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Old 09-21-2010, 09:38 PM   #1
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Luxaire Furnace problem


I have a Luxaire model PBLU-LD12N080A furnace with the following chronic problem. After about 2 days of running, the pressure switch which senses the exhaust fan being turned on will fill with condensation and will cause an ignition failure. Once I empty the water out of the switch and reconnect it, everything works for another 1-2 days. Is this a faulty design or is there some way to prevent the condensation from building up in the switch. I've had two different techs look at it, but they don't seem to know how to fix it. I've tried putting in a tee on the hose from the blower to the switch, and I've also cleaned out the condensate trap in the furnace, but nothing seems to work. Could use some advice on this.
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Luxaire Furnace problem-img00124-20100922-0649.jpg   Luxaire Furnace problem-img00126-20100922-0650.jpg  

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Last edited by Orlo; 09-22-2010 at 10:16 AM. Reason: Photos added
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Old 09-21-2010, 09:49 PM   #2
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Luxaire Furnace problem


Post a pic of the switch and hose and how it drains to the header box or trap. Hose should have NO traps in it. Should drain down with no sags, kinks to the trap or collector box.

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Old 09-21-2010, 10:10 PM   #3
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Luxaire Furnace problem


if that's an 80% faf..;.maybe someone's vented it incorrectly causing too much condensation
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Old 09-22-2010, 06:39 AM   #4
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Luxaire Furnace problem


The run for the vents (exhaust and makeup) are about 30' long. Could this be the problem? If so, what is the recommended maximum distance for the exhaust?
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Old 09-22-2010, 07:05 AM   #5
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Luxaire Furnace problem


I'll post pictures later today. I removed the tee and drain. The switch did not have a drain from it. I added one to see if it would help get rid of the water condensation... didn't work. There are two ports where water can be drained from the exhaust fan - one near the top of the exhaust leg and one at the lowest point on the fan. The one which was used when the furnace was installed (and still is today) is the one near the top of the exhaust leg. I've tried connecting the drain to the lower port, but the problem still occurs. The condensate trap is clean. After the furnace runs for extended periods of time, there is a considerable build up of condensate in the bottom of the fan. I know this because when I tried to connect the drain to the lower port on the exhaust fan, a lot of water drained from the fan. This leads me to believe the exhaust vent may be too long (~ 30').
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Old 09-22-2010, 07:57 AM   #6
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Luxaire Furnace problem


can you post a pic of the vent ? The water should drain from the fan housing into the condensate box. I would check for blockage. With hose removed . does water come out of the fan housing ?

Last edited by kenmac; 09-22-2010 at 11:19 AM.
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Old 09-22-2010, 10:19 AM   #7
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Luxaire Furnace problem


The run is mostly horizontal - approximately 30 feet with a total vertical rise of about 3 feet.
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Old 09-22-2010, 05:19 PM   #8
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Luxaire Furnace problem


Check if the pressure switch port has a small hole in its port near the body. If so, make sure the hose is NOT covering it. If its covered, the switch will draw the water up the tube.
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Old 09-22-2010, 06:55 PM   #9
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There is no hole in the port.
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Old 09-22-2010, 06:59 PM   #10
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Luxaire Furnace problem


Next time you have the furnace running, check the incoming air temp, and the supply air temp, make sure it is atleast 40 degrees hotter leaving the furnace, then it is entering the furnace.
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Old 09-23-2010, 07:50 AM   #11
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Luxaire Furnace problem


Will do. Generally, the supply temperature is whatever the OA temp is because it is piped with an OA supply line. I haven't measured the supply air temperature, but I would guess that it is in the range of 90 - 100 F. During winter operation this would give a delta of 60 - 70 degrees. The pressure switch fills with water in about 2 days with the furnace running on a typical winter day (OA = 30 F).
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Old 09-23-2010, 07:56 AM   #12
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Luxaire Furnace problem


Here are some more pictures. The drain from the blower is connected to the outlet side of the exhaust. I tried connecting it to the port on the bottom of the blower (shown in one picture), but it didn't help.
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Luxaire Furnace problem-bottomplug.jpg   Luxaire Furnace problem-drain2trap.jpg   Luxaire Furnace problem-drainfromblower.jpg   Luxaire Furnace problem-drainline.jpg   Luxaire Furnace problem-trap.jpg  

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Old 09-23-2010, 08:16 AM   #13
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Luxaire Furnace problem


looks like that hose needs to be connected to the lower port on the vent motor. With the furnace in operation.( when your having this problem ) Have you pulled the plug at bottom of the motor to see if water runs out ?? there should be small amount of neg. perssure on that switch. So, it can't be sucking water into the switch

Last edited by kenmac; 09-23-2010 at 11:07 AM.
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Old 09-23-2010, 01:22 PM   #14
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Luxaire Furnace problem


I agree that the water shouldn't be coming from the pump because of the negative pressure, but when I drain the water from the pressure switch, it comes from the port that is connected to the vent pump. Since the pressure switch is just a diaphragm, I don't think the water can pass from one side of the diaphragm to the other (I only get water from the one port). This is driving me nuts. I can't understand where the water is coming from. In response to your first comment - yes, I do get water draining out of the vent pump when I take the plug off the bottom port. But if the water isn't coming from the pump, could it be condensing inside the pressure switch?
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Old 09-23-2010, 06:01 PM   #15
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Luxaire Furnace problem


I was talking about the return air from your house, and the supply air to your house. Not the intake and exhaust for combustion.

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