Trane XR90 Pressure Switch Error - Help Diagnosing

10550 Views 6 Replies 4 Participants Last post by Brian1212345, Dec 23, 2020

dkenne

Discussion Starter · Feb 4, 2018

I have a Trane XR90 furnace that is periodically not igniting. I get a “pressure switch” error (three blinking lights). We have had the issue in the past, but after shutting down the furnace, waiting and turning it back on, it would work normally. This winter, the error has been much more common.

I have been reading through numerous forums and have checked the intake and exhaust pipes, pressure switch tubes, and drain tubes and all seem to be fine. The exhaust tube was dripping water — when it was installed, they didn’t use the purple PVC glue. Not sure what they used, but I took the pipe apart and glued it properly. The furnace worked for about 5 days, but now we are having trouble again.

When we have the issue, the furnace begins the heating cycle — blower turns on, exhaust fan runs and the ignition glows. When the burners try to light, they ignite and then immediately shut off and then it tries to ignite a second time and immediately shuts off. The fans continue to run and the furnace will try to ignite a few more times before we get the two-light code indicating that the furnace has locked out.

I don’t know what’s causing the error. I have found that when the furnace is having this error, if I disconnect the pressure switch tube from the burner box, the furnace will light. Then, if I reconnect the tube, it continues to work without any issues. If I’m understanding what I’m reading in the forums (I’m far from an HVAC expert), if there is a problem with the system, reconnecting the pressure switch tube to the burner box after it ignites should shut the furnace down again?

Any help in diagnosing the problem would be greatly appreciated. I don’t know what else to check on the furnace to diagnose the issue.

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yuri

· #2 · Feb 4, 2018 (Edited)

The proper way to test it is to use a differential pressure manometer and tee it into the hoses for the pressure switch. You need to know the "WC rating of the switch also. Hopefully it is written on the label of it.

Your inducer fan may be just barely producing enough vacuum/draft to close the pressure switch. Playing with the hoses bumps it and sometimes it works. The inducer may be worn or not turning fast enough or you got some blockage in the heat exchanger.

Point is w/o checking the pressure on the switch you will never know. This is some advanced tech troubleshooting so if you are not comfy with it then call a Pro.

Amazon has cheaper meters but I am not sure they are accurate as you get what you pay for and at this price point it is Chineez stuff.

Pros use more expensive UEI and Fieldpiece meters but they are in the hundreds of $$.

https://www.amazon.com/dp/B005FU5HF...ID&pd_rd_r=10EJXEW8471PK1PB14HA&pd_rd_w=9iRZH

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dkenne

Discussion Starter · #3 · Feb 10, 2018

I have a manometer now and I connected it to both sides of the pressure switch. One reads .20 and the other -1.60. I’m really not sure I’m connecting to the right spot. I’ve attached a picture of the pressure switch.

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dkenne

Discussion Starter · #4 · Feb 10, 2018

The pressure switch reads, 1.29 WG on the tag.

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Houston204

· #5 · Feb 11, 2018

The pressure will fall after ignition.
I would get a couple of barbed Tee fittings to allow testing during operation.

I recently had a 90% unit that started up at 1.75" WC but would continue to fall after ignition until it tripped a 1" WC pressure switch.

It had 31 feet of 2" vent pipe but the manual called for increasing to 3" beyond 21 feet.

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dkenne

Discussion Starter · #6 · Mar 12, 2018

I'm still having the same issue with my furnace. Seems to run fine as long as the temperature is below 32 degrees. When the outside temperature is above freezing, but below 50, the pressure switch error occurs. I have a manometer, but I'm not clear on where to connect it to determine if the exhaust fan is working properly. See photo.

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Brian1212345

· #7 · Dec 23, 2020

dkenne said:
I have a Trane XR90 furnace that is periodically not igniting. I get a “pressure switch” error (three blinking lights). We have had the issue in the past, but after shutting down the furnace, waiting and turning it back on, it would work normally. This winter, the error has been much more common.

I have been reading through numerous forums and have checked the intake and exhaust pipes, pressure switch tubes, and drain tubes and all seem to be fine. The exhaust tube was dripping water — when it was installed, they didn’t use the purple PVC glue. Not sure what they used, but I took the pipe apart and glued it properly. The furnace worked for about 5 days, but now we are having trouble again.

When we have the issue, the furnace begins the heating cycle — blower turns on, exhaust fan runs and the ignition glows. When the burners try to light, they ignite and then immediately shut off and then it tries to ignite a second time and immediately shuts off. The fans continue to run and the furnace will try to ignite a few more times before we get the two-light code indicating that the furnace has locked out.

I don’t know what’s causing the error. I have found that when the furnace is having this error, if I disconnect the pressure switch tube from the burner box, the furnace will light. Then, if I reconnect the tube, it continues to work without any issues. If I’m understanding what I’m reading in the forums (I’m far from an HVAC expert), if there is a problem with the system, reconnecting the pressure switch tube to the burner box after it ignites should shut the furnace down again?

Any help in diagnosing the problem would be greatly appreciated. I don’t know what else to check on the furnace to diagnose the issue.

Did you find the issue for this? I'm having a similar problem.

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Trane XR90 Pressure Switch Error - Help Diagnosing

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