glennjanie

Ah-Ha, a 2-1/2" sag in the flue line. That is a plumging problem on a "condensing" furnace; with that much sag the water had him cut completely off.
Glenn

scott

I awoke this morning to a FREEZING house...my furnace had stopped working. The blower kept cycling on for about 30 seconds then off for about a minute. I investigated to discover the diagnostic light flashed 3 times when the furnace was supposed to be on. A search for "trane xe90 pressure switch" brought me to this thread.

After reading Aceinstaller's checklist that it might be related to my flue (which I doubted), I thought I'd check anyway. Sure enough, a wasps nest had been created sometime over the summer just inside the 3" PVC pipe on the outside of my house...large enough to block 80-90% of the exhaust air. How it affected the "pressure switch", I don't know...BUT, removing it solved the problem and my furnace is working again.

Just want to thank everyone here for not only saving me the expense of a service call but the discomfort my family would have experienced while waiting for it (temps hovering around 0C/32F last night).

...off to purchase some wire mesh!

Cheers.

Ponte

I also have a Trane XE90 and I've been dealing with this problem for the last month. I think it is time to replace the pressure switch. How does one go about doing that? Is it a DIY fix or does it require bringing someone in?

novice

I have a Trane XE 90 furnace which is in the second heating season. I've just recently had the same problem with getting the code flashing 3 times. After having someone not associated with a Trane dealer troubleshoot my furnace, and finding no problem with any of the usual switches or diaphragms, we were at a loss, thinking the problem must be in the circuit board when we discovered the problem. The problem was with a connecter at the upper left hand side of the circuit board not being completley snapped in place on the left side. It had been arching and had finally got to the place where it wasn't able to make contact any longer. It looked as though it had never been completly seated from the factory. It seats on both sides and is fairly robust in it's seating as it took a little effort to get it to snap in completely. After cleaning the contact of both the male and female at the far left side of tne connecter and putting everything back together, I've no other problems and the furnace is working fine. I don't know if this will help anyone, but just thought that I would let everyone know of this possibility.

lputnam

Had the same exact problem. Three flashes on the LED (pressure switch problem) . Pulled off the tube on the furnace (not the pressure switch) and there was a clean white spider web completely blocking the hole. I pulled that out with a paperclip and behind it was a dead spider. Could not see this until removing the tube. All is 100% working again. Thanks for saving me about $250 in a service call and the replacement of a pressure switch that was indeed working just fine.

MrMiz

Ok I know this was posted in 2006 and it's 2009 now but I wanted to toss my 2 cents out cuz this saved me more than $100... oh and bob villa sucks! Bob if your reading this you need to hire ME as your DIY guy. Why because I have absolutely no qualifications and I fixed this myself! Even though your web site thought I needed to spend a lot of money. I can hardly spell yet I fix problems like this. You do not want to get me started on how much I hate Professionals thinking they are the only ones in the world that are capable of working on anything.

Anyway lets break it down.... I had flying ants this last summer. They get into everything. Down exausht vents into tubes that lead to fancy pressure sensing devices. I vacummed up what I could. I pulled off the tube to the sensore and crunched up and cleaned out the dead flying ants. Used a paper clip in the small sensor part as recommend by this web site.. I think I looked at a lot of sites and bingo no more 3 flashing light errors. Furnace kicks on and MrMiz's buns are toasty!

My after thoughts. LEARN basic SAFETY measures and you can do and tinker with anything! Oh yah and this site rocks and you genious out there that give me the info. You rock even harder.... my socks have been rocked.

glennjanie

Welcome MrMiz:
We are happy it worked out for you; now you can give advice to anyone with 3 blinks!
BTW, It takes a very narrow minded person to spell a word only one way.
Glenn

manofsteel084

All the information is great. Problem is, I have no idea what hoses to pull off and check. Can't find a diagram anywhere. I am getting the three blinking lights and the small box on the black fan is heating up so I shut everything off. Any help with diagrams or "how to".... is GREATLY appreciated.

Jimm Two

All this information was very very helpful. I also had this 3 flashing code; I followed the steps recomended here.
What i found was on the exhaust out side there was a course screen to prevent birds from getting in, but on the intake there was nothing .
Found at the entrance to the furnace ( on the intake side) a wasp nest plugging off the air from comming in. I cleared the intake completely and put a small screen mesh over the opening to allow lots of air but with little or no restriction. Pushed the run program and the furnace was working.
Thank you guys for all the help this was great. Jimm

Bubba123

Just signed up to the forum to thank everyone for saving me a bunch of money!

On a Trane gas furnace TUE unit we got the same three flashes which indicates the pressure switch. A/C guy brought out a new unit and still no dice. We checked all hoses/exhausts and everything looks good. Read this thread at the same time he is doing all of this.

At this point he is convinced I need a new board.

Can we just try to re-seat all connections etc.?

"Sure, he says - might as well try".

Wouldn't you know... unit comes right on. We put the old switch back in and e-voila, everything is still working!

A/C guy didn't even charge me for the trip or anything. (I still tipped him.)

THANKS ALL!!!!!!