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Discussion Starter · #1 ·
Our furnace is a Trane XL80 TDD080R936E0 and three days ago we woke to a cold house. The control board was 2 red flashes/pause/2 red flashes/pause, which according to the Service Facts sheet means System Lockout (Retries or Recycles exceeded).

The house was originally heat only, and AC was added several years later. It is a downflow furnace that sits on top of the evaporator coil. There are no filters in the furnace, the system relies on filters in the return vents. I have been maintaining the appliances for years, same with the cars, but with two high risk people in the house, am facing my first effort on the furnace. Last time the problem was clearly beyond me, and the igniter and control board were replaced in 2011.

When power is on there is a quiet background hum coming from the furnace.

To force the blower to operate, the thermostat setting was changed from Auto to Fan, the panels removed and the 'open panel' trigger locked closed:

A) When the thermostat does not call for heat, the control panel blinks green

B) When the thermostat calls for heat the control panel blinks yellow, the furnace ignites, the inducer fan starts, but there is no blower action.

C) To verify the blower not functioning, changed thermostat to AC and forced the AC unit to click on, and refrigerant could be heard circulating through the evaporator coil. No blower.

It seems obvious that the blower has died.

However, it would be crushing to go to all the effort involved and discover that it was not necessary because my analysis is wrong.

Are there any switch/interlock conditions that I can check which could cause the same symptoms?

If it is necessary to fix the blower, my biggest difficulty is accessing the blower compartment.

Being a downflow, the exhaust pipe runs through the center of the furnace down to the combustion chamber, so before the control board and the sheet metal cover over the blower compartment can be removed, the exhaust pipe has to come out.

The exhaust pipe joins the roof exhaust just below the ceiling but there is no flex movement that I can see. The exhaust pipe is screwed to the flange on the inducer and that has no flex. The roof exhaust pipe is fixed, so it looks as if the inducer has to be removed, so the flange fan be removed, so the exhaust pipe can be separated to drop through the combustion chamber.

A picture is worth 1,000 words, and there are photos at tinyurl.com/y97t5vft

I am hoping someone with experience in downflow blowers may know of an easier and simpler way to proceed.

My thanks in advance.
 

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"B) When the thermostat calls for heat the control panel blinks yellow, the furnace ignites, the inducer fan starts, but there is no blower action"

When you say "ignites" do you mean the gas valve opens and the burners light up? This shouldn't be happening before the inducer fan starts up. Or do you mean the hot surface/piezo igniter operates (I'd still be surprized if this happens before the inducer runs but I guess it's possible).

In any event, if you suck on the tube from the inducer to the pressure switch, do you hear a click?
 

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Discussion Starter · #3 ·
"When you say "ignites" do you mean the gas valve opens and the burners light up? This shouldn't be happening before the inducer fan starts up. Or do you mean the hot surface/piezo igniter operates (I'd still be surprized if this happens before the inducer runs but I guess it's possible)."

I did not mean to imply an order to the events. By the time I moved from raising the thermostat to the furnace the light was yellow, the exhaust fan was running, and the furnace was igniting.

"In any event, if you suck on the tube from the inducer to the pressure switch, do you hear a click?"

There is no tube, so this unit may be pre-inducer (there is a photo at tinyurl.com/y97t5vft)
 

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That unit has an inducer.

You'll have to see if the control board is applying power to the blower motor - the board is accessible without removing the exhaust pipe.

Do you have a multi-meter?

One thing to not is that it looks old, dirty and not maintained so it may be wise to call a pro in for complete service/cleaning. When furnaces hit 15+ years old they need more attention -> ie checking to see if there's a safety issue.
 

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Discussion Starter · #5 ·
The unit is early 200x, repaired in 2011 and last serviced in 2017. As for dirty, the calcium around the exhaust joint, below the igniter and on the floor is the product of rainwater in the pipe before the roof was repaired. The dust comes from the whole house fan which exhausts air into the attic and the cabinet is open at the ceiling, you can see the vent to the right of where the exhaust pipe enters the ceiling.

Under ordinary circumstances I would be calling the installer but these are not ordinary times. There are two people rated at highest risk in the house so we are in total isolation, and likely to be that way for the foreseeable future.

