Time for help: Furnace vacuum switches


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Old 11-12-19, 07:02 PM
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Time for help: Furnace vacuum switches

Hello. I have been having some trouble with my fridgidaire gas furnace off and on for about a year now. I am having trouble getting the condensate vacuum switches to close and stay closed.

Here are the symptoms. When the thermostat calls for heat the draft inducer motor starts as it starts I can hear the vacuum switches that are plumed into the motor itself click closed. I can also hear the vacuum switches that are on the "condensate" part of the furnace close and open and close and open. If they stay closed the furnace will fire and will usually run until the thermostat is satisfied. If the condensate switches do not make the furnace shuts down and tries a restart again in about a minute. Sometimes the switches will close long enough for the flame to run but will break as the flame is running so the furnace shuts down the flame.

I have cleaned out the nipple on the condensate pan that the rubber tube connects to. The first time I did this it was plugged and I could feel the tool I was using break the crud out. The furnace ran great for months after this.

I have checked to see that my draft inducers is pulling the correct amps. It is pulling about .4 and it rated for .5. So that seems OK. It spins freely and there are no noises. I even took it off to see if the fan is dirty. It is clean as a whistle.

I checked the condensate drain to see if it is backing up water. It is not. It is flowing fine.

I checked to see if the intake and exhaust pipes are plugged in any way. As far as I can tell from the ground they are not but I have not gone up there (on the roof) to really check em out. I can't pull the exhaust pipe off in the basement to test without it on as the pipe is plastic and it would be difficult.

Other than just buying new vacuum switches, what are my options? I am getting to the point where I am not comfortable leaving my house for long as I dont know the furnace will work.

I posted what I thought were some relevant photos. You can see from the screenshot of our wifi thermostat that is calling heat for long periods of time and the temperature inside drops.
 
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Old 11-12-19, 07:31 PM
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FYI...... that is an improper gas connection. CSST is not allowed to penetrate the cabinet. It should be hard piped to outside the cabinet. Is there a gas valve there for servicing ?

Take the gray hose off the inducer. Using something very small like a drill bit or straight pic.... clean the tiny hole all the way inside the hose barb fitting. What ever you use to clean the hole must penetrate into the blower area.

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Old 11-13-19, 07:11 AM
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Thanks for the tip on the CSST. I do not know off the top of my head if there is a valve close by. I know the line runs in black pipe until about 3' from the furnace and then it runs in using the CSST.

The vacuum switches I am having a problem with are not plumbed into the housing of the draft inducer. Those switches are working properly. The switches that are not working are in the 4th picture. They are measuring the vacuum in the black box immediately behind them. I am guessing that is the condensate area as that is where all the water is flowing out of. If you look closely you will see the grey tube that comes from the switches and then plugs into the black box.

I did have success cleaning out that tube connection with a safety pin once and that fixed my problem for a month or so. But now that is not the problem I am having any more.

If I had to guess, I'd say the draft inducer is not pulling as much vacuum as it use to. Either the motor is getting weak or there is some type of blockage. But I dont know where else to look. I took the motor off and it was perfectly clean.

Do the motors ever just get weaker?
 
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Old 11-13-19, 08:55 AM
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Probably dirt build up somewhere.
Those pressure switches are mounted on the collector box. They don’t measure condensate specifically but are piped into the wet exhaust air.
The switches themselves could be faulty. A manometer can be used to verify.
 
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Old 11-14-19, 05:58 AM
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I was able to check last night and I have a service shut off valve in the black pipe right outside the furnace cabinet. Right after the valves the csst starts and goes into the furnace.
 
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Old 11-14-19, 06:05 AM
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roughneck- I ordered a manomoeter. It should be here in a couple of days.
 
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Old 11-21-19, 08:32 AM
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I received the new manometer the other day and was able to test the vacuum in the condensate area last night. It is pulling right at 1" of water column. The vacuum switches I have hooked in there are .9" and .8". There are two of them as it is a dual stage furnace. I don't know how much safety factor there is supposed to be between vacuum measured and the limit on the switch but, I have more vacuum than the switches are labeled to need so I feel like I am good.

The thing is, ever since I posted below that I am having trouble. The furnace is working perfectly. It has not had one miss. I cleaned out the vacuum nipple on the condensate area before I put it all back together and ordered the manometer so maybe when I did that I cleaned out some gunk.

I have no idea what else it could be it seems to be working perfectly. If it starts acing up again I will post back here.
 
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Old 11-26-19, 04:54 PM
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monitor the vacuum and see if it drops when the switch drops out. monitor every switch that could be be culprit.

if switch drops out with normal vacuum, it's bad.
 
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Old 11-27-19, 06:14 AM
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Bought new vacuum switches

I have been watching my thermostat to see when the furnace drops out. It continues to drop out for periods of time but it always kicks in again before it gets too cold in the house to notice. For example, on monday the thermostat called for heat for two straight hours. Eventually, after two hours of trying the vacuum switches made and it started and heated back up. By the time I got home from work, everything was running fine and the furnace was starting on the first try. It has been working since.

I went up on the roof to check the vents. They look fine. I checked the vent to see if maybe there is a sag in it causing water to build up. I dont think that could be the case because the installation runs down hill when horizontal and it only runs horizontal about 4'. I checked the vacuum with the manometer on Monday and it was pulling 1.4". Because the switches make intermittently. I have not actually been able to measure the vacuum during a time when the switches are not working.

I finally bit the bullet and bought a new set of vacuum switches. It is a dual stage set up so they are rated at .8" and .9". Seeing as I am measuring 1.4" they should make quite easily. They were about $50 w/ delivery and tax. I will keep this thread updated in case anyone else is having similar issues.
 
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Old 12-05-19, 09:12 AM
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I put in the new vacuum switches and as you might have guessed that did not fix it. I started doing a bunch more research and found post #9 here:

Nordyne FG7TC 060D-VB short cycling

I cut, rolled, and inserted a straw into my condenser vacuum port to see if maybe water is dripping in there an causing my intermittent issue. So far the furnace is running perfectly. I will keep you all posted.
 
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Old 12-09-19, 11:52 AM
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Solved

I can confidently say that my furnace is fixed. It has not missed on cycle since last Wednesday. As I mentioned in the post below I fixed it with a simple piece of straw. Who would have thought?

If you have a similar furnace make sure to read my previous posts on a solution this was a tough one to figure out as it was intermittent and there were no codes.
 
 

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