DIY Home Improvement, Remodeling & Repair Forum > Appliances > HVAC > Trane XE80, it is not the pressure switch




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Old 12-07-2011, 10:38 AM  
pookie16
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Default Trane XE80, it is not the pressure switch

I posted a reply on another thread and did not get any response, so I am starting a new thread.
I think I read all threads on this topic as I thought I had a similar problem. I get the three blinking lights after the furnace works for a few hours every day and I 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 take it off and even just 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?



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Old 12-07-2011, 09:01 PM  
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it sounds as though the vacuum is borderline. You can not find this out for sure without a manometer. However, you need to check your flue. It may be partially blocked.



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Old 12-07-2011, 09:54 PM  
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Thanks for the reply, but I want to ensure that the switch would work in a way that seems counter intuitive to me.
So even though if I take the hose off and hold the hose close to the inlet of the switch and it will work every time, you think it sounds like not enough vacuum? I was thinking that is lots of vacuum if there is enough to overcome the major leak of not even having the hose totally attached. How much vacuum do I need if I get a manometer and test it? A few inches of water?
I am not sure why it will always work if I turn it off and then on, if it was a vacuum problem. If there is an instance of not enough vacuum once, does that prevent the switch from closing until you let it open (by releasing the vacuum) and then reapply the vacuum? I will check the flue and let you know. I will not have access to the furnace for a few days as I am out of town.
Thanks

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Old 12-08-2011, 07:35 PM  
paul52446m
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Default Trane XE80, it is not the pressure switch

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Originally Posted by pookie16 View Post
Thanks for the reply, but I want to ensure that the switch would work in a way that seems counter intuitive to me.
So even though if I take the hose off and hold the hose close to the inlet of the switch and it will work every time, you think it sounds like not enough vacuum? I was thinking that is lots of vacuum if there is enough to overcome the major leak of not even having the hose totally attached. How much vacuum do I need if I get a manometer and test it? A few inches of water?
I am not sure why it will always work if I turn it off and then on, if it was a vacuum problem. If there is an instance of not enough vacuum once, does that prevent the switch from closing until you let it open (by releasing the vacuum) and then reapply the vacuum? I will check the flue and let you know. I will not have access to the furnace for a few days as I am out of town.
Thanks
Pressure switches are used different way's. Some furnaces have two switch,s, some have one with two hoses and some have one switch with one hose. If you have one switch and one hose, when you pull off the hose or turn off the power and back on, the unit has cut out on safety and you are recycling it. You say it runes for a few hours then turn off . This sounds like the drain not working right. it builds up with water in the heat ex changer and the pressure switch turns it off. After it set for a while, it drains out and you recycle it and it starts back up. Sounds like your drain it working, but not good enough. Paul
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Old 12-08-2011, 07:40 PM  
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Pressure switches are used different way's. Some furnaces have two switch,s, some have one with two hoses and some have one switch with one hose. If you have one switch and one hose, when you pull off the hose or turn off the power and back on, the unit has cut out on safety and you are recycling it. You say it runes for a few hours then turn off . This sounds like the drain not working right. it builds up with water in the heat ex changer and the pressure switch turns it off. After it set for a while, it drains out and you recycle it and it starts back up. Sounds like your drain it working, but not good enough. Paul
The only problem is the title of the thread states that it is an 80%
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Old 12-09-2011, 11:58 AM  
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I agree with this last post. At first the idea of water building up made sense. I have never seen any drains on any furnaces I have owned, and I do not see one on mine. I know it is not hooked up to the sewer system and there is never any water on the floor, so I suspect the 80% furnaces do not drain.

So then, what else could it be? I did a test of turning the thermostat down and up to see if that cleared the error signal (those 3 flashes) but it did not.

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Old 12-09-2011, 12:06 PM  
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And back to the low or intermitent vacuum. I agree that this could be a problem, but I still don't know why just pinching the hose would make the furnace start. If it is a case of intermitent vacuum, then the symptoms should be the same as pinching the hose (removing the vacuum and putting it back). What am I missing here? Oh and if I test the vacuum, how much should there be?

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Old 12-09-2011, 03:28 PM  
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I tested the vacuum - 200Pa or 0.75in H20. Is that good or bad?

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Old 12-09-2011, 03:44 PM  
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I tested the vacuum - 200Pa or 0.75in H20. Is that good or bad?
It depends on what your furnace pressure switch calls for. sometimes its listed on the switch, other times you have to call the manufacturer.
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Old 12-09-2011, 10:38 PM  
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Is it possible that the pressure switch has to open at some point in the cycle? What if the induction blower stayed on sometimes when it was supposed to be off. This would not allow the pressure switch to open and then the cycle would not start. Me pinching the hose to the pressure switch allows the switch to open and then close again when I release it. Is this possible and if so, what would keep the induction blower running?



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