Ye Olde General Electric Thermostat


Old 12-04-07, 09:20 AM
Thread Starter
Join Date: May 2007
Posts: 17
Ye Olde General Electric Thermostat

Upgrading a 30+ year old GE heat/cool thermostat, running an oil fired hot air plus central A/C system to a programmable Honeywell thermostat. There are five thermostat wires. White, yellow, red and green are attached to W, Y, R and G terminals on the old thermostat and transfer easily to the new thermostat. But there is a fifth wire, color blue, that is connected to a terminal marked "2" on the old thermostat. Not clear how to transfer this to the new thermostat. Spoke with Honeywell for a half hour, no help from that quarter. The old thermostat has a mechanical three position heat-off-cool switch and a two position fan auto-on switch. The PC board trace for the fifth/blue/2 wire clearly runs to a soldered connection on the heat position of the three position switch, so fifth/blue/2 wire is heat related, but exactly what? The guess is to control a humidifier, which the system does not have. What is the function of the fifth/blue/2 wire, and how might it map to the new thermostat? Thanks.
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Old 12-04-07, 09:41 AM
Join Date: Aug 2007
Posts: 2,021
Don't do anything until you find out where that blue wire goes in the furnace. Reason being is there are 2 transformers when you have cooling with oil heat. One is for the cooling system and one is inside the oil burner primary control. They have to be electrically isolated from each other, otherwise one will blow; usually the one in the primary control. $$$ [you'll never guess how I know that, he he] Find out where that blue wire goes.
Old 12-08-07, 10:34 AM
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Join Date: May 2007
Posts: 17
Traced the mystery blue wire to the furnace. No connect! The blue wire at the furnace is coiled around the sheath. Only red, green, white and yellow make connects.
Old 12-08-07, 10:59 AM
Pete OldNavy's Avatar
Join Date: Dec 2003
Location: USA
Posts: 173
<EDIT> Seems you found your answer

Do you have a Model number on the OLD thermostat?

The above link has a lot of good informations but nothing with a 2 connection.

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