Recently I remodeled a house and gutted the interior. My son-in-law asked if I wanted to look at the old Honeywell T87 thermostat before he removed it. I told him to remove it, after all, how hard is it to rewire 4 wires.

When it came time to install the new digital Honeywell thermostat, SURPRISE, it has 5 wires! I guess I am not as smart as I thought I was. The new thermostat is the common Rh, Rc, G, Y and W terminals with a jumper between Rh and Rc Those terminals all make perfect sense to me - Red is power (heating and/or cooling), G is fan, Y is A/C and W is for heating.

Where I have run into problems is the connections on the terminal block on the furnace. That block, which I believe holds the transformer and the fan relay, has 5 screw terminals on it. It looks something like this ---

-----------O Red to the condenser and yellow to the thermostat
------O White to the condenser and black to the fan relay
-----------O Blue to the fan relay and green to the thermostat
------O Blue to the thermostat
-----------O White to the burner and white to the thermostat

In addition, the red wire from the thermostat goes to the red wire from the burner.

Any help you could give would be greatly appreciated. With temperatures here reaching 100 degrees, I have to get this A/C working properly. Thanks in advance.

This is probably an old furnace, the blue wire from the thermostat is probably to lite the pilot when there is a call for heat. The "B" terminal in the thermostat is made from the red wire when the thermostat is set to heat on the subbase, do you have a "B' terminal in the new thermostat, if not then you could connect the blue wire to the red wire going to the thermostat ( this would lite the pilot when ever it goes out) the rest of the wires are normal -- red wire to R, green wire to G, white wire to W, yellow wire to Y. good luck, Mike