Replacing my main contactor again due to cold solder joint caused by corrosion on the timer control. I tried bypassing the timer, because my digital thermostat (Honeywell rth 7000 series) already has one. Have the yellow from the thermostat going to one side of the coil on the contactor and the brown going to the compressor on the other side. Thing is, I check for voltage on this wire, and I've got nothing on any of the wires coming from the thermostat, which shows that it's on. I'm just checking for that 24vac point to ground, so I believe I'm doing that right. I just don't know where the 24vac is coming from. I'm a little frustrated, and it's 87 degrees in the house right now. Some help would be great.

If I`m reading you right, small wire to the opposite side of contactor coil is supposed to be common back to the furnace circuit board,which shouldn`t have a 24v reading, you won`t read 24v on the yellow wire until the tstat is set to a/c and this should pull the contactor in,which tells you that you have 24v to the contactor. I hope this helps as I`m not totally sure of the question

Found I had blown a fuse in the thermostsat wiring cb in the upstairs air handler. I do remember that wire sparking a bit during my replacing the contactor because I didn't hit the breaker to all the ac (just the outside unit). The brown wire in question comes from the other side of the coil through a hot gas switch, high pressure switch, then to a common on the defrost control. Going to try it like this after replacing the fuse, and go from there.

Got it. Everything working great.