HVAC system heat won't run with standby generator running...

Zoandar

Looks like a good place for one of those old round Honeywell thermostats and a separate 24 V supply, taking the furnace's A/C controller out of the picture.

wirenut1110

I realize this post is a little old but here goes anyway.

If you have the model 5416 18 KW generator, and you think it's a frequency issue, you can adjust this by the potentiometer on your voltage regulator board. Refer to your owners manual section 2.7 and it will explain how to do this. Voltage and frequency are directly proportional (2-1 ratio) so if your generator output voltage is 124 volts then the frequency is 62 Hz.

If you don't feel comfortable doing this go to http://generac.com and locate an authorized dealer in your area.

If you don't have an owner's manual, here's one for you Model 5416 18 KW give it time to load, it takes a while on my computer.

An added note, your generator does have an electronic governor.

Yoyizit

The manual posted above does give a clue to how tight the freq. is controlled. If no load gives 62 Hz you could infer that full load gives 58 Hz. If your furnace is looking for 60 Hz within a tighter tolerance than +/- 1 or 2 Hz, either on a steady-state basis or a transient basis, it won't get along with this generator.

I think the transient response (step response) of the generator is important in this application, and it's not given.
I'm looking for a generator spec'n like
http://www.expertune.com/images/ArtCharactFig4.gif
or
http://en.wikipedia.org/wiki/File:Hi...s_figure_1.png
except the horizontal scale would be time in milliseconds or tenths of a second and the vertical scale would be freq. or voltage, and the graph would show temporary deviations from the steady-state values.

The generator people might be able to advise you on what loads are likely to cause generator instability.

PTighe

Thanks wire nut 1110 but I'm not an electrician. This Wednesday July 1st, the HVAC Service Manager and his lead Tech will meet out here with a different Electrician they hired for a second opinion. He also is an authorized Generac dealer who is certified to work on these units. He will test everything on the generator while on the phone with the Generac Factory Tech advisor.

If something doesn't pass with the testing, Generac will send a Factory tech to my place with the guys above and check out himself. I have no say in this at all as the Dealer is handling everything now at his expense. All I can say at this point is that this exercise is getting pretty old. (Since January).

I have also heard though from the Dealer that on May 27th, Lennox issued a service bulletin to all of their dealers...that from now on, Lennox will not guarantee any of their products to work when used in conjunction with any standby generator. This doesn't make any sense though since Lennox has their own brand of generators that have the Lennox name on it but are actually manufactured by Generac. Go figure. PT

Yoyizit

That's the problem; each unit by itself meets factory specs. It's when they play together the problem shows up.
If the clues point to costly redesigns of HVAC & Gen control circuitry the people pursuing the problem will suddenly be struck blind, deaf and mute. It's called "aggressive disinterest."

Zoandar

I am not an electrician either, but I'll bet the entire issue lies in the design of the controller board depending upon what some caprice engineer ass-umed to be a "constant" in regard to line voltage and frequency, and it uses those values to compute some essential function, instead of adding in the circuitry it would need to calculate those values on its own. (To save a few pennies, no doubt.) The generator power "changes" the constants, so the system can't work.

I agree with the aggressive disinterest theory. And I find it particularly interesting to read of Lennox's tech bulletin release. Clearly they are setting up a loop-hole for any future issues of a similar nature instead of simply FIXING their flawed design so it can work with "imperfect" generator power.

So when was Generac's service bulletin released so as not to guarantee their generators will work with HVAC?

Yoyizit

I think this interaction problem will come up more and more as everything gets more complex.

Some GFCIs don't get along with some motor loads, some AFCIs don't get along if there is a radio station nearby, etc. . . .

And don't forget the recent example we all have had about drug interactions.

PTighe

I agree but I don't think it would cost "pennies" for Lennox to redesign their product, more like $$millions. This probably won't happen unless there is a class action lawsuit, so I'm not holding my breath.

To my knowledge, Generac has never issued any service bulletins, it was Lennox only. The service manager from the HVAC company said he would bring me a copy of the Lennox tech bulletin when he comes out here on Tuesday.

wirenut1110

I checked Generac's dealer website this morning and saw no service bulletins, and I doubt there will be any.

PTighe

Exactly, I wish I still had my old LOW tech Lennox system back if I had known this fiasco was going to happen. The bottom line is the Generac works flawlessly in a power outage. All the lights come back on in the house; the hot water heater and the well pump work, along with the freezer and refrigerator, the garage door openers....everything except the furnace.

Yoyizit

This is why I try to get appliances with electromechanical timers and no electronics.
Maybe vacuum tubes, which were inherently hardy, will make a comeback.

PTighe

Here is the Lennox Tech Service Bulletin they gave me shortly after I found out there was a problem back in January FWIW...

wirenut1110

It looks more like a ground issue than a frequency issue. Can you post a picture of inside the transfer switch.

I'm assuming you bought the pre-packaged 18 kw that came with a 200 amp SE rated switch.

P.S. I have a feeling something wasn't done when this switch was installed and a picture would confirm or deny this.

PTighe

This system has about 3 separate grounds installed by my electrician in accordance with the bulletin above. Yes, they took it right out of the box. Pics below, this is the best I can do. PT

wirenut1110

Okay thanks, it wasn't what I was thinking because I thought you may have had the service rated transfer switch that came pre-packaged with that model.