Questions on Generac 6852 setup with Lightning

[bmwhitetx]

With the Generac switched to Generator power, the following happens

1. IF I turn on the home fans manually, those run
2. About 80% of the time, the furnace fans don't turn on. 20% of the time, they turn on for a second, then shut down.
3. If I don't manually turn on the home fans, those stay silent (furnace isn't running)

Furnaces go through a start-up sequence. The furnace fan you mention is a small draft fan which uses very little power. Once on and the controller senses the draft (pressure switch), then the igniter will heat up and the gas valve opens turning on flame. Another sensor registers the flame is on (If not then shuts down). House fan turns on many seconds later.

If any of this fails it will give an error code. What code is the furnace giving you? It's typically a series of blinks (fast/slow) on the onboard controller LED.

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[CyclopsThere]

Furnaces go through a start-up sequence. The furnace fan you mention is a small draft fan which uses very little power. Once on and the controller senses the draft (pressure switch), then the igniter will heat up and the gas valve opens turning on flame. Another sensor registers the flame is on (If not then shuts down). House fan turns on many seconds later.

If any of this fails it will give an error code. What code is the furnace giving you? It's typically a series of blinks (fast/slow) on the onboard controller LED.

I opened up the panel where the draft fan is, but saw no LEDs on anything. Wonder if it hides in a different spot on this model. I'll try to track that down this weekend.

Electricians will be back out next week to take a look

 

[bmwhitetx]

I opened up the panel where the draft fan is, but saw no LEDs on anything. Wonder if it hides in a different spot on this model. I'll try to track that down this weekend.

Electricians will be back out next week to take a look

The LED won't be in that panel, it's on the controller board. On the panel next to that one there will be small sight glass. If you look through that little window you should see the LED. It should be continuous on for normal operation.

Note anytime you have that panel off where the draft fan/gas furnace is, the power is cut to the entire unit (there is a door switch). If you put the panel back on while the t-stat is calling for heat you may get a lockout for a minute or two.

This reminds me that in your fail-over sequence, when you turn on the breaker to the unit, that is equivalent to putting that door panel back on. The unit may have a lockout for a couple of minutes where only the blower fan will run.

So maybe make sure t-stat is not calling for heat and fan on Auto. Power up unit via breaker, wait three minutes, then turn t-stat to call for heat. I don't how this works with a Nest. Unless it has a battery backup, it is losing power along with the furnace (most WiFi t-stats get power from the furnace control board via the "C" wire).

 

[CyclopsThere]

Will try this tonight, thanks so much for the explanations. Saved off that PDF as well.

 

[CyclopsThere]

I don't how this works with a Nest. Unless it has a battery backup, it is losing power along with the furnace (most WiFi t-stats get power from the furnace control board via the "C" wire).

Oh yes the nest has been interesting. It does have a battery in it but I'm not sure what exactly for, I assume so it doesn't lose ROM or clock or something.

Breaker to the furnace off, the nest reads "Power Out" or something similar. Breaker on, nest begins working normally. This is no matter which power source I'm switched to.

 

[bmwhitetx]

Oh yes the nest has been interesting. It does have a battery in it but I'm not sure what exactly for, I assume so it doesn't lose ROM or clock or something.

Breaker to the furnace off, the nest reads "Power Out" or something similar. Breaker on, nest begins working normally. This is no matter which power source I'm switched to.

Yeah, t-stat's and furnaces should just work after a power failure/restore (which is what you are doing). But there may be some delays/lockouts that are causing some of your perceived "erratic" behavior. Take it slow and notice the LED (hopefully it's not it an attic like mine and a pain to get to).

 

[CyclopsThere]

dirt crawlspace where i can crouch walk. bit of pain but not much. thanks again for the suggestions. counting down minutes til i go home and try some of this stuff out

 

[carys98]

I had a Trane like yours until recently (had to replace it this winter) and have successfully powered it with the truck and the Generac panel so it definitely can work. The only difference is that I have Ecobee thermostats.

 

[GDN]

Oh yes the nest has been interesting. It does have a battery in it but I'm not sure what exactly for, I assume so it doesn't lose ROM or clock or something.

Breaker to the furnace off, the nest reads "Power Out" or something similar. Breaker on, nest begins working normally. This is no matter which power source I'm switched to.

@bmwhitetx is giving some good things to try. On the nest - it does sound like it is getting power from the furnace (this is standard), but not all of them do. It all depends on how it is wired. Your thermostat is telling you though that it lost power when the furnace did. When you connect to the truck to the sub panel and power it up - that thermostat should get power again immediately.

There is a very very slight chance it could have a different power source, but doubtful. The battery is just for backup.

 

[CyclopsThere]

I had a Trane like yours until recently (had to replace it this winter) and have successfully powered it with the truck and the Generac panel so it definitely can work. The only difference is that I have Ecobee thermostats.

Did your Trane have a little viewport to see error lights in it?!?!? Mine doesn't I swear.

 

[carys98]

Did your Trane have a little viewport to see error lights in it?!?!? Mine doesn't I swear.

I don’t remember to be honest. I did see the LEDs with the cover off. My installers did not connect the thermostat correctly so I had to open it up and rewire it to get the two stage to work right. If you remove the cover and see the controller board you should be able to override the switch and get it to turn on with the cover off.

 

[EVpower]

There might be an issue with the furnace flame sensor. Some gas furnaces run a very small current through the burner or pilot flame to the gas pipe to confirm the flame. There needs to be a path from the gas pipe to the power source neutral/ground bond to complete the flame prove out circuit.
This has been a problem with portable generator connections where the generator ground/neutral is not connected to home grounding system.

Steve

 

[CyclopsThere]

There might be an issue with the furnace flame sensor. Some gas furnaces run a very small current through the burner or pilot flame to the gas pipe to confirm the flame. There needs to be a path from the gas pipe to the power source neutral/ground bond to complete the flame prove out circuit.
This has been a problem with portable generator connections where the generator ground/neutral is not connected to home grounding system.

Steve

Sent this on to the electricians who show up tomorrow to tie things up. Fingers crossed! Thanks

 

[CyclopsThere]

OK we're up and running, furnace is firing. Very happy with the electricians who dealt with a very unique situation and stuck with it. Inspector comes up next and once that's done assuming we pass inspection, I'll start to look for phase 2 circuits to wire up to the generac. The gas heater pulls relatively little current so we have capacity if we want it.

 

[GDN]

OK we're up and running, furnace is firing. Very happy with the electricians who dealt with a very unique situation and stuck with it. Inspector comes up next and once that's done assuming we pass inspection, I'll start to look for phase 2 circuits to wire up to the generac. The gas heater pulls relatively little current so we have capacity if we want it.

Wait - you can't just leave us hanging like that. What was the issue?

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