Label all wires so you can return to the original setup.
The colors are not standard but the terminal designations may be good enough.
With four wires, each being hot, heat, cool, fan
and a voltmeter
you can confirm the function of each wire.
Find a wire (probably red) that gives at least 24 vac to each of the other three wires. This is the hot lead. Each of the other three wires taken two at a time should not have voltage between them but should read a few ohms.
Jumpering this lead to each of the other wires should give heat, cool, or fan.
Almost all of the $100 is the cost to have someone else assume the risk in this project.
Last edited by Wuzzat?; 01-20-2013 at 04:51 PM.