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Direct Vent Furnace Draft Inducer

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Old 07-20-2009, 08:12 PM   #1
Armstrong Carpentry
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Direct Vent Furnace Draft Inducer


Im a carpenter so im a little out of my league with this stuff.

I had a service tech come out to make a repair attempt but after repair did not work and the guy would not return my calls. I started looking at it myself.

I have a Cozy HEDV404

The problem was the pressure switch would not close (3 blink), so the tech replaced the switch (with a totally different looking switch although it was still 2 hose, 2 wire it was about 1/2 the size) - anyway it didnt work.

I started looking at it myself - if I plugged the hose on the burner side the furnace fired up, If I sucked slightly on the blower side I could get the furnace to fire up, it would also fire up with the switch jumped. So I think I eliminated the switch...

Took all the vents appart and checked for obstructions and then I started looking around the inducer for air leaks, there was some rust on the base of the furnace under the inducer blower (thinking condensation). I pulled the assembly out, the gasket was toast and fell apart. I cleaned it all up and used a high temp silicone to re-asemble. Let set up overnight... Suction was much louder on the inducer side (rubber tube) but the furnace would still not fire.

Next I noticed a screw on the pressure switch (allen screw) - turned it about 1/4 to 1/2 turn counterclockwise and the furnace fired up, tested it a few times since and it seems to fire up normally - I will block the vent next time I run it to verify it shuts down with the pressure switch.

My questions:

Could the leaking gasket have caused the pressure switch failure?

Has anyone used "red" high temp silicone to replace a gasket on one of these blowers? Will it hold up?

Has anyone adjusted a pressure switch?

Thanks in advance for any ideas or coments - with winter coming I need to get on this...
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Old 07-20-2009, 09:43 PM   #2
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Re: Direct Vent Furnace Draft Inducer

There is a few things you may want to check, gaskets could be it. intake/ exhaust obstructions . heat exchanger cracked? You will need to test the draft to see how much you have against original switch rating. test the old switch to see if it closes under correct rating.


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Old 07-21-2009, 10:50 PM   #3
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Re: Direct Vent Furnace Draft Inducer

You can use RTV sillicone as a substitute for the gasket. One thing you might want to do is to ream the nipple on the furnace with a paperclip to clear up any obstruction. The nipple is the part that one side of the vaccum hose attaches to on the furnace. It's possible that there is crud inside of there. That crud is a by-product of combustion. If you want a more detailed answer for why the crud buildup, feel free to ask, but for now, just use a paper lip to make sure that the inside of the nipple is clear.
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Old 07-22-2009, 05:46 AM   #4
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Re: Direct Vent Furnace Draft Inducer

Pressure switches come factory adjusted. If the furnace fails to fire due to pressure switch not closing the draft should be tested using a manometer tee'd into the hose going to the pressure switch. If the draft is correct, higher than the pressure switch make setting and it is not firing then the switch is at fault. If the draft is below or near the make setting of the switch then the draft is incorrect.

Causes of incorrect draft. Lack of combustion air, mechanical room depressurizing; improper venting, unit heaters though vented and terminated side wall may actually need to be extended vertically. Wind conditions may actually prevent the switch from making by putting back pressure on the vent when terminated next to the wall. Heat exchanger leaks. Draft inducer slowing down in rpm either by bearing drag or a lower voltage being applied. Just because the draft motor is running does not mean that it is receiving full voltage. Lower voltage will result in a slower speed and thus a lower draft. Inducer fan blade impacted with dirt or the blades have eroded down to a smaller surface area. Debris covering the area where the hose barb connects. Running a small drill bit or solid wire through the hose barb can break the debris loose and improve draft. Pressure switch hose: If the hose is dried out and cracking then it may not be sealing properly. These can be replaced with a section of high temperature silicone tubing available at most auto supply stores.

The allen wrench adjustment should never be adjusted in the field unless you have a draft gauge to verify that it is operating and contacts making at the correct pressure. Just as you not adjust burner gas pressure without using a gas manometer. To do so would allow the unit to operate outside its design parameters.

Last. Check the flue gases with an electronic co/combustion meter to ensure that the unit is burning properly and that high levels of Carbon Monoxide are not being produced.
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Old 07-26-2009, 11:45 AM   #5
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Re: Direct Vent Furnace Draft Inducer

flash probably nailed it...ventor to pressure switch is hose. pull hose off of ventor port and push some small pin like object in there to clean unless u have a magnahelic to reset switch correctly ,throw it out and buy proper one.the switch was doing its job no adjustment ever
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