Hi Labman,

I had a bad relay (LY2 24 VAC), so I marked the wires on piece of paper to take it off and install the new one. The problem that I lost the paper somehow and I don't have a clue how to install the new one. I know that the I/p is 120 VAC and the o/P 24 VAC. How ever I have 6-wires should be connected to the transformer, and it seems like the colors are not right coded. I have a gray thick wire is coming from the pressure switch, thick black color is coming from the inducer, thin white color is coming from a pannel,thin black wire is coming from other panel, thin red wire is coming from the other 24 relay(or contactor), and finally a red thick wire I can't track it. I know that 24 vac should go to the TH-W on the S8610U module, and the 24 ground as well. However, I don't know which is which. The thin white and black wires are on the side of power supply, but are connected to interface board. Please, send me a wiring diagram or reply to me how I connect this 24 transformer as soon as you can because I have two babies and I can't afford bring some one to repair it. Thanks a lot

I do not have a wiring diagram to give you. If the one that was on the furnace has disappeared, you may be able to find one on the manufacturer's web site. A local dealer may help too.

I do not understand the 6 wires to the transformer. Did you replace the transformer or a relay? A transformer should have 4 connections, 120 in, and 24 out. There may be a fifth one, but it is not used and should be marked differently than the two 24 volt ones. The basics:

Usually there is a 24 volt AC transformer in the furnace with the secondary winding connected to a red wire running to the thermostat and a blue wire, common, to the gas valve, A/C relay, and fan relay. From the thermostat there will be white wire to the gas valve, yellow to the A/C, and green to the fan. The thermostat is wired to switch the power from the red to the white, yellow, and green as needed with the blue completing the circuit. Most thermostats and furnaces have the contacts labeled R, B or C, W, Y, and G for the corresponding wire colors. It may be wired to have the A/C control wires return to the furnace and its controls and then a second wire goes to the A/C unit. Internal wiring may replace the green wire if the thermostat does not give you the option of fan only or continuous fan. Digital or programmable thermostats may need the blue wire connected to them.

Either 24 volt connections can be used as the hot and ground. The hot is only connected to the thermostat and any control board. Everything powered by the transformer must connect to the other connection.

A simple relay should only have 4 terminals, power in, power out, and 2 coil terminals. The coil ground could be used as a junction for other wires going to the transformer ground.

You may have to follow the wire back and see where they come from to figure out where they go. If you need more help, post back explaining what you have figured out, and whether these wires go to the transformer or relay. Sorry I can't be more specific.

Thanks a lot for your reply.I figured it out.The colors I have are not follow the right codes.However, I traced them and I conntected them.The problem was solved.Here were my measured voltage on each wire:
Thin black: 110vac (coming from input power supply)
Thick black: 0 vg (is coming from inducer motor)
Thick Gray : 0vg (is coming from pressure swtich)
Thick red : 25 vac(is coming from sensor)
Thin red : 25 vac ( is coming from the output of the transformer)
White : ground ac ( is coming from the transformer as well)

I connected the relay as follow:

1. the input of the relay should be 25 vac so I connected the thick red which is coming from the sensor on one leg, and the other I connected to the white as a ground.
2.When the sensor get the signal the 25 volt will swtich the relay,so the connected the thin red(25) and the thin balck(110) to the swtiched legs.
3. I connected the thick black and the thick gray to the unswtiched legs.
So when the relay swtiched the gray will have the 25 volts to close the pressure swtich which will feed the TH leg on the module to generate the spark, and the thick black will get the 110 vac to get the inducer motor the power to run.

The furnace is working perfectly now.I have some troubles after connecting every thing because I lost the 25 volts, and I got only 13 volts which was very unusual.However, I found the reason that the cover of the wall sensor unplaced.When I put it right, I got the 25 volts back.

I'm sorry that my english is not that great, but I tried to explain what I did to help any other if they face the same problem.

Thank you again for your help

Hassan