The control board is a 1049P 7/2010 build, 50M51-495-90 / D344301P01 / CNT06424 but I have no wish to start probing without reading a manual first. It seems there are no Trane Service Manuals anywhere on the internet, and am reluctant to go in blind. At upper left are what I assume to be the Y/B/R/B motor wires because of the AWG but have not tried to test them because the only time the fan would be on, the furnace is operating.

Capable, but nowhere near competent without access to a Service Manual.
 

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This unit has a regular psc fan motor so troubleshooting is pretty straight forward.

If the blower is not coming on in heating mode, the burners should stay on in heating mode until the high limit switch opens. Does that happen?

You need to use a meter and check between the blower neutral terminal and low heating terminal.

If you have a 2-stage thermostat, disconnect the wire connected to W2 and tape it off so it stays on low fire while doing testing because it may go on to high right away or after a short delay.

30 to 60 seconds after the burners light off, the board should apply power.

If power gets applied, you need to recheck the blower terminals see if they're tight/making contact.

If the board is okay and power is being applied, you'll have to remove the exhaust pipe, the access plate and check the motor's capacitor - also give the wheel a spin and see if it moves with little to no resistance.
 

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Discussion Starter · #7 ·
"If the blower is not coming on in heating mode, the burners should stay on in heating mode until the high limit switch opens. Does that happen?"

That is my assumption, as the control board's flashing sequence when I opened the cover was that of System Lockout (Retries or Recycles exceeded). Those codes stopped after I started the troubleshooting.

"You need to use a meter and check between the blower neutral terminal and low heating terminal."

The Y/Blue/R/Black wires are noted on the control board as Park/Heat/Heat/Cool and have staggered terminals. The thermostat was set to Fan to make sure the blower would be called for and as Blue Heat was the top terminal it was easiest to check. It had 118V, so you have helped me confirm the blower is at fault.

"you'll have to remove the exhaust pipe,"

That is the biggest problem I face.

Removing the exhaust pipe is non-trivial, and the method I outlined is clumsy. That's why I am hopeful someone experienced in bottom flow furnaces has been there, done that, and knows a smarter way to remove the exhaust.

BTW, when I eventually get to the blower chamber and it is not the capacitor, is there any alternative but a hub puller to separate the motor and squirrel fan? My workshop is well equipped and has a hub puller for brake drums and the like, but it is not suitable for a fan.


Thanks
 

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There's a set screw that gets loosened and the motor lifts right out (after mount is unscrewed too) - if you're lucky.

You can try sanding the shaft and using a penetrating oil, there's always a risk of needing a hub puller.

As for the exhaust, I have never worked on a down flow furnace but it looks like it comes out with a few screws. Hopefully someone who has will see this thread.

You may need to disconnect the exhaust outside of the furnace before being able to remove the internal section.
 

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Discussion Starter · #9 ·
"As for the exhaust, I have never worked on a down flow furnace but it looks like it comes out with a few screws."

The screws are not the problem, the top pipe has to be lifted up to free the lower pipe or the lower pipe has to be pulled down to be free of the upper pipe. There is no space to do that. It is the same problem plumbers faced on drainage pipes before Fernco sleeves came along.

"You may need to disconnect the exhaust outside of the furnace before being able to remove the internal section."

There is no pipe movement outside the furnace, the exhaust exits through the roof and is locked in place up there.

The pipe is in two sections before it reaches the twisty which aligns the roof exiting pipe with furnace pipe. The 3' length can be released by removing the inducer to release the flange. I will have to jury rig something underneath to prevent the pipe being lowered more than a few inches because it would hit the igniter if I accidentally let it drop into the combustion cabinet.

Above the 3' extension is a 9" which connects to the twisty and that will have to be removed too because the opening for the exhaust in the top of the furnace is less than 1" wider than the 4" pipe and I need to tilt the 3' section sideways to remove it.

My searches on youtube have turned up nothing about removing an exhaust pipe running through the blower cabinet, so either there is a paucity of downflow furnaces or nobody sees it as big a deal as I do. It is not a complex task and if there is no way to remove the exhaust without removing the inducer, that's what I will have to do.

Thanks
 

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the inducer may have a gasket behind it which can get damaged when removing it.

loop up the inducer part and see if a new one has replacement gasket.

usually you can find the manufacturer's inducer replacement instructions.

it may need high temp rtv silicone applied or gasket changed when inducer is removed then put back in.
 

