HVAC wiring help

[Dutch445]

Last year I installed a stoker coal stove to heat with, this year i ordered
a digital controller to use which gives me a thermostat upstairs to control
the feed rate, and fan speeds.
part of this controller is an outlet to control my furnace fan which we use to
circulate the warm air. (the coal stove has ductwork that ties into the
cold air run of the home's furnace)
i have run into a few issues with the furnace fan tie in.

the furnace thermostat is a Lux 500, programmable, and it also
controls the A/C.

if i remove the thermostat from the wall, and jump the R and G terminals,
i can simulate "fan only" and the furnace fan runs just as if i switched the thermostat switch
to "fan only". if it put the thermostat back in place,
and jump the same 2 wires in the furnace where the thermostat wires into the furnace,
the fan comes on, but, does not shut off instantly when the jumper is removed. somehow
the thermostat is changing the fan control while it's hooked up and we try to jump
and run fan only.
i'm not sure that i'm not causing a "heat" cycle to start, although the thermostat has been in the off position.

biggest question is about the thermostat and is there a way to engage "fan only"
while the thermostat is installed, without the delayed shut down of the fan, (about 90 seconds)

if i can't fix this, is it going to cause any issues with the furnace fan if it runs on and off as needed
when controlled by the coal stove controller? (they have installed a relay , and call it a dry connection)

 

[kenmac]

I'm better at it if I can see it. I'll try to answer as if I can see what you're talking about. Yes, you should be able to turn the fan on, but I'm not sure about this controller that you are trying to use. I would run power from this controller to a relay . When energized ,the relay would power a wire that would send power to the green wire (If that is the wire you choose to use) inside the furnace. The green wire is usually wired to bring in the high speed fan . Usually used for cooling. Is this close to what you are trying to do ? u may also be able to use 1 of he fan speeds. If your furnace is the type with a 3 speed motor, You could use 1 of the speeds not in use. Again, use relay , From the controller run a wire to a relay to bring in 1 of the speeds on the fan not in use

 

[Dutch445]

thank you, yes, this controller is just a relay closing the contacts as the thermostat would do, and right now i am using
R and G wires, works ok , better if i remove the original furnace thermostat from the wall. no different speeds are being
used that i know of. (maybe?)
i'm just hung up on why with the original thermostat connected i get a delayed shutdown of the fan, where if i take
that out of the system the fan is instant on and instant off like the "fan only" switch does.

thanks

 

[kenmac]

i'm just hung up on why with the original thermostat connected i get a delayed shutdown of the fan, where if i take
that out of the system the fan is instant on and instant off like the "fan only" switch does.

thanks

I'm just guessing cause I don't know your system . It could be going through a delay
In the t stat or a time delay relay within the unit circuit board.time delay relays for fan on and off are used by most of the system manufactures

 

[Dutch445]

i contacted the thermostat manufacturer Lux, and their response was that my
particular thermostat would have no bearing on this, it's just basically switches,
so the delay must come from the furnace control. i can live with it, it's just
not working the way i thought it would.

 

[kenmac]

I didn't know about your t stat. Like I said some have a built in delay even for the a c compressor to start. But, most (if not all) heat units have the time delay relay for the fan to turn off. This is to remove as much heat as possible b4 shutting down. Like I said in a preious post. You don't have to o use the green wire connection,you could add a relay to bring in the fan on another speed. This other speed could be /would be instant on and instant off

 

[Dutch445]

looks like my furnace uses 1 speed for heat, another for cool,, and the third not used.
here's a pic from the back of the door, sorry if it isn't easy to see:

 

[Loadstar]

I would agree with what Lux says about the thermostat. Most are just a switch as they said. I would suggest simply landing on your R and G terminal in the furnace. I'm not fully understanding what your problem was, but I believe you are saying when jumped at the furnace the blower stays on an additional 90 seconds after jumper off?

 

[Dutch445]

yes, but only while the thermostat is connected to the wall plugs upstairs..
if the tstat is pulled off the wall, then everything works as i expect.

 

[Loadstar]

Well then that's more than likely doing it. Not really a problem is it?

 

[Dutch445]

i have to look more on how it affects the furnace coming on.,
example would be power goes out, coal stove goes out, nobody home,
and power comes back on , would it affect furnace from coming in
properly. it seemed last week while running the fan the furnace didn't fire.
but i didn't really commit the time needed to verify that as i had some other
things going on at the time.
i'll dig into it this weekend when i have some time to concentrate.
thanks

 

[PILOON]

Just a shot in the dark, but is it possible that there is a 'run on' type circuit thermostatically regulated to provide a cool down period?

 

[Loadstar]

I really don't feel you would have an issue jumping off G. Jump g out at the furnace then shift stat over to heat and see how it does. You could also pull stat off and jump R,W,and G in furnace and see how it does. I don't think there will be an issue.

 

[kenmac]

looks like my furnace uses 1 speed for heat, another for cool,, and the third not used.
here's a pic from the back of the door, sorry if it isn't easy to see:
View attachment 397311

OK, so what u want to do ? You probably have high, med. And low speed.. low speed red, med speed blue, high speed black. High speed usually for cooling,, low speed/ med speed heat.

 

[Coyote machine]

I wouldn't worry about it at all. The furnace wants to extract as much heat as possible from itself for efficiency AND to protect the furnace heat exchanger and other critical components from premature failure. High heat is OK when it's running, not when it's sitting still. Don't defeat the delay, JMHO.

 

[murphy1244]

CM says "I wouldn't worry about it at all. The furnace wants to extract as much heat as possible from itself for efficiency":thumbsup:

That's it exactly. Nothing to do with protecting the exchanger thou.

 

[Coyote machine]

Why you say, 'nothing to do with protecting the heat exchanger'?

 

[murphy1244]

Why you say, 'nothing to do with protecting the heat exchanger'?

Not that fan cycle CM. They have done without out that cycle if it was a less than 80% furnace

 

[yelbike]

Try a different stat. I don't like brand bashing but in my line of work use only Honeywell or white Rodgers. I prefer Honeywell BC of their awesome and quick tech support. Now back to our regular scheduled event.

I really don't see the with the delayed shut down. Its actually a desired feature in this case that you scavenge more heat from your auxiliary heat source.

BTW cm, the heat exchanger is in no way in harms way. Generally they are capable of operating normally near 170f, there no way an auxiliary furnace will have that output if it's in the return duct. Keep in mind I have not seen the installation, so it's an ASSumption.

 

[Loadstar]

Try a different stat. I don't like brand bashing but in my line of work use only Honeywell or white Rodgers. I prefer Honeywell BC of their awesome and quick tech support. Now back to our regular scheduled event.

I really don't see the with the delayed shut down. Its actually a desired feature in this case that you scavenge more heat from your auxiliary heat source.

BTW cm, the heat exchanger is in no way in harms way. Generally they are capable of operating normally near 170f, there no way an auxiliary furnace will have that output if it's in the return duct. Keep in mind I have not seen the installation, so it's an ASSumption.

I second honeywell stats. Especially their simple models such as a TH5220D1029. Coal miners can beat on them, elderly can figure them out and they are versatile.
I keep recommending hooking up on the low voltage strip because that is where your board is waiting for inputs and how it "knows" what is going on. You will have to get much more complex within the furnace if you take a different path.