What size furnace.

Check to see if there is moisture inside the hoses that go to the pressure switch.

14' is not a long run.

 

80k btu. The people that replaced the switch said the lines to the switch were clear, but i'll check again. I know condensation occurs in the exhaust pipe- but it litteraly runs out. But I didn't find any pooling.

Luckily it is rated for singe pipe use, so I can run it with the intake off. It just baffles me why it runs great like that...

 

Pressure switch really dont go bad. I first check if you hear water in the pvc pipe. I also check the tube from pressure switch tube that goes to Draft motor. Pull that tube from the draft motor and you will see that hole. Then take a paper clip and take it in and out of the hole. You may even just try with blowing in that tube that goes to draft motor. Alos if the burner are in a burner box then you will see the a tube goes off the side the box make sure that is clear too.:thumbup:

 

Have anything outside that could cause the exhaust to recirculate into the intake? Seen many a garbage can, grill, bush and a host of other things placed in front of the pipes to cover them from view and it causes problems every time.

 

Thats exactly what I thought about the pressure switch, its sensing a pressure difference,and tripping. But they insisted on giving me the pleasure of paying to replace it.

I checked all 3 tubes going to the pressure switch, they are clear(no water). Although the 3 are from the burner box,pre burners, the heat exchanger,post burners, and the gas valve- none come from the tansducer motor itself. For a minute I thaught maybe too high gas pressure, but that wouldn't explain the running with intake unhooked, not running with.

The intake/exit is a concentric cone. Its on a corner of house where theres nothing around it. I pulled the centering ring off to look down the intake,as far as i could, and just had some minor cobwebs and stuff. Cleaned 'em out but didnt make a diff.

I might take a plummers snake down the intake, or cut it in half, just to be sure nothings in there. Can't tell by looking cause it takes three 90 deg bends

 

Check where the intake pipe attaches to the furnace or burner box. LOTS of furnaces have a screen there and it can get plugged with debris.

 

I had a couple dead grasshoppers, but nothing like leaves or grass

 

Take the tube off the burner box and turn back on ( just let it hanging) see what happen

 

Note did you check to see if the Fan limit been trip becasue no matter what if that trips it will kill 24 volt to pressure switch . That is all vents open in the house, filter clean and fan not running hot

 

If it's tripped, would it set off a code to the LED?

 

Do you know what that tube does, Guy? It regulates the gas valve. Remove it and the unit will overfire!!

 

Yes but if the barb fitting is blocked it will not fire.

 

Note too you can go outside to fresh air and put your hand on the open part and see if it sucking you hand. If so you r pull good air if not you have a block.

 

It's hard to tell how well its sucking outside, having a round concentric in/out. Its sucks from behind the cone, 360deg. But i can feel it pulling air.

 

hey is one of the tubes go on a black cover plate front of the heat exchager if so clean that hole out with paper clip. because crap from the water plugs that up time to ime not letting the pressure switch ,make

 

I won't run you down but it will fire with the hose off or that fitting blocked. Gotta be careful on this site or you will get corrected. Especially if people give dangerous or incorrect advice.

 

Yes sorry I wanted to delete that part after i post it. Did u go outside check fresh air intake and did you check that part on black cover plate ( front of heatexchager)

 

Make sure the concentric kit exhaust pipe (inner one) is pushed in properly. It can get disconnected internally in the kit and cause the exhaust to recirculate into the intake pipe and trip the switch. Push it and the donut piece in firmly. May have backed out an inch from expanding/contracting.

 

Those cone really dont get pluged but if push back may cause low air flow

 

The exhaust pipe needs to mate/seat internally in the kit. If not the exhaust will get sucked into the intake. Cannot push it in too far to block airflow, impossible. On some of them you can pull the exhaust pipe out if the installer did not glue it together. I have had debris 2-3 feet inside the kit and iced up internally.

 

well, i took a small piece of wire and ran through the barbed fitting on the intake box/burner box/whatever it's called, that the intake pipe attaches to,then used the hose to blow it out. Then theres a hose off the back of the pressure switch, i cleaned out the fitting that hose goes to(looks like the heat exchanger) But didn't mess with the hose or fitting going to the gas valve.

I hooked up the fresh air intake, and it ran through a complete heat cycle with no prob's.

 

Ok just keep cycling it. If it was the one that goes to heat exchanger. you need to clean that time to time.

 

Probably the hose port on the collector box/heat exchanger got partially plugged. Happens a lot on Carriers,gets a sulphur deposit there. Check your concentric kit like I described annually. Glad you got it going.:thumbsup:

 

As far as the intake/exhaust outside, you're right. you cant push it too far back, there's tabs that stop it from going too far. The center exhaust pipe is seated correctly, flush against the face.

But being I cant see too far in either end of the intake pipe, I am wondering if something ain't in there. Damn whoever put that many bends in it.

 

As far as the intake/exhaust outside, you're right. you cant push it too far back, there's tabs that stop it from going too far. The center exhaust pipe is seated correctly, flush against the face.

But being I cant see too far in either end of the intake pipe, I am wondering if something ain't in there. Damn whoever put that many bends in it.

No Not move it. If It still cycling promblem is solve go get a beer and wach some t.v. lol

 

Try CAREFULLY pulling it out and look inside for debris. Don't yank too hard. Some guys glued that pipe in and it won't come out. Is supposed to be pressed in firmly after being cut to the proper length and is a tapered compression fit internally. I de-iced one in -30F for 3 hours and can write the book on them.:wink:

 

Yea, its glued in. you can see it at all the joints.

Well, been cycling ok so far, knock on wood. Thanks for the quick help and ideas:thumbup:

 

Gas Valve XR90

Is the Gas Valve actually "regulated" by the Black Hose going to it? I actually measured the W.C. and it was about -.5 wc. The other side of the pressure switch was about -1.7 " WC. The switch says it's factory set at 1.29". My furnace runs fine with the small black hose disconnected from the pressure switch. If I blank that hose, the gas valve is still connected to the fire box so what is the purpose to begin with? ...:wink:

 

If you have a hose blanked off to the pressure switch to run your furnace. Then most likely, there is something unsafe with your furnace.

 

We had no heat, so we then checked the light indicator on the unit and discovered it was a Pressure switch error. Thinking there was blockage in the intake or outflow PVC pipe, we first started with the vent on the outside of the house. We unscrewed the vent cover and put a wooden pole, like a broom handle, into each pipe and there appeared to be no blockage. We then tested the unit with the metal cover off the area where the burners are and the unit worked, leading us to believe there was a blockage SOMEWHERE, maybe close to the area at the top of the unit where the PVC pipes were connected to the unit. This involved cutting the intake PVC pipe with a hacksaw so we could check for blockage. Sure enough, an old wasp nest and several leaves were at the base of the pipe, right above the burner area. Vacuumed out the nest and leaves. We bought a a PVC coupling to reconnect the area we split with the hack saw. We put 1/8" hardware cloth over the vent area outside to deter further wasp nests and are back in the heating business.

 

In my case it was a manufacturing or installer defect. The impeller motor/fan assembly is normally held to the chassis by three screws. Turned out, one of the screws (bottom) wasn't screwed in. It was just laying around in the corner of the metal shelf. Over time, the impeller slightly separated from the chassis, leaving a small air gap. This resulted in a pressure differential between inside and outside air triggering the pressure switch error.


I removed the impeller, silicon-ed the mating surface, and reinstalled with all three screws. Has been working without any issues for two seasons now.


Took me a very long time to figure this out, but the solution turned out to be super simple and virtually at no cost. The big clue was opening and closing the window near the furnace - with the window open, no problems, with window closed, pressure switch error.