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Old 06-04-2009, 03:43 PM   #16
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HVAC system heat won't run with standby generator running...


Try switching out the Lennox control board that gives you the error code. It may be hypersensitive.

Otherwise you need the board schematic (you'll probably have to sign a non-disclosure agreement) and one of these
http://www.pctestinstruments.com/

These guys are stumped, but their troubleshooting method was by replacement. Since everything else was tried, I'd say it was a grounding problem.
I'd do the minimum grounding required for it work and debug this config. if necessary, and then cautiously build back up to an NEC ground system.

I'd love to tackle this one. . .maybe twice in my life I faced a problem like this.


Last edited by Yoyizit; 06-04-2009 at 03:55 PM.
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Old 06-04-2009, 04:15 PM   #17
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HVAC system heat won't run with standby generator running...


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Originally Posted by Billy_Bob View Post
You need an "online" true sine wave UPS. This makes electricity ALL the time whereas other UPS only make electricity when power is removed.

FYI here is what dirty power looks like...
http://www.jkovach.net/projects/powerquality/
I think that the Liebert UPS that is sitting my basement now is the same as what you mentioned above. The tech installing it got sine wave that looked like this also. PT

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Old 06-04-2009, 04:21 PM   #18
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HVAC system heat won't run with standby generator running...


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I think that the Liebert UPS that is sitting my basement now is the same as what you mentioned above. The tech installing it got sine wave that looked like this also. PT

You may need a storage scope because almost certainly you are looking for a transient. That's what logic analyzers do; capture the transient that caused the problem. In your case you may need one that runs on batteries so it is totally isolated from the AC line.
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Old 06-04-2009, 04:22 PM   #19
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HVAC system heat won't run with standby generator running...


"Dirty power" sounds like BS to me -- especially because they checked it with a scope and tried a Liebert double-conversion online UPS.

I don't know why they wouldn't try a new controller board before ripping out the entire system -- did they?

My only other thought is that there is something attached to the control computer (circ. pump, temp. sensor package, damper motor, etc) that is getting power from the mains panel and is not getting switched to generator along with everything else. That's unlikely, and even more unlikely that 2 contractors missed it, but possible.
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Old 06-04-2009, 04:44 PM   #20
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HVAC system heat won't run with standby generator running...


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"Dirty power" sounds like BS to me -- especially because they checked it with a scope and tried a Liebert double-conversion online UPS.

I don't know why they wouldn't try a new controller board before ripping out the entire system -- did they?

My only other thought is that there is something attached to the control computer (circ. pump, temp. sensor package, damper motor, etc) that is getting power from the mains panel and is not getting switched to generator along with everything else. That's unlikely, and even more unlikely that 2 contractors missed it, but possible.
Yes, they did put new computer controller board on the wall, the one with the flashing function lights, that didn't fix it either. You guys are starting to talk over my head on this! It would help if I was an EE. I'm going to call them tomorrow and see what they're going to do, since they are picking up the tab. BTW, this HVAC company is very large with about 50 employees, not one guy and a helper.

I appreciate everyones comments but my original question was...did anyone here know of a combination of generator/HVAC system that they KNOW works during a power outage? PT
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Old 06-04-2009, 04:51 PM   #21
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HVAC system heat won't run with standby generator running...


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.did anyone here know of a combination of generator/HVAC system that they KNOW works during a power outage?
This model has an almost 100% chance of starting up during a power outage...






Seriously though, if Lennox and Generac guys are telling you that your current setup should work, I dunno...
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Old 06-04-2009, 09:58 PM   #22
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HVAC system heat won't run with standby generator running...


I've installed a bunch of generators, though the smallest is around 50 KVA.

In my experience, most fancy electronic things (including UPSs) are very picky about their power supply. They want the voltage to be maintained within about 10% or so, even when starting a compressor. Very few generators can start a motor of any size without a considerable voltage dip.

They also want the frequency to be very close to 60 HZ. A lot of them will fail if the frequency gets below 59.5 HZ, or above 60.5. Unless there's an electronic governor on the gen, the frequency is likely somewhere between 55-65.

