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Tom Scott 11-15-2011 11:30 AM

Trane XR90 - 3 Red Lights
 
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?

Doc Holliday 11-15-2011 11:58 AM

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.

Tom Scott 11-15-2011 12:14 PM

Quote:

Originally Posted by Doc Holliday (Post 771681)
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.

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?

Doc Holliday 11-15-2011 12:39 PM

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.

Doc Holliday 11-15-2011 12:41 PM

See the hose from the inducer to the switch?

http://0.tqn.com/d/homerepair/1/0/t/...nt_inducer.jpg

harleyrider 11-15-2011 12:45 PM

Quote:

Originally Posted by Tom Scott (Post 771657)
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!!!!!!

Doc Holliday 11-15-2011 12:48 PM

Geez Harley, you could've warned us to put on some shades... :laughing:

Tom Scott 11-15-2011 01:09 PM

Quote:

Originally Posted by Doc Holliday (Post 771707)
See the hose from the inducer to the switch?

http://0.tqn.com/d/homerepair/1/0/t/...nt_inducer.jpg

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….

harleyrider 11-15-2011 01:14 PM

Quote:

Originally Posted by Tom Scott (Post 771732)
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….

its either the intake or the drain...........removing that tube is no different then by-passing a tripped limit......you are risking possible ,fire, carbon monoxide poisoning and death by tampering with that hose., take my advise and shut that unit down and get a pro out there.It could be a bad switch, but they rarely fail.

Tom Scott 11-15-2011 02:27 PM

1 Attachment(s)
Here is a picture

Tom Scott 11-15-2011 02:31 PM

Well this is starting to look like a call to a tech.
I have C0 detectors installed on all levels of my home or I wouldn't even run it like this

Doc Holliday 11-15-2011 02:54 PM

Check that run capacitor on inducer motor.

Tom Scott 11-15-2011 03:00 PM

Quote:

Originally Posted by Doc Holliday (Post 771805)
Check that run capacitor on inducer motor.

Is that the thing on the top left or bottom right on the motor and how do I check it?

Doc Holliday 11-15-2011 03:09 PM

Left. Silver can looking thing with two wires on it. Need meter with mfd or just remove it and take with u to Grainger. Ten buck part.

Doc Holliday 11-15-2011 03:13 PM

Bottom right is 120 volt feed to inducer from board.


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