The furnace came with the house when I bought it in 2015. It's worked but always had a noisy transformer and occasionally the burners wouldn't light and the blower motor would just blow cold air until I shut it off and started it back up again.

This year I have been having a problem with the blower motor intermittently not wanting to start up either in auto or manual mode. It will start up eventually, but is slow to do so and if I run in auto mode the unit will cycle on and off multiple times before reaching the thermostat temp.

In trying to understand the problem, I've done some research on the Trane XL80 and realized that while the box and some of the hardware is original, it is missing the control board and instead has a Honeywell s8910u hot surface ignition as the main electronics. It is essentially running as an inefficient, single stage one speed system instead of an efficient, two stage, 4 speed system.

I have ordered a new A.O Smith F48N78A01 motor (same as what is in there now) and will replace the capacitor as well as I expect one or both of them are the issue.

My question is should I try and return it to a more efficient system or leave it as is? If make it more efficient, what electronics should I go with - Trane XL80 or would something else be better/easier/less expensive.

It's a two burner unit, the house is 900sf built in 1924 and located in the Chicago area.

Thanks, pictures are below


Trane XL80 on the outside

No Trane XL80 controller board inside

Honeywell Hot Surface Ignition controller

Tranformers

Blower motor wiring

 

Trane, like most product manufacturers, don't manufacture all the components they use in their product. They purchase them from the component manufacturer. AOSmith (blower motor) and Honeywell (ignition module) are 2 examples. How did you conclude you sure you are missing a control board? The blower motor may have a problem starting because it's starting torque can't overcome a high resistance. When was the blower motor and blower last serviced? Have you tried operating the motor at a different speed? You always want the furnace to operate as efficient as possible because the source of heat is usually one of the most expensive items in a household budget. Why are you replacing the blower motor?

 

Trane XL80 is only a group.... not a model number. There could be many variations present.
Yes... the XL80 is listed as a four speed blower but it depends on what is selected.
Most don't use all fours speeds.
You could post the actual model number. It should be inside on the side wall near the burner.

I am not for making major modifications to a furnace. That is a gas fired UL inspected appliance.
Making major changes removes the UL listing.

 

Beelzebob: It was an assumption since the Honeywell Ignition controller is relatively new compared to everything else and others I looked at online have a controller board. The wiring diagram below says otherwise.

I am replacing the blower motor because when I pulled it out, it is well worn, sometimes will start right up and sometimes won't, the sound it makes when it does start up, and my electric bill keeps going up even though I am using the furnace less so far this year.

PJmax: The model number was on top of the unit - BLU070J936A0 manufactured 4/86


Wiring diagram

 

It's not missing a control board. I believe that furnace used a smart valve. All the controls would have be in the valve.The early smart valves were problems and intermittent. Looks like it was replaced with separate parts.

That is a four speed blower motor.
You can select two speeds..... heat and cooling. The other two are parked.

Be sure to have the heat exchanger checked on that 35+ year old furnace.

 

I went out and picked up a new run capacitor as the new motor was due to arrive.

Put the new capacitor on and tried it with the old motor - works fine now. Blower motor goes right on and stays on when in Auto until the temp is reached. Also seems to be reaching temp faster.

Perfectly happy not to have to replace the blower motor. It looks well worn, but as long as it works and isn't eating up as much power I'll leave it in and consider it $100 well spent to not have to. Much less than what my giant snow blower cost to stop it from snowing like it did when I first moved in - got well over a foot that Thanksgiving weekend in 2015. Six years and counting it hasn't happened again and only really needed it a couple times