Morning,

Moved into our house a few weeks ago. Our furnace hasn't worked properly since moving. In order to get it to heat we have to go down to the basement and turn the furnace off and back on.

The inducer runs constantly, from the moment the furnace starts up until the moment I flip the switch and turn it off. I've had the inducer run for an entire week before I caught onto what was going and at that point it was a nice 110 degrees from constantly being run. We had the limit switch replaced by an HVAC guy. A separate company ran the previous owners up on a $1800 bill and nothing changed in the symptoms.

I've been researching this furnace, the symptoms, and HVAC in general for the last three weeks and I believe that the problem is the board. The capacitor or the board for the inducer motor is stuck on. I tried tapping the capacitor but that didn't do anything. The furnace will heat when it's cycled off and on because the limit switch has a moment to tell the furnace that the motor isn't running, which I suspect is a requirement to turn on.

Once it turns on it will heat to what the therm says and then the flame turns off. The inducer remains on well after the heat has come down to an acceptable level. The inducer remains on until I physically turn the power to the furnace off, which has been as long as a week.

Anything I should try or anyway to test my hypothesis before dropping money on a new board?

 

I think you are probably correct, although the problem is more likely a stuck relay on the board rather than a bad capacitor. There is not much else that can cause this symptom.

If the thermostat was constantly calling for heat you might see this, but because the furnace turns off when setting is reached I think that can be eliminated. A failed limit switch would not cause the inducer to run continuously.

 

Relay, that's the word I was looking for! I rapped on all the relays with a screwdriver per a recommendation I read elsewhere to no avail.

The limit switch was replaced by a friend who is a plumber for the town. He doesn't have much knowledge of HVAC but I think he determined that the limit switch wasn't working, although he also called it a pressure switch, but I found the box it came in and it clearly says inducer limit switch-- maybe they're one and the same?

Anyways, I figure I'll replace the board. I don't really want to do it myself, but there are only two HVAC companies in town. One I have deemed as incompetent-- they billed the previous homeowners $1800 and didn't fix anything (or if they did it wasn't the problem we noted in the contract, since it's the one that still exists). They also installed my upstairs thermostat when they installed the upstairs HVAC system-- I found out last night that the upstairs heater hasn't been working because they never told the thermostat it was an electric heater and not a gas one and they wired the thermostat for a heat pump. The other HVAC guys would charge more for the service call than the board costs.

It seems that replacing the board is pretty low-danger job, am I right in assuming that? I won't mess with anything gas-wise, it took me a week to work up the courage to even open the furnace up.

 

If you can find an exact replacement board it is fairly straightforward. But sometimes only "universal" replacements or upgraded designs are available and they may be a little trickier. Manufacturers expect these will be replaced by a tech that can deal with small variations and need for configuration.

See what you can find for a replacement and post back here if you have any questions.

The general term limit switch is used for any type of sensor that verifies that some parameter is in the proper operating range. A go/no go type of "limit". A pressure switch is a type of limit switch that verifies that pressure or vacuum is within proper range.

 

A failed limit switch will usually cause the inducer to run and in many cases.... the main blower too.

XE90 is only a series. The model number is long and is on an ID plate inside on the side wall near the burner.

Without the model number I can't give you any exact advice but most furnaces have a control board with a diagnostic LED on it. There may be a little sight glass in the blower door where you can look in and see it flashing. The fault codes would be on the back of the blower door.

 

Thanks for the reply Pete!

We (Trane parts dealer and I) think we have found the model number for the furnace. The genius who put the furnace in also installed a drywall screw directly through the middle of both the model and serial number. We can be sure of all but two digits, but we think the model number is TUC060C936B6.

I took off the bottom door and found that the safety switch was taped so the furnace would stay on. Anyways, the LED blinks a slow, regular blink. This, according to the door, means everything is fine and there is no call for heat. When I turn the furnace off, set the thermostat to call for heat, and then turn the furnace back on I get a steady red LED which becomes a faster, but still regular blink. The door states this means everything is fine and there is a call for heat.

I'm currently trying to find a replacement board. The ones I have found do not look similar, so I am assuming they are for newer models or are universal. The control board in the furnace has three or four large black boxes across the top, and the replacements are all missing these which causes me some concern. The Trane suppliers won't talk to me because I don't have a license-- though he was kind enough to assist me in finding the number.

 

This is in response to an earlier post regarding an inducer motor that kept turning on and off during the fan run out cycle. I have a Frigidaire furnace that has experienced many different problems over the 15 years it has been in operation. The newest problem that arose was that the inducer motor would kick itself on after it had turned off for fan run out cycle. This would happen randomly for about 30 to 60 seconds and then it would calm itself down. This problem started after I installed a new Honeywell Thermostat. My old stat did not require a C wire for 24VAC. After adding this to furnace and to the stat is where the trouble began. I tried to terminate the wires again to clean up some sloppy wiring but this did not help and there was no wire wiggling that would cause it to happen either. The only new element in the mix was the C wire to the new stat which also connected to the AC unit outside. As a last resort I decided to pull the fuse out of the AC power box outside to remove any possible voltage leeks that could have been coming from the AC unit and the problem disappeared. After much trouble shooting with this unit it is finally running as it should.

 

Take a look at my post "rhynes57" there may or may not be any correlation but it is worth a try. If you do not have a power box outside to remove the fuse link you can turn off the breaker inside the house for the AC unit. The other strange thing that would happen was the blower motor would turn itself on for the 120sec run out randomly as well. These problems all went away when I removed power to the AC unit. Either way I would always recommend removing power from you AC unit to avoid any accidental startups which will destroy the compressor in the cold weather.

 

Welcome to the forums.

Many stats require a C connection and it should not cause a problem like you're having.
You should not need to turn the A/C condensor power off.

 

Hi Ian,

I came across this post as I am now having the exact sam issue as yours with my Trane XE90 furnace. Was wondering if you ever ended up replacing the control board and if that help solved the problem for you. Thanks.

 

Are you getting a trouble code on the control board?

 

Thanks for your response.

Most of the time the operation is normal except for the fact that inducer never stops running (even when t-stat is set on low or completely off).

Every once in a while the blower stops working and I get the 3 flashes on the LED (pressure switch?) but the inducer is still running. To fix that I turn off the power to the furnace for about 15 minutes and turn it back on, furnace starts to run normal again for a while but the inducer never stops working (even when desired temperature is reached).

I doubt it is the pressure switch based on all the research that I have done. I think the 3 flashes is just a ripple effect from the fact that inducer never stops... but hey what do I know

For what it's worth I have cleaned out all the drain pipes, exhaust pipe and fresh intake. There don't seem to be any blockage.

 

If the draft inducer is running before a call for heat...... when the call for heat is made the board should display a "pressure switch closed before call for heat" code. You should not get a flame if the inducer is previously running.

This problem would point to a problem control board.

 

Thanks, Pete. Yes sometimes the behavior is exactly as you described. I will call around and see if I can find and replace the board.