HVAC has no C output

[EnoughWithTheCWire]

I am one of the lucky ones that has his HVAC in the craw space above his house (please note scarcasm). It is a b%#*% to get up there and after finally finding where the wires from my 3M-50 goes to, it saddnes me to see there no C output. Now, I know that if my HVAC has power it has Common Power, but I don't know where to get it from. I have an extra blue wire that is unplugged at both sides, but I am out of ideas of where to connect it to.

There are no capped wires and there is no output for "C". I have dedicated outputs for "G", "Y" ,I think the next one is "W", another random green wire, and "R".

Any ideas?

[blaine]

1. See if you can find the 2 wires going out to the compressor; one of those 2 wires goes to Y at the thermostat and the other one is the C wire that you could tap and use that spare wire to get it to the thermostat.

2. Or, you could use a 16VAC, or 18VAC, or 24VAC adapter (100ma or more). Connect one of the wires to the R at the HVAC (the wire that goes to RH at the thermostat) and the other adapter wire via a spare wire to the C at the thermostat. (16 or 18 preferred).

3. You could also use the 17VAC doorbell transformer if available; connect directly to the transformer.

R to RH and RC connected for 24VAC power
G to G for fan
W to W for heat
Y to Y for cool compressor
C to C for 24VAC common