Trane XR90 Pressure Switch Error

kenk

Hi, I was hoping ya'll could give a little advice. I have a Trane XR90, installed aprox '03-'04. I have owned the house for 1.5yrs. The furnace ran great all last winter. This fall, ran great until it got real cold(20's and below). Then one day I heard the transducer cycling on and off with no full heat cycle.

Found the LED blinking 3 times- pressure switch error. And after a quick google search, found this is a somewhat commom problem with no set fix. Almost something different everytime.

I checked the obvious myself, intake and exhaust pipe not clogged,pipe slope, drain clear, etc. Found nothing, except that it ran great with the intake unhooked at the furnace, drawing inside air.

So i called a local service guy. They double checked everything I did,found nothing. Said I had a bad pressure switch. They replaced it. Ran great for a week. Then same thing.

I called my local Trane Service Center. He recommended trying to shorten the intake and exhaust pipe- its 2" dia pvc with a total lenght of aprox 12-14', or step up to 3" pipe.

The reason I called was to get a price on a transducer,which i thaught might be getting weak, hense why it runs great with no intake vs a 12-14' intake. But the service guys tested it, said its ok.

Any thoughts or ideas or suggestions would be greatly appreciated

beenthere

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.

kenk

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...

Tator1076

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.

Marty S.

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.

kenk

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

yuri

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.

Tator1076

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

Tator1076

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

yuri

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

Tator1076

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.

Tator1076

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

Tator1076

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

yuri

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.

kenk

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