Have a Goodman AWUF300816BA Air Handler, Single Cool, Heat Strip (No Heat Pump) looking for wiring diagram for 5 wire programmable thermostat. Specifically can't locate on Air Handler 24 VAC Common wire terminal location.

There isn't always a low-voltage wiring diagram.

Typical terminal designations are:

C - Common of 24V Transformer
R- "High Side" of 24V Transformer
W - Energizes Heat Relay
Y - Energizes Cooling Relay (contactor in condenser)
G - Energizes Fan Relay

It may be necessary to trace out and see where the wires actually go. Typically a 5-wire cable will run to the thermostat, and then you will have two wires going to the relays (Common and then W, Y and G depending on which relay it is - this gives you the 24V to energize the relay).

All a thermostat does is connect R to W for heat, connect R to G for fan, and R to Y for cooling (cooling in "Auto" also connects G to R).

Hope this helps.

Thank you for your help. I don't have a problem with the wires between air handler and old thermostat. However, the new Honeywell Programmable WiFi Thermostat requires a 24 VAC common wire that was not used in the old thermostat.

What I don't know is where on the Goodman air handler is the "C - Common 24 vac connector to attach a wire from the thermostat? Currently, there are only 4 wires between the air handler and the old thermostat; Green, Yellow, Red, White.

I don't see a connector available for the black/blue C Common 24 vac wire on the air handler so I don't know where to connect the wire. I had hoped there would be a 5th wire, black/blue connected from the air handler to the 24 vac location and not connected to the old thermostat. At least I could locate the wire and use it. I had to run a new thermostat wire with 2 conductors and only use one of them whenever I learn where to connect it on the air handler.

Thank you.

Okay, as long as you have a wire, go to the air handler where all the connections are for the thermostat.

A 24 Volt transformer has either two screw-terminals on it, or a pair of low-voltage wires coming off it. If you trace where the "R" from the thermostat goes to that will lead you to the transformer. (The R may come back to the airhandler to a terminal strip, a circuit board, relay, etc).

The "R" is the "High-Side" of the low voltage transformer. Like I said there will either be two terminals (screws) or two wires coming off the low voltage side, and two or more wires that connect to high-voltage side of the transformer (the power going into it). So whatever wire comes from the R on thermostat keep tracing it back until you find a "heavy" metal transformer. The Low-voltage wire that the R is NOT connected to is your "C" or common. The common wire wire will be connected to the contractor in the outside condenser for A/C ( the other wire is the "y"), and to the fan (blower) relay (these are usually brownish with a bunch of wires connected to the NormallyOpen or Normally Closed contacts on it - there is also a 24V coil that energized the relay and turns on the fan.

Connect the wire you ran from this screw terminal (if it is that type), or remove the wire-nut on it and connect your wire to this. It's a good idea to shut the power off when you do this so you don't short out your transformer.