Hello, I recently upgraded my old Comfort Net thermostat to a Nest thermostat. In the process of doing so, I made sure my fan speed for cooling and heating where set to the correct settings, but I ran into a weird problem. The cooling and heating fan speeds are good, but I cannot find the dip switches for the fan-only mode. The Furnace manual shows them, but I cannot physically find them on the board anywhere! The reason why I'm asking about this is because when the fan-only mode is selected, the fan speed is so slow that it does not circulate enough air around the home.

This is the model Furnace I have:




These are all of the dip switches:




These are the settings in the manual:




Also here is the link to the full manual: Furnace Manual

Switch bank S5 just isn't anywhere on the board.
If anyone knows why this is and how I can fix it, please let me know. Poor air circulation in the house really sucks.

 

S5 is on the center of the board. But it has only 2 switches on it.

 

According to the diagram on page 58 of the manual S5 is under S4 except it looks like they may have removed two of the switches. The two switches under S4 are also labeled S5 in your picture.

On their website a new control board looks the same as your picture and is also missing two switches.

My thoughts are they may have updated the board, but not the manual maybe?!?

Does your unit have a diagram of the board in it somewhere? If so see if it matches the manual page.

Were there settings in the original thermostat for the fan? Since the original thermostat was able to actually communicate with the control board on top of providing the normal thermostat switching functions it makes me wonder if the fan speed was actually controlled by the thermostat and the manual was never updated to reflect it.

 

According to the diagram on page 58 of the manual S5 is under S4 except it looks like they may have removed two of the switches. The two switches under S4 are also labeled S5 in your picture.

On their website a new control board looks the same as your picture and is also missing two switches.

My thoughts are they may have updated the board, but not the manual maybe?!?

Does your unit have a diagram of the board in it somewhere? If so see if it matches the manual page.

Were there settings in the original thermostat for the fan? Since the original thermostat was able to actually communicate with the control board on top of providing the normal thermostat switching functions it makes me wonder if the fan speed was actually controlled by the thermostat and the manual was never updated to reflect it.

So the furnace has this chart for fan speeds on it:




Also, this diagram of the board which is mostly the high-voltage components:




And yes, I'm pretty sure the old thermostat did control the fan speeds.

On a side note, there are four other dip switches on the board. I'm not sure if they have anything to do with this because there is no mention of them in the manual and I have no clue what their labels imply:

 

And yes, I'm pretty sure the old thermostat did control the fan speeds.

On a side note, there are four other dip switches on the board. I'm not sure if they have anything to do with this because there is no mention of them in the manual and I have no clue what their labels imply:

I'll admit I'm not a HVAC person by any means, but more or less someone who is curious and I'm pretty confident in what I think I found.

Any settings you made with the old thermostat are probably stored in the thermostat itself and not on the control board. The nest thermostat won't be able to communicate with the control board the same way the original one thermostat did and so certain features will only work in a default or factory defined setting unless it can be changed by the switches.

Your image of the control board diagram in the furnace itself seems to be missing the fan speed switches as I was suspecting. When compared to the picture in the manual it seems that general area was drawn 180 degrees different and the switches are kind of labeled different. Other than that everything else looks the same. The replacement board I found online replaces several obsolete boards and they may have just left the switches off due to it not being common to all the units it is designed to work for (there was a pretty good list) and the functionality was added to the thermostat instead.

As far as the other switches go I really would have no idea. It's possible they are settings to affect how the microcontroller "reads" sensors like the flame sensor or induction blower sensor or whatever else (it's getting late and I can't put what I'm thinking in words), and maybe factory testing.

I wish I had better news, but I'm guessing without the original thermostat you are simply not going to be able to do what you want. Maybe someone else will stumble across this who knows more details and have better news.

Good luck