We have an older (1989) Lennox NG furnace, model # G16RQ3-50-7 Serial # 5889A01168. According to the documentation I have, there are four possible settings for the blower motor speed, all of which are controlled by how motor leads are wired. These leads are found in the blower junction box. I'd like to know which setting mine's set at currently and if it's not set to high, how to rewire the leads to make it so. I've attached a picture of the leads are they currently are in the junction box. Please let me know if you need additional information or pics and thanks for your help with this.

 

Welcome to the forums.

Please confirm for me that the wires coming in the right side of the box are from the furnace and the ones on the left are to the blower motor.

Please list the colors on both sides.
It looks like red, black and white from the furnace.
It looks like red, black, yellow and white from the motor.

Typically the colors are....
white = neutral
red = low
yellow = medium
black = high speed.

As a guess...... you are using black for A/C and red for the furnace.

I only see three speed colors. I see brown which is usually for a capacitor.

 

Thanks for taking time to respond to my question and for your help with this.

Here's the additional information you requested:

Yes, the wires on the left side are to the blower motor while those on the right come from the furnace.

The wire colors to the blower motor are Black, Red, Yellow and White.
The wires from the furnace are Black, Red, Yellow, White and Brown

Connections within the box (where "in" means from the furnace and "out" means to the blower motor):
Black (in) to Black (out)
Red (in) and Brown (out)
White (in) to White (out)
Red (out) and Yellow (out) not connected to anything.

Hope this is the info you need.

Thanks again

BTW: we don't have A/C so I'm not sure what function(s) are served by the the black to black connection.

 

That would be backwards.... or is brown a motor color.

It looks like you're currently set up for high speed operation.

 

That's good news if it's on High. This is what I'd like it to be.

Re: the red (in) wire: From the documentation I have, it appears the red (in) comes from what looks to be a fan control switch (?) and is connected to the brown (out) in the box. The brown then heads off to the blower moter area where it may end up being routed to the blower motor capacitor. Or something like this.

Hope this makes some sense.

 

You have documentation. It would be helpful if you take a picture and post it.
Check the following link and see if it's the same wiring. (figure 17)
See if figure 15 matches your control board.
Manual

 

Here's the documentation I have -- at least a few selected pages.

 

Let's try this again. The first attempt failed because it exceeded file size limits. Here goes...

 

This one should be easier to read.

 

Ok..... I highlighted the area of interest. I'm fairly certain the black to black connection is for cooling and the red to brown is for heating. So..... your high speed is set for cooling and your heat is medium high. Since you don't have A/C...... you can switch the two and your heat will be on max.

 

That's interesting because we don't have A/C.
According to the speed chart, brown is the medium high blower speed.

I've emailed you the speed chart.

 

You don't have A/C but the furnace is prewired for it. Cooling is automatically the highest speed. Your furnace was delivered to you with the heat on the red wire. Someone has already increased the speed to the brown tap. Sounds like you have an airflow issue there. Possibly undersized return ducting.

 

Thanks for your help with this. I'll make the adjustment later today. Hopefully we can keep this furnace going for a few more years. When we moved in 4 months ago, the air flow from the furnace was practically nill until I discovered that two of the 15 6" flexible air ducts that supply heat to 1st floor registers were disconnected. As a result, we were blowing air into the crawl space. Replacing those helped alot but more work needs to be done with the rest of them as they're original equipment. And none of the metal to metal connections in the system were sealed. They are now. It's been interesting trying to understand the intended vs actual air flow patterns in this house. And from what little I've learned so far, I can understand why the change was made to the blower motor's factory setting. The change I'm going to make may help a little but really does not address root cause. For the time being, however....

Thanks again for your help.