HVAC Questions? Ask an HVAC Expert for Answers ASAP
Hi,This is risky business in the blind, not responsible for damages on your end. Click 'accept' when satisfied.. or we can get another expert.
THe problem is most likely in the ignition or flame sensing .or it would not be tying to fire.. if it fires at all, then goes off.. it is most likely a bad flame sensor.. 95% chance of that, little else will case that combination of symptoms....if cleaning it didnt work, replace it
Stay in touch as work proceeds, tell me if the main burner comes on or just the pilot.. if the main burner comes on make sure the flame sensor stays in the flame, if not bend it a bit.
I was hoping that that you would be familiar with my particular model furnace, it has electronic ignition. The ignitor glows white to start the flame. If the flame sensor was the problem, why would the furnace work for sometimes up to 10 minutes?
There are thousands on the market, most run almost identically per type.. sort of like finding a flat tire on a car.. model of the car doesnt affect the diagnosis in most, but not all cases.
I can spend an hour looking each model up or I can ask about a detail or two, thats faster.
If the flame sensor is weak, it will cool off gradually as the draft created by the main burner draws flame away from it slightly.
Make sure its clean. bend it deeper into the flame, get back to me, we can go from there.
Ok, like I said, I have cleaned it a few times already...
It's pretty much directly in the flame.
Find the other end of the flame sensor, that could be at fault in this case.. its in the flame sensing circuit.. replug any wire terminals in that circuit
If it ends at the control card replug all connections at the card. Hopefully its not a bad control card.
Its been a 12 hour day for me, I will be off to bed shortly, See you again in the AM
I've unplugged and plugged the sensor wire several times. Ditto with the connector to the control box. The other end of the connection of the flame sensor goes directly through the heat resistors mounted on either end of the fuel rail. Both heat resistors are fine, and the flame is clean and goes directly into the heat exchanger. I've got a flame sensor on order to get here Tuesday. Space heater should be good enough till then. It's a fairly cheap part, so why not.
sounds like a good plan, just post back when you get it in, Phil
Plugged the new Flame sensor in. It actually worked for the longest period yet. 21 minutes on the first try. Heated the house from 67 to 71 before it flamed out, thermostat was set to 72. System lockout with 2 fast blinks again. Had to let it cool down before the Second attempt ran 3 minutes before flameout. Replaced Controller as well. Checked both Temp Cutout switches immediately after flameout with power off, both have continuity. I'm stumped.
Oh, and I wrote in error that the Flame Sensor wire is in line with the Heat Resistors as I called them, but they are Fusible Links. The Flame sensor wire goes right to the connector that plugs into the control box.
Thanks for the information.
That is going to require a field tech and he may have to take a bunch of stabs at it... call a shop that deals in Trane equipment.
Do you need some Trane numbers in your area? If so tell me which city
I'm going to try to talk to the shop that took my 96 bucks for their "diagnosis", and see if they can send somebody else who has a bit more experience. I've got a couple of numbers from the Trane site. To me, it seems like a temperature related issue. I noticed on the wiring diagram that both the Blower Fan Motor and the Vent Motor have internal Thermal protection. But still, why would they continue to spin after flame out if they were thermally protected. I would think once the temperature got too high, the motor would shut off.
Ok, here's the latest. The same shop sent an older Tech with more experience. I was not able to be home when he did his work. He said one of the Temperature CutOut switches was getting tripped. Now I checked both, and neither was tripping when I checked them. He said basically we need a new furnace because the heat exchanger is overheating. It's odd, because, it trips much quicker when I operate it in first stage only. When I operate it in two stage mode, the second stage will come on after 10 minutes and run for 10 minutes more before tripping.
So they're pushing us to get a new furnace for about $4300. When I mentioned that the A-Coil below the furnace might be clogged up, and could be the cause of the problem by impeding air flow over the heat exchanger, he poo poo-ed me and said the furnace should just be replaced. I'm going to recheck the Temperature CutOut switches later tonight.
Hello again, The evaporator coils clogg up with a matt of hair, fibers, and dirt without fail no matter how clean the filters are kept.. all will have some visible material stuck to the upstream face of the coil after a year.. after 5 years it will be significant or worse, and after 10 years the coil will be restricting well over 50% of the air flow or worse.
The exception would be if you had an elecronic air filter installed and maintained.. $4.000 item, few homes have them... or 2" or 4" pleated furnace filters, maybe 1% of homes have those,
Regards XXXXX XXXXX protection on the fan motors.. and the fact of fan control by thermal devices.. you have that a bit sideways.
The thermal protection INSIDE motor will only trip if somehing is wrong with the motor..its there to prevent fire or more severe motor damage most never trip in their lifetime.
But, the fan motor does cycle in heating mode on a heat sensitive thermostat the only lets the fan run in heat mode when the furnace plenum is warm.. that will cycle the fan many times a day.
Let me know, we can go from there if necessary, Phil
Well, I did verify that the Temperature cutout switch in the Burner section was getting tripped. I basically had to shut the furnace down right after the switch got tripped otherwise it would cool off and reset back to normal quickly.
I've decided to have an HVAC guy clean the A-Coils on Tuesday. I got a bunch of quotes for that . From $250 to $650. I think I'm in the wrong business. These HVAC guys get paid more on an hourly basis than the guy who designs these systems.
$250 is a good number for a through job cleaning the coil,, there other number goes to pay the persons hotel bill in Bermunda.
If you appreciate the help please click the
Accept button its how I get credit, Thanks, Phil
The latest: Had another company come and diagnose the problem. The A-Coil was inspected, and was pristine. After 16 years. Pristine. The Tech homed in on the hi pressure valