Hi,
I developed a new thermostat and i need the schematic for one of the lennox furnace
I put the model i have in the house but can be any of the newer models
I need the schematic of the main board, not the installation wiring diagram.
I know it is a common wire from furnace going to thermostat and 3 wires returning to thermostat
I need to know if the wire going to thermostat is AC or DC and voltage ( i assume is 24 VAC)
Most important is to know what electronic component get the return wire connected to , rectifier, relay, transistors, or what
I intend to replace the existing relays , like my home thermostat- Honeywell, with some mosfet transistors, but i have to see what is connected on the board to that return wire
Also, for fun, is connected directly the motor or what, and what is the current going through these wires
Thank you
Ion

 

This is the diagram. I can't help you with the rest of your list.

 

Thank you.
I am sorry, but maybe i did not express my self clear
I have from Lennox the installation manual and on page 38 is your reply
What i am looking for is the schematic of the PCB control board sshowing in the attached
The one with all the surface mount components and electronic on it

 

I doubt that you will get the information that you are looking for on any site.
You can try contacting Lennox but I am confident that they will not give you this information.

 

In fact any furnace control board will do the job
Or if somebody has a control board , it could take a close look up picture of front and back
I can see then the components
Thanks any way for support

 

You will not find that information. That is patented and proprietary information.

24vac is used for switching. The R terminal is the 24v source to the thermostat.
The W, Y, G terminals are the 24v returning to the furnace for control.

C (common) is only sent to the thermostat if it has a clock circuit or WiFi transmitter.
The C wire is not required for switching purposes.

P.S. You are designing a new thermostat..... how does that become URGENT ?

 

I finished and tested everything and i need to make the final PCB, then the plastic box
I will have the opportunity to show it to Wall mart as it is very cheap - 15 dollars manufacturing cost with all the features of the top of the line Honeywell
But they use latching relays, very expensive 6-7 dollar a piece, so the cost is ruined
My goal limit on price is 20-25 dollars. Similar from Honeywell are sold 150-175 dollars

 

Designing a product is just one step. When/if you get to the point your idea goes into production you need to have made sure that you are not infringing on anyone's patented ideas.

Companies like Honeywell hold most of the patents on temperature control systems and don't take kindly if their patented processes appear in non authorized products.

Good luck in your endeavors and let us know how you make out.

 

i do not infringe anybody patent as it is only one microprocessor and the rest is software -mine
No other hardware.
And if using a thermistor to read the temperature is patented, then 99% of the thermostat manufacturers should be sued
They use latching relay to interface, i use mosfets

 

You would be surprised at what gets patented: https://nest.com/ca/press/nest-count...-infringement/

 

It is like apple or others putting troll patents
Patents never developed , but stay there just in case
Take the telephone for example.
Graham Bell (RIP) and family should be multi billionaires by now.
Crazy world ((((((((((((((((((((

 

Perhaps I missed something ---- you have a furnace to get the information you're looking for.

You have a control board on your furnace. You should be able to analyze the circuitry on that board. You should also be able to measure the current from the motor.

 

I just removed from the furnace
A schematic is also better
And guess what ... the controller board is made by .... drums .......... Honeywell
Why I am not surprise ...
I see in the inputs few resistors in parallel than after is a voltage divider and which feed a diode and a cap in parallel. C ap probably for filtering the dc
The rest i do not care

 

If you're referring to the t-stat terminal connections, C is common to power the t-stat or connect a contactor/relay for a/c or accessories. (R is power/hot, C is the other side of the circuit)

Newer boards are microprocessor controlled, but the older ones are simpler I believe -> relays, circuitry for sequencing but no cpu.

G61v was a higher end furnace.

For example:

BCC3 - lennox G20, G26, etc...



carrier 2-stage:


Big difference, eh?

 

Stiil perplexed here.

You've designed a thermostat without knowing the basic fundamentals of the interaction between it and HVAC equipment --- sounds like the cart before the horse.

You also have a working furnace available to provide all the information you need.


The design of the controller board on a furnace is really not relavent to a thermostat.

All the electrical/electronic components within the furnace are simply for it's operation. The major function of the electronic controll board is to initilize a sequence of turning on & off devices while monitoring a series of interlocks. The methodology and sophistication will vary between models and types of equipment and maufacturers.

Now, regardless as how basic or sophisticated the HVAC equipment they are *dumb* devives. They rely on an input signal to tell the equipment as to what function to perform .

It's pretty much a standard where 24VAC is used for many components in the HVAC. This low voltage is derived from a line voltage to 24 VAC stepdown transformer.

The terminal connections for I/O is based on 24VAC



A thermostat's function is to simply provide the HVAC equipment with a input signal --- that's it.
How simple or sophisticated the thermostat is unimportant. The HVAC equipment doesn't care if a thermostat is using a PID controller with sophisticated and complex algorithims or a simple on/off funtion.
The thermostat provides that 24VAC signal via an internal switched closure interconnected to the HVAC by wire ( or a wireless signal ).

Bottom line is the HVAC is looking for a 24 VAC signal on a particular input terminal. Whether by manually applying a signal with a jumper or from an external remote device like a thermostat doesn't matter.