ATS Won't Transfer back to Utility

Automatic/Manual transfer switch repair, wiring & troubleshooting questions
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New Member
New Member
Posts: 1
Joined: Sat Jan 12, 2019 1:32 pm

Sat Jan 12, 2019 1:35 pm

I have a 25kW Generac Guardian generator with a Generac 200A (model 0049451) ATS. When utility power is lost, the generator starts normally and the ATS transfers load to generator as designed. However, when utility power is returned, the generator turns off as normal, but the ATS does not transfer load back to utility. I have to manually transfer from generator to utility. Any suggestions on how to troubleshoot this issue?
Site Admin
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Posts: 174
Joined: Sat Aug 04, 2018 8:46 pm
Location: Clawson, MI

Sat Jan 12, 2019 3:13 pm

There's really only a couple of possibilities here.

First being that if for some reason the #23 wire which tell's the transfer switch to transfer is grounded along the way, or the relay inside the generator is stuck in standby mode. You would be able to tell this by starting the generator in 'Manual' mode. If the switch instantly tries to transfer to standby you have a grounded 23 wire. It would also try to transfer when the unit exercised (which it should not do).

If the 23 wire is normal and un-grounded when it's supposed to be, then I would check to see if you have a loose wire in the transfer switch to the upper coil. The 2 coils in the switch rely on 240V power from either the utility source or generator source. The upper coil gets power from the utility, broken through the small ice cube relay inside the switch and then through a small limit switch right next to the coil. If either the coil, wiring, ice cube relay, or limit switch are faulty, you will have this scenario.

All of the things mentioned above can pretty easily be checked with a quality digital volt meter. The 23 wire and 194 wires will be 12V DC voltage, everything else will be 120/240V AC voltage.
Generac tech for over 12 years. I'm here to help!
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Verified Dealer
Verified Dealer
Posts: 35
Joined: Mon Nov 12, 2018 9:45 am
Location: Stockbridge/Chelsea, Michigan

Sun Jan 13, 2019 5:38 am

I agree with Chris on diagnostics, there is no logic in the transfer switch itself so pretty simple to trace wires and voltage. The most common issue I have seen is one of the wires on the top(utility) solenoid is disconnected. If all wiring is in place then it's time to get your VOM out and check out the limit switch and transfer relay(ice cube).
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