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Hank F.
Hank F., Technician
Category: Small Engine
Satisfied Customers: 15263
Experience:  Certified on Onan and Generac generators
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Have a 12kw whole house generator. will start and run 20

Customer Question

have a 12kw whole house generator. will start and run for about 20 sec. then shut down.
Then will start again run same amount then shut down. Keeps repeating cycle. Had propane regulator checked by gas co. perfect pressure. No indicator light com on.
Air filter is clean, oil level is good. What next?
Submitted: 1 year ago.
Category: Small Engine
Expert:  Hank F. replied 1 year ago.

What is the serial number of the genset?

Customer: replied 1 year ago.
Generac Model(###) ###-#### ***** (###) ###-####
Expert:  Hank F. replied 1 year ago.

It is odd that no warning lights are coming on, but it is possible that a light is burned out.

The first thing you need to do is to bypass either the LOPS (low oil pressure switch), or the HTS (high temperature switch). See if the genset will run for more than the 20 seconds.

If so, that system is at fault.

If it still shuts down, reconnect that circuit, and bypass the other one and test run again.

If neither of those determine the problem, we will have to dig deeper.

Customer: replied 1 year ago.
Bypassed both lops & hts still same resaults will start run 20 secs shut down and repeat
Customer: replied 1 year ago.
Also want to add that when trying an auto exercize all lights on the controll panel due light
Expert:  Hank F. replied 1 year ago.


The next thing is to get voltage and frequency readings from the unit while it is running for those 20 seconds.

How much voltage is being produced, and at what frequency?

Customer: replied 1 year ago.
how do I take your sugested readings and where. Are you talking about the generator out put? what does that have to do with engine shut off??? when i bypassed the htps engine would not even start, wouldnt turn over. Do you have an actual Generac Teck in your group????
Expert:  Hank F. replied 1 year ago.

I am a certified Generac technician, and have been for 15 years.

You stated in your last reply, and I quote, "Bypassed both lops & hts still same resaults will start run 20 secs shut down and repeat "

Now you say it wouldn't start, and wouldn't even crank. Which is it?

How did you bypass the switches?

Customer: replied 1 year ago.
LOPS removed two screws from switch put the two wires together with a screw. Started genset both manually and auto mode.
Engine ran Aprox 20 sec and shut down . Aprox 5 sec later genset would star again run less than 20 sec and shut down.
Reatached wires to LOPS.
HTS removed two wires from switch,used single wire with two spade ends to connect the wires together. Tried to start genset high temp indicator came on genset would not turn over. Both manually or auto mode. Reconnected wires to HTS
Expert:  Hank F. replied 1 year ago.

That is not how to bypass the LOPS and HTS. To bypass them, you disconnect the wires and tape them off so they can't touch anything. These are both NO switches.

Customer: replied 1 year ago.
Ok one at a time, i discounected first the LOPS taped ends started genset same issue. I reconnected the LOPS and disconnected the HTS taped ends started genset same issue. sorry for the delay to respond but work untill 6pm then work on this thing
Expert:  Hank F. replied 1 year ago.

Ok, get the voltage and frequency readings. Lets make sure the power is not the problem.

Customer: replied 1 year ago.
where due I take these readings at the junction box before it goes to the transfer switch. Its a small box I have a red& Black wire in a block the goes to the transfer/breaker panel that attaches to my main breaker panel
Expert:  Hank F. replied 1 year ago.

The best place to get the readings is directly at the circuit breaker on the genset, with the breaker turned off to eliminate any outside interference.

Customer: replied 1 year ago.
sorry for this delay Just got to start the gen with breaker shut off. started gen my reader set on 600V my reader was .10
at the power to the breaker.
Expert:  Hank F. replied 1 year ago.

OK, if you have no power coming from the genset, you need to do a test called the Fixed excitation/Rotor amp draw test.

Click here to download the procedure.

Let me know the results.