Trane XE 90 pressure switch

Remove the hose from the low pressure switch and plug. The control board will then run the inductor fan at high speed which should cause the high switch to close and allow the ignition phase to begin. This should allow the furnace to run on high only till you can get a new low switch.

I have a similar problem. I have ruled out pressure switch which I have replaced. Exhaust seems unrestricted outside the house. There is not enough vacuum for the pressure switch to be activated. Could this be a heat exchanger problem?

Hello everyone I'm new to the forum but see this site is very informative. Right now m having he 3 blinking lights error on my Trane XE90. I removed the inducer blower and it spun free no blockage. I also checked outside in the pipes and they looked good also. Now I removed the little rubber hoses starting with the one on front of the pressure switch and the switch spilled out a good amount of water. I take it that's my problem? I let it drain and took off the pressure switch and drained all the remaining water out of it. I'll hook everything back up and see if it work now? What could be the cost of that switch filling with water? I'm putting two and two together and thinking something has to be clogged. What should I check?

Thanks
Nate

NATEHAWK said:

Hello everyone I'm new to the forum but see this site is very informative. Right now m having he 3 blinking lights error on my Trane XE90. I removed the inducer blower and it spun free no blockage. I also checked outside in the pipes and they looked good also. Now I removed the little rubber hoses starting with the one on front of the pressure switch and the switch spilled out a good amount of water. I take it that's my problem? I let it drain and took off the pressure switch and drained all the remaining water out of it. I'll hook everything back up and see if it work now? What could be the cost of that switch filling with water? I'm putting two and two together and thinking something has to be clogged. What should I check?

Thanks
Nate

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The switch needs replaced if it was water logged. Check the drain trap. Remove it and run water through till all the debris inside is gone. Also, make sure the drain hoses from the inducer and cold header to the trap are free and clear of debris. This is what would have allowed water to reach the press. switch.

Hi everyone, I've been dealing with the same problem for a couple years, but it's getting worse. In the past, the unit would cycle a couple times before igniting and providing heat. Toward the end of last spring I awoke to a few cold mornings and found that if I pulled the small hose off the front of the pressure switch, I'd hear the 3-clicks and it would start working. Now it's getting cold again and doing the same thing, so I ordered a new pressure switch. Same problem!

So, it appears that the front side of the pressure switch isn't getting enough pressure. What I've noticed with the new pressure switch is that if the draft blower starts, and I'm getting the 3 blinks on the LED panel, I can pull the front pressure switch hose and blow air toward the hole and it will start. I'm not even touching it, just blowing air at it. This tells me that the pressure on the back-side of the switch is VERY close to being enough to close the switch. What could cause the pressure to to be like this? I've checked all the vent lines, in and out and they appear very clean. I don't have a sag in the line, so I'm stumped. Any help is greatly appreciated!

Also, how do you know if the 1.40" WC switch is right for my unit?

Remove and clean the drain trap.

Thanks for that, HVACTech. I was looking at that thing today, but I didn't see how it could have any effect on the pressure switch. Can you elaborate a bit?

Update: It took me about 15 minutes to remove, clean and reinstall the trap, then test. It didn't fix it...still getting the 3 flashes.

lostpilot28 said:

Thanks for that, HVACTech. I was looking at that thing today, but I didn't see how it could have any effect on the pressure switch. Can you elaborate a bit?

Update: It took me about 15 minutes to remove, clean and reinstall the trap, then test. It didn't fix it...still getting the 3 flashes.

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Also, would a weak draft inducer motor cause this? My heater is 8 years old and I would think they'd last longer than this. Is there a way to test or check the motor or impeller (whatever it is) to see if it's good?

the proper way to find out whats going on with the unit is through the use of a dual port manometer or a magnehelic. These are specialized tools. You may want to call a pro. But before you do.... Do you hear water sloshing around in the inducer while it is running? Follow the pressure hoses back from the switch where it enters the cold end header of the heat exchanger (to the left of the inducer... should be a clearish hose) make sure that port is free and clear of any debris.... use a piece of wire or a long drill bit and put it through the port to ensure it is clear. Much beyone that and you will need a pro or some specialized tools.

Thanks again...I've cleaned the hoses to the pressure switch, and I've verified they're not blocked on the header. There is no water sloshing around in the inducer. Any further ideas?

blocked intake or exhaust..... if you remove the burner box door and then fire the furnace does it run? if so ensure the screen where the intake pipe enters the box is free and clear of any debris and ensure the intake is clear of debris as well....(the hole piping system, not just as far as you can look into the piping.

Alright...here's an update. I decided to call my heating repair guy. I wasn't home, but the wife was...he apparently looked inside with a borescope camera and told my wife there was a crack in the heat exchanger and showed her a picture of the inside of my furnace. She said it looked rusty, which I'd expect to be somewhat normal.