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Discussion Starter · #11 ·
"the inducer may have a gasket behind it which can get damaged when removing it."

Which is why I am so reluctant to remove it.

"look up the inducer part and see if a new one has replacement gasket."

Have spent most of the day hunting for part numbers, and tracked down GKT03081 Furnace Inducer Draft Blower Gasket on ebay so am feeling good, it will be here next week.

"usually you can find the manufacturer's inducer replacement instructions."

Trane information is thin on the ground. Have been able to use other sources so far, but would be far more comfortable having a Trane Parts Manual with exploded view drawings. www.partstown.com has manuals for hundreds of manufacturers, but not Trane. www.heritageparts.com has en empty list of 'View Manuals'.


The capacitor is a possible cause and a motor is $200 so will start the repair with a new capacitor, and if it doesn't fix things will wait the extra days it takes to get a motor delivered. Fortunately it is not the middle of winter.

When the blower is functioning again, the capacitor will be relocated to the outside of the blower panel so that if this ever happens again it will be easy to replace.
 

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Discussion Starter · #13 ·
I've already confirmed there is power on the controller board when the burner is running.

If there is more diagnosis to be done, then what are the other tests I can do?



The last thing I want to do on this furnace is pull the exhaust system apart to get at the blower.
 

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considering the blower didn't work in a/c motor either, it's most likely not an individual speed tap but a bad capacitor, electrical failure which affects all speeds or bearing failure.
 

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Discussion Starter · #16 ·
Progress report:

The disassembly of the exhaust was straightforward, removed the screws holding the exhaust pipe sections together, removed the exhaust screws pipe to the inducer's flange, and unscrewed the inducer. I was able to separate the exhaust sections and remove them from the cabinet.

The motor leads were pulled off the control board, and the neutral wire separated from the bundle. This let me move the harness away, and revealed that the multi-connector on the control board was melted on one side. Closer examination showed nothing to indicate that this was an internal short. I cleaned off enough of the melted material to see inside and all three connectors were bright metal and the insulation showed no sign of melting. It looks as if an external heat source melted the connector and the material flowed on to the wires. You can see how it look at tinyurl.com/ybzntwdv

With the wire bundle connector unable to be separated from the control board I had to remove the blower panel with everything in situ, and set the panel to the side. This gave me access to the chamber, so removed the capacitor and tested it as per tinyurl.com/yygzzbxp - the original GE 97F5705 did not react at 200k, the replacement did. Out with the old, in with the new.

Tomorrow I will build a pair of 14AWG extenders so that I can mount the capacitor on the blower panel. None of the cable insulation looks to be high temp, so will use 14AWG Rolex.

The gasket material around the blower panel has dried out, it looks like dessicated foam weatherstripping for windows. There are no Trane part numbers for sealing around the blower panel, so am guessing that is what was used originally.

When the blower panel is back in place I will test it by using the AC. If it does, re-assembly will have to wait until the inducer gasket is delivered.
 

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Discussion Starter · #17 ·
Completion

The capacitor did not need extenders, the leads were long enough to reach outside the blower chamber and the capacitor fitted neatly under the control board (as can be seen at tinyurl.com/ydyyu5bw). The capacitor was a sloppy fit because it had originally been mounted on the curved drum and was not against a flat surface, but mounting a short strip of 3/4" hook underneath it firmed things up.

After setting the thermostat to fan and turning on power the blower sprang to life. If the new capacitor fails it will be a simple swap, not a major effort to replace it.

Re-installing the exhaust was a pain. The exhaust pipe had to be re-assembled and raised into the roof pipe, then held in place by cord.

The original inducer gasket was filmy fiberglass which disintegrated as the inducer was being removed. How to keep it in position while positioning the inducer into the exhaust was a concern until the replacement gasket arrived. It is a formed material which was easy to hold in position with twist ties in two of the screw holes.

The inducer was inserted into the exhaust flange and a pair of screws were used to hold it loosely in position. The twist ties were removed and all the screws fitted and tightened down. Next the flange and exhaust were screwed together.

Plugged the inserter connector into the harness, put the covers back, and turned power on. Set the thermostat to heat and everything was back to normal.

What would have been a couple of hours at most on an upflow took way longer because of having to remove and replace the exhaust before being able to get into the blower chamber. The most expensive part was the Inducer gasket.
 
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