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Generac Guardian Gen 8kw Starts, Runs, Shuts down Then Restarts

James A. B.

Registered
Generac Guardian Standby Generator
(model)item#:0041094, s/n:35254444,volts:120/240, amps:66.6/33.3, watts:8000
My Generac generator (when rocker switch is set to manual) starts, runs for maybe 10 seconds then shuts down, restarts (on it's own) and shuts down again in lesser time. These are the same symptoms as if the High Temperature Sensor would be faulty. History- I have had trouble with the Low Oil Pressure Sensor, the High Temperature Sensor and the main Regulator from the propane tank.
These problems occurred in a short period of time, couple months each and after each issue the generator worked fine after faulty part replacement. My current problem has the same symptoms as if the High Temperature Sensor is bad but there are there aren't any Fault LED's lit. When the ambient temperature would get hot enough the generator would stay running as if there isn't any problems. I have connected a Water Column Gauge to the demand regulator (internal regulator thats connects to the carburetor) and the Gauge reads 11.5" to 12" Water Column which is the proper pressure. For fuel I use a 7 gallon propane tank and have been using that size tank for 8 years without any problems. I have researched this problem through the internet and have not found any answers or anybody else having this problem. It definitley has me baffled and I would truly appreciate anybodys input. Thanks
 

Birken Vogt

Registered
Is it putting out voltage during the short time it runs? Some of these will shut down if they don't see voltage output and restart in hopes of exciting the field again.
 

James A. B.

Registered
Hi Birken,
I finally had a cool temperature morning recently in the high desert of SoCal and tested the AC after starting the generator and it was putting out 124 volts AC. But what baffled me (again) is the generator didn't shut down like it has been in cooler temperatures. I just don't understand WHY! Thanks for the input. I will be testing the AC output everytime I start the generator until the time it will shut down to get your question answered. Thanks again.
 

James A. B.

Registered
Hi Birken,
I recently had my generator shutting down again and tested the AC voltage and it appears I'm getting the excitation voltage of 15.7 AC volts. Is it my understanding that if I'm getting the excitation voltage then the voltage regulator is supposed to kick in and produce the 120/240 voltage? If so would you happen to have any idea what in the voltage regulator would work on hot but not cooler temperatures?
 

Birken Vogt

Registered
Put 12 volts momentarily to the wire with the printed number 4 on the voltage regulator (while running) and see if it "takes off" and starts making 120 volts.
 

James A. B.

Registered
Hi Birkin, I tested my Generac Guardian generator today using a service manual that belongs to newer Generac models. I did the test 4 - Fixed Exitation Test/ Rotor Amp Draw Test which had me test the voltage regulator related to your suggestion. The 1st test was to remove wire 4 from voltage regulator and connect jumper wire from 4 to wire 15 the 12 volt fused battery supply and remove wires 2 and 6 from voltage regulator and connect multimeter test probes to test the AC voltage output. The AC voltage output was 87Vac. 2nd test Reconnect wire 2 and 6 then disconnect wires 11 and 22 and put test probes on these wires and record the AC voltage also. The reading on these wires showed 80Vac, reconnect wires 11 and 22. 3rd and 4th test was to set multimeter to DC amps remove jumper from wires 4 and 15 and connect one probe to wire 15 and other probe to already disconnected wire 4 and record static rotor amp draw and running rotor amp draw. The static rotor amp draw was 0.705A and the running rotor amp draw was 0.650A. Reconnect everything. The problem I'm having is Test 4 results chart are for the newer models which have different specifications/readings than my model. I also wanted to mention that taking the wires off the voltage regulator I had noticed a bluish color residue on the majority of the voltage regulator male pins and female connectors. They cleaned up easily and it wasn't very hot today and the generator didn't shut down. That residue might have been the problem I won't know for sure until the weather gets cooler. I tried getting my model rotor amp test specifications but not succeeding. Would you or anyone else might have an idea where I can get a service manual for Generac Guardian generator model/ item # 004109-4. Thank you again for all your help. James
 

Birken Vogt

Registered
I have done that test in the past but too complicated to follow over this forum format.

Do I understand it makes voltage sometimes and doesn't other times?

In any case, these old units are known for doing this sort of mischief and consider how much you want to pour into it before committing too much.
 

James A. B.

Registered
Yes, that was my problem. Started, ran for 10 seconds, shuts down then restarts and shuts down again. When it did that I was getting 17.4 Vac at the output which I assume is the excitation voltage for the voltage regulator. Now after cleaning the connections, during the Test 4 I mentioned, on the voltage regulator and connecting wires I have not had a problem of the generator shutting down. I ran it again this morning with no problems. The biggest mystery I would like to have a logical answer for (if cleaning voltage regulator hookups is a 100% fix) is why would it run without any problems during hot weather. SMH
 

radiodoc

Subscriber
Last Subscription Date
02/04/2021
Just a wild guess but perhaps the contraction of the metal in the contacts when cooler and the blue residue was creating a high resistance in the connection...:shrug:
 

Rupe53

Registered
Before you get too far reading between the lines I have to say that sounds like a classic case of a bad oil pressure switch. After 5 - 6 attempts at starting it will probably lock out and show a fault if it's new enough to have the idiot lights. If it's the older version it will just quit trying to restart. Of course you should take an OP reading as long as the switch is out. Should be 45 - 55 PSI cold.

BTW, if you pull one wire off the temp switch that will verify it's not the problem. (shorts to ground hot) You can also start the engine and pull the wire from the OP switch (after it starts) to see if it keeps running, but at that age I would check the pressure with a gauge anyway.
 

dacflyer

Registered
That blue residue sounds like classic copper corrosion..
Humidity might also be playing into things ( causing the corrosion ) Some vaseline usually helps give it a protective barrier against moisture.
 
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