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Trane XR90 - 3 Red Lights

111K views 73 replies 10 participants last post by  dr3 
#1 ·
Hi
I was hoping someone could help me. I have a 6 year old Trane XR90 Furnace that blinks 3 red lights when it calls for heat, then it shuts down.
3 Red Lights means “Pressure Switch Error”.



This is what I have tried to fix this.


· I have unhooked the hose that runs from the switch to the gas valve and to the burner box and cleaned the hose. I have also cleaned the barb the sticks out of the burner box.
· I have checked all the clear drain hoses in the furnace to make sure they are attached and not pooling water.
· I have checked my outside vent – it is not blocked and it exhausts when the furnace runs.
· I have installed a new furnace filter.


Here is some history. This has happened in the past (last year and the year before if I rember right) abd cleaning the barb helped, cause after I cleaned the barb form the burner box when I hooked the hoses back up the furnace worked.


This is not the original pressure switch. When it was under warranty I put a service call in and the first tech that came changed the switch out. But the next tech that came the day later because that didn’t fix the problem found the problem to be the outside vent was iced over. Not sure it this means anything or not just wanted to add it.


Now the weird part, right now the furnace works fine (cycles fine) when the hose that runs from the switch to the burner box is unplugged. But soon as I plug it in it will call for heat and shut down and blink 3 times.


Can anyone help me? Any ideas what is going on?
 
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#70 ·
For anyone who cares, here is an update on this.

Today, the job was finally completed.

A couple of weeks ago they guy came with just the transition piece (plastic part between the inducer and the 2nd heat exchanger). The screws from the factory cracked it. But it was really obvious more was need as once he took off the inducer we could see lots of rust and corrosion and a crack from the dripping corrosion on the front plate of the 2nd heat exchanger. So we still had a code 3 after the part was installed.

So today he came back with the entire heat exchanger and installed it and so far everything seems to be running fine.

I just wanted to thank everyone who posted advice and especially thank HarleyRider. Your advice was spot on and invaluable, it really helped me a lot on dealing with this.

Cheers!
 
#72 ·
Thanks for the tips guys. I was able to save myself a huge repair bill by following your collective advice. I checked and cleaned the P-Trap, checked my pressure switch, all seemed ok. My furnace is mounted horizontally in the attic crawl space and vented almost directly above through the roof. SO take the tubing off at the burner plenum and the furnace starts and runs. Take the cover off the burner plenum and find several small wasp bodies! check the air inlet screen, and viola, found their nest sucked in. Cleaned everything up and reassembled, furnace started properly!
 
#74 ·
Morning all - Good news I had the 3 blinking lights and did the steps below to clear the issue.
Clean the input pipe screen at the center of the unit where the PVC input pipe is. Lots of bug shells and junk clogging the input.
Take off the burner cover and vacuum the inside nice. this is on the other isde of the input pipe and you take four screws off
Run some hot water into the output vent pipe to clear and ensure the drain pipes are good.
Clean and remove the water pipe collector piece and wash out the gunga inside.

seems like this is good maintenance and it only took an hour or so. Good luck out there
 
#2 ·
You're saying with the hose completey off thus removing the pressure switch's ability to close (which is the proper sequence of operation) which allows a furnace to run, it's running?

You can also clean the barb on the pressure switch. SPIN FAN SLOWLY WHILE CLEANING BARB/PORT FOR HOSE ON THE INDUCER. And with the hose on the pressure switch but off of the inducer, suck on the hose and listen for the click, meaning it's closing.

Inducer motor may be getting weak and not closing the pressure switch.
 
#3 ·
Thanks for your reply.

Yes, with the hose off, the furnace runs fine. That's how it is running right now. I am not comfortable with it, but I need a warm house.

I have tried cleaning the barb on the switch by sticking a paper clip in and out a few times. I have sucked on the hose with it attached to the switch and I do hear it closing. Also when I stuck a paper clip in I pressed it and heard a click as well.