The older mechanical HVAC units had no problems with these power fluctuations, but the newer electronic ones won't tolerate it.

Rob
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Old 06-05-2009, 11:59 AM   #23
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HVAC system heat won't run with standby generator running...


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In my experience, most fancy electronic things (including UPSs) are very picky about their power supply.
They want the voltage to be maintained within about 10% or so, even when starting a compressor. Very few generators can start a motor of any size without a considerable voltage dip.

They also want the frequency to be very close to 60 HZ. A lot of them will fail if the frequency gets below 59.5 HZ, or above 60.5. Unless there's an electronic governor on the gen, the frequency is likely somewhere between 55-65.

The older mechanical HVAC units had no problems with these power fluctuations, but the newer electronic ones won't tolerate it.

Rob
OK, so the AND function which is giving the Power Bad signal has at least two inputs: RMS voltage and freq. I suppose with a generator you could have problems with both, on startup.
Maybe there is a factory setting for the control board that loosens the spec's for power quality.
To fix the generator's capability to handle transient loads probably would at least require a large flywheel.
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Old 06-05-2009, 12:18 PM   #24
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HVAC system heat won't run with standby generator running...


It may indeed be a frequency related problem. Maybe the fix is something like powering the control board with a small true sine inverter.
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Old 06-05-2009, 01:32 PM   #25
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HVAC system heat won't run with standby generator running...


I'm still not buying the dirty power reasoning.

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Then he bought a Liebert "true" UPS unit for computers, hooked it up and it didn't work either.
I gotta assume from that description that it was a double conversion, online, true sine wave UPS. There's no way that crap generator power would get past it. If the input power fell out of the UPS's spec range it would switch over to batteries. If it stayed on batteries for too long, it would shut down. The controller module would only see near-flawless power, or no power.
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Old 06-05-2009, 06:04 PM   #26
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HVAC system heat won't run with standby generator running...


make sure you have a solid ground wire from the generator to the furnace
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Old 06-05-2009, 11:36 PM   #27
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HVAC system heat won't run with standby generator running...


Actually not having "pure power" is a problem in the automotive area as well! They have had problems with A/C spikes wrecking the vehicle "programming" process.

When "programming" vehicles with new software, the process can take quite awhile and drain car batteries, so an external source of power is needed for the vehicle. But they are quite picky about the external power source being used to "jump" the car battery during programming...

http://www.ereleases.com/pr/midtroni...-hybrids-13474
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Old 06-06-2009, 09:42 AM   #28
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HVAC system heat won't run with standby generator running...


"Progress" is a myth.
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Old 06-26-2009, 08:09 PM   #29
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HVAC system heat won't run with standby generator running...


This is all very interesting, because I am having the same issue, that my A/C won't start when on my generator. With my case, the A/C and generator DID work together just fine before we got a new furnace installed. Now with the new furnace the A/C clatters the furnace control board relay and then trips its breaker, all while pulling the full-time blower down to a crawl speed.Having read this thread, the only solution seems to be to make a totally separate control circuit for running my A/C only when on the generator, completely outside any connection with the furnace controlller.Oddly, the furnace runs just fine on the generator. Just the opposite of this fellow's problem.
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Old 06-26-2009, 08:15 PM   #30
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HVAC system heat won't run with standby generator running...


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Originally Posted by Zoandar View Post
the A/C clatters the furnace control board relay and then trips its breaker, all while pulling the full-time blower down to a crawl speed.
This brings up another thought.

The control circuitry of the HVAC and the generator are probably quite sophisticated, which may result in each system trying to accommodate to the other, possibly resulting in "hunting." This you might see on a scope, briefly.

Each system works by itself in factory tests, but when hooked together they become underdamped. If the resulting oscillation grows without limit one or the other unit would shut down or be damaged. Substantially increasing the elec. load on the generator should change this pattern.
Generally you want "critical damping," where any oscillation quickly dies out.

The clattering system hung on for a while but the other one bailed out at the first sign of trouble.

With more and more HO generator systems this problem may start showing up in more places.


Last edited by Yoyizit; 06-26-2009 at 08:35 PM.
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