Hi guys, a visitor from another forum (electrical) needs some help, please.

My niece's outdoor Goodman A/C is not coming on.

When I first looked at it, I found that if I manually operated the relay at the A/C unit, the compressor and fan activated.

So, I had my nephew replace the relay, no joy. He and his friend also replaced the inside thermostat no joy.

I went back yesterday and verified that the gas furnace's (Lennox) low voltage transformer was putting out voltage. I got 28 V at the output of the transformer.

I also jumped the feed and return wires (red/white) at the A/C unit and verified that there were no breaks in the cable with an Ohm meter.

I reconnected the leads that fed the solenoid and verified voltage at the solenoid pins.

I also pulled the fuse on the furnace's circuit and verified that it was not blown.

No joy!

I can still manually operate the solenoid and get the A/C to come on.

What I suspect, at this point anyway, is that the solenoid at the A/C is not getting a ground signal to pick the relay's solenoid.

I, however do not know where this ground shot is supposed to come from. Does the control board on the furnace control the trigger signal or is it controlled by the thermostat. (I suspect the control board.). Is there any way I can force a pick sequence by setting a jumper to ground from the control board at the furnace to verify a board failure?

I need to go over to my niece's home this evening. I'll see if I can get pics of the units and schematics.

Can you please take a look at this item and give me some direction?

If this question is unanswerable in this forum, can you please tell me why.

Hello - Is anybody here?