The only part of your reply I am not sure of is the hose to the inducer. Is the inducer the black fan/motor to the right of the switch and under the burner box that vents up and out? I don't remember there being any hoses or barbs on that unit. I am at work now but I will look and try when I get home.

The only hose I have cleaned and that is unhooked right now is the one that run from the switch to the burner box (and there is a T in the middle of it and a hose that runs to the gas valve vent).

If it is a weak inducer motor is there any possible fix for this besides a replacement? Like, could there be a belt or pulley slipping or would a furnace cleaning help?
 
#4 ·
Yes, the inducer motor is the what vents the exhaust fumes out through the metal flu pipe. The hose should be attached from said motor to pressure switch. I'm not sure what this 'T' is you're speaking of is. Can you take some pictures?

From here it sounds as if someone has bypassed something.
 
#8 ·
Mine does not look like this - I will take some pictures and post.

If it exhausts fine, how could the intake be plugged? On the outside of the house it all comes in/out one/the same vent. The pressure is really good on the exhaust and looking in I did not see anything blocking it….
 
#6 ·
Hi
I was hoping someone could help me. I have a 6 year old Trane XR90 Furnace that blinks 3 red lights when it calls for heat, then it shuts down.
3 Red Lights means “Pressure Switch Error”.



This is what I have tried to fix this.


· I have unhooked the hose that runs from the switch to the gas valve and to the burner box and cleaned the hose. I have also cleaned the barb the sticks out of the burner box.
· I have checked all the clear drain hoses in the furnace to make sure they are attached and not pooling water.
· I have checked my outside vent – it is not blocked and it exhausts when the furnace runs.
· I have installed a new furnace filter.


Here is some history. This has happened in the past (last year and the year before if I rember right) abd cleaning the barb helped, cause after I cleaned the barb form the burner box when I hooked the hoses back up the furnace worked.


This is not the original pressure switch. When it was under warranty I put a service call in and the first tech that came changed the switch out. But the next tech that came the day later because that didn’t fix the problem found the problem to be the outside vent was iced over. Not sure it this means anything or not just wanted to add it.


Now the weird part, right now the furnace works fine (cycles fine) when the hose that runs from the switch to the burner box is unplugged. But soon as I plug it in it will call for heat and shut down and blink 3 times.


Can anyone help me? Any ideas what is going on?
You have a plugged intake pipe..........DO NOT OPERATE THIS UNIT UNTIL THIS CONDITION IS CORRECTED!!!!!!
 
#20 ·
the confusing thing is that from what you are saying, the unit is running and functioning properly with the hose detached from the pressure switch. the only thing i can deduct from that is that the pressure switch is somehow "stuck" in the closed position, because without a vacuum it would stay open and thus disable the unit. removing the hose under normal operating conditions would cause the unit to NOT run. if it IS running, i would think the pressure switch was the obvious problem.
 
#22 ·
its not confusing at all.............the hose that is detached monitors the burner box for proper air flow for combustion.......take of the hose and take away the control boards ability to monitor the intake air.........hence a plugged intake...............i would be a dollar that if he put the hose back on, and took the burner box door off it would run as well.......if you have spare time.......check the cap.............
 
#27 ·
the trap is easy to find, follow the condensate hoses into the blower area.....its white with 2 5/16 screws holding it in place.two clamps hold the hoses on......when i clean these i submerge them in a bucket of bleach/water (as hot as you can stand) along with the hoses, as they too can get a build up in them. the off white fitting attached to the base of the combustion motor is another well know choke point on trains, so remove and clean this fitting as well.

after saying all this I do not think that its a trap issue......but what I described is good annually maintenance.
 
#30 ·
Clogged/restricted pressure hose. Restricted exhaust or combustion air intake pipe. Corrosion build up on hose pressure ports. Restricted drain line. Crack in a pressure hose. Slow spinning inducer. Cracked heat exchanger. loose restricter plate on the back of the inducer.

The tech should use a manometer and see how much pressure the switch is seeing.
 
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