so old that even though I have found pictures of it's sub-base online, the terminal markings are some what different. By that, I mean instaed of having G,RC,Y,RH,and W, mine has G-F,Y-C,4-M,W/H and RV. There is a blue jumper between the RV and 4-M terminals. Can anyone provide a translation of these old markings to the new standard variety. I have an old Carrier A/C with Bryant air handler and electric heat; nothing fancy at all. Can't locate the old scematic for the handler's wire connection.

Go to the Bryant air handler, open it up and see how the thermostat wire are there. We can then tell you how to wire at the thermostat

It looks to me like:

G-F (Green, Fan)
Y-C (Yellow, Cooling)
W/H (White, Heat)
RV (Red Voltage)
4M (?? Possibly for motor on stat)

If I were a betting man, I would wire it thusly:

Red-R/C jumpered to RH
Green-G
White-H
Yellow-Y
And if it's digital readout you'll need a common from the furnace to the stat unless it's powered solely by batteries. Use any unused wire on the existing stat wire, and hook it up to C in the furnace, C to the stat.

This would follow standard wiring conventions, but it's still just an educated guess.

Good Luck, and I hope this helped.

Thanks. The wire from the thermostat comes through the closet wall and attached to a terminal board on the side of the air handler. There are 5 screws there labeled, Y,G,W,4/R and X/F. Only 4 wires of the house wire are visible with the yellow connected to the Y,green to the G, white to the W and red to the 4/R. I do not see any blue wire on this end of the thermostat wire. It appears that the 1976 installers just cut off wires they did not need or use. There is also a short segment of thermostat wire running from this same terminal board to the bottom of the compressor unit. Two wires here; a red wire connected to the X/F terminal on the air handler and a white wire connected to the Y terminal along with the yellow wire from the thermostat. I have found internet pictures of this same old thermostat but the terminals in mine are labeled differented. For instance, mine is G-F instead of G, Y-C instead of RC, 4-M instead of Rh, RV instead of Y, and W/H instead of W. Any help in determing what terminal could/is be used as the 24V common will be appreciated. I certainly don't want to have to run this new TH8320 solely on battery power.

Even though the blue wire in the old thermostat is cut off and not used, I think I can pull enough to strip the end and attach to a 'C' terminal.