So, he tells my wife it's a replacement heat exchanger (possibly around $400) or an entirely new furnace (possibly around $1,600). What do you guys think? Ever heard of a cracked heat exchanger causing this problem? If so, is it fixable? Welding, etc. I didn't know that gas furnaces had heat exchangers.

depending on the vintage of the Trane XE90 furnace you have, it is possible that it is cracked, but on anything within the last 15 years SHOULD be a serpentine style heat exchanger. I have only seen a trane serpentine style heat exchanger cracked 3 times, so it's unlikely but still possible. On all heat exchanger failures you should get a second opinion and be home for it! Most HVAC companies will do these at no charge as it is usually a lead in to a sales call, but I am leary. can you take a picture of your furnace and post it? Just so I know the vintage of yours.... or you can post a model and serial number. Trane usually had a 20yr part warranty on the heat exchanger which provide you the part and you would be responsible for the labor to put it in. $400 sounds very cheap for the labor. The American Gas Association ( the authority on furnaces and heat exchangers in America) gives you 2 options ... 1. replace the heat exchanger 2. replace the furnace. The price of $1600 sounds outrageously cheap! Cheap usually means poor installation and less life expectancy from the equipment.

Well, I wasn't there to hear everything that he said...so I may need to talk to him on the phone today. I think a 2nd opinion is in order. I am the 2nd owner of the home, so I think the heat exchanger has a 20 year warranty. He said I'd have to pay $100 for shipping and around $300 for labor to install the new one. Is $400 for this service expensive? I've read elsewhere that it takes between 2 and 6 hours to replace a heat exchanger. Not sure what this guy's hourly rate is, but $400 seems high.

The model number of my XE-90 is TDX100c948c2.

lostpilot28 said:

Well, I wasn't there to hear everything that he said...so I may need to talk to him on the phone today. I think a 2nd opinion is in order. I am the 2nd owner of the home, so I think the heat exchanger has a 20 year warranty. He said I'd have to pay $100 for shipping and around $300 for labor to install the new one. Is $400 for this service expensive? I've read elsewhere that it takes between 2 and 6 hours to replace a heat exchanger. Not sure what this guy's hourly rate is, but $400 seems high.

The model number of my XE-90 is TDX100c948c2.

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Does this price include schooling, overhead, insurance, plus the mans wages?
Paul

lostpilot28 said:

Well, I wasn't there to hear everything that he said...so I may need to talk to him on the phone today. I think a 2nd opinion is in order. I am the 2nd owner of the home, so I think the heat exchanger has a 20 year warranty. He said I'd have to pay $100 for shipping and around $300 for labor to install the new one. Is $400 for this service expensive? I've read elsewhere that it takes between 2 and 6 hours to replace a heat exchanger. Not sure what this guy's hourly rate is, but $400 seems high.

The model number of my XE-90 is TDX100c948c2.

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that price is very cheap in my area.

I read this thread and I thought I had a similar problem. I get the three blinking lights every day and need to manually reset the furnace.
I replaced my pressure switch and I still have the problem.
If I shut the furnace off and turn it on, the furnace will light.
If I squeeze the tube to the switch and release, it will light.
If I take the tube off at the switch and put it back on, it will light. If I even hold it close enough to get some vacuum to the switch it will close and light.
The furnace is very new and there is no sign of any dirt or moisture anywhere.
I replaced the switch because it seemed to me that perhaps it was sticking and needed to be opened and then closed again in order for the contact to be made. Replacing the switch proves it is not the switch. There is plenty of vacuum to close the switch, so it is nothing between the switch and the inducer.
What else could it be?

I've been struggling with the same problem for years. 3 blinking lights, reset the furnace, replaced the pressure switch, checked for leaks, water, air, everything. Just had a repair guy in today. Everything checks out. Good man. As we were winding things down, he mentioned that a strong gust of wind, in just the right direction, could trip the pressure switch and shut down the furnace. There was no hesitation on my part in answering him. "Every time this has happened, there has been a strong wind." He said, instead of removing and replacing the hose from the front of the pressure switch, all I had to do was reset the furnace, meaning, just turn it off and on at the switch. So folks, it's not your pressure switch, it's not water, it's not your heat exchanger, no, it's not the logic board. It's simply one thing, WIND!

Then I say that is a bad design. Wind was my first thought as the first time it happened, it was indeed very windy. Since where I am from, the wind is almost always from the west. I could see that perhaps wind from an unusual direction could cause this and that is why no problem for the past 4 weeks.
I guess this means we will never be able to go on vacation again!

Well, no. Sorry, I don't believe that for a second...unless you put your furnace outside, or very near an opening. My furnace is as far inside my garage as it can go. Not affected by wind at all.

But, as a follow up to this thread, I'm STILL trying to get this issue resolved. My furnace has worked (albeit stubbornly) for the past 3 months (with my occasional intervention). But I'm sick of it, and so I had the repair guy out again. We tested several things and are convinced it's the heat exchanger that's cracked. Using his digital manometer, we found that the pressure differential between the front and the back is only about 1 in/H2o. It should be much higher, since the pressure switch is rated at 1.4 in/h2o.

Also, and this was interesting, water was building up inside the draft motor fan. The water tubes were clear, but when we put the pressure gauge on the water trap (where the draft motor drain plugs in) it read about .5 in/h2o positive! Basically, that pressure was preventing the water from draining out of the draft inducer. He believes the pressure should've been zero in the water trap, but since it was reading positive pressure, that was most likely from a crack in the heat exchanger.

So, he's ordering one under warranty. I'll let you guys know what happens.

BTW, a run down of what has been done so far: replaced the pressure switch and tested the old one (it was good). Checked the draft inducer inlet and exhaust - both clear. Aside from those things, what else could cause a "too low" pressure differential? The draft inducer motor is one and the heat exchanger is the other. The draft inducer seems to run great, although we couldn't verify if it was running slow. I don't think it's the draft inducer motor, though.