Trane XL95 HE Gas Furnace Inducer/Pressure Switch Error

Old 11-01-18, 05:58 PM
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Trane XL95 HE Gas Furnace Inducer/Pressure Switch Error

Hey Everyone,

My furnace has been on the blink for a while now, looked at by a general repairman friend a number of times, and now it has gotten to the point that I either need to get it fixed or get a real professional to come in and get it done right. I've been hunting around the internet for answers, and really just at the end of my rope here.

First, the problem: While everything is connected, furnace starts up, pressure switch (I believe) clicks closed but the heating element does not turn on. There's a motor engaging, but after 5 speed-ups, the system disengages with the 3-flash error code for the Inducer Fan or Pressure Switch. This error code remains flashing through the next cycle until the moment that the furnace should activate, then disengages and errors out again.

Checks so far:
1. The pressure switch has been replaced with a new unit, and is not faulty. It is noticeable that it closes when pressurized (more on testing oddities later).
2. Vent pipe is clear. There was a bird nest in the vent pipe, that has been removed, the pipe cleared, and an elbow with vented cap placed at the end to prevent further birds and/or critters.
3. Condensate trap was checked, and was half full of water. That has been cleaned out and placed back in the system.
4. Pressure tube has been checked for cracks/leaks off the system. Tubing appears good. Tubing connected to the pressure switch appears good, no condensation. No noticeable sounds of condensation inside the pressure switch.
5. The pressure tube running between the pilot chamber, gas control valve, and pressure switch is square rubber tubes (3) intersecting at a T-joint, two longer tubes running to the pilot chamber and pressure switch in direct line, and a shorter tube connected off the T-joint to the gas control valve, ended at a plastic L-joint that goes into the gas control valve. The end going into the GCV is slightly looser fitting.

Current testing: Today, I have been trying to diagnose the problem further. I have been checking the system through trial-and-error mostly. I've been manually holding the safety latch while manipulating the pressure tube to test how the system responds to variances of pressure.

First test, I've noticed that while everything is properly connected, as the system begins to cycle on, the heating element inside the pilot chamber does not engage. The system eventually turns off and errors out.

Second test, while starting the system again with the pressure tube removed from the GCV (but still engaged with the pilot chamber and pressure switch), the system cycles up halfway through the start-up. The heating element engages, but the system does not proceed further into the start-up cycle.

Third test, while repeating the second test, at the point the heating element engages, the pressure tube was replaced into the GCV (everything now connected as normal). The system began to proceed further through the start-up cycle with the heating element still engaged, but reached the same point as the first test, shut down and errored out once again.

Fourth test, repeating the third test up until the system was just about to shut down and error out. At that moment, removed the pressure tube from the GCV again. The furnace engaged fully, gas was fed into the chamber and ignited lit it normally would. But the furnace was not fully engaged (I don't believe). Replacing the pressure tube into the GCV once again caused the furnace to shut down and error out.

I think there may be a problem with the tubing itself, either with the connector pieces or with the connector going into the GCV (possibly that it is not keeping a good seal). What do you guys think? I mean, if any of the parts weren't working properly, the system would reach the point of firing up, even though it took some serious timing and manipulation, right?

Old 11-01-18, 11:07 PM
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Welcome to the forums.

Almost impossible to follow your diagnostic tests there.

A pro uses a manometer to actually check the vacuum that is generated from the draft inducer. You are only guessing. That makes the repair difficult. The pressure switch must be open before any call for heat. It must then closes within a few seconds after the draft inducer is started.

I usually connect my voltmeter to the two pressure switch leads to monitor operation. Before a call for heat.... there will be 24vAC across the switch. After the inducer starts..... that should become 0v.

A typical problem with draft inducers is that the orifice where the hose connects to it is plugged..... usually with rust. The hose connects to a 3/16" ferrule. The orifice is down inside that fitting. It is very tiny and must be cleaned. Small piece of wire, pin or wire brush bristle will work.

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If you read other threads posted in this forums...... you'll see more than half of them are the same exact problem that you have.

Old 11-02-18, 04:20 AM
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It was actually more simple than that. I here looking at the internal components while missing the very obvious lid my live-in decided to use to cover a circular vent on top of the furnace at some point.

I missed it. Heating/cooling friend missed it. Everyone missed that, despite being different sizes, she goes "Huh. Round. Round. This must go here!"

Sorry... but thanks for the response. Lesson learned... take nothing for granted, check the simplest, dumbest stuff imaginable first, because you never know who is going to do something incredibly dumb.
Old 11-02-18, 04:44 AM
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A lid covering what? The air intake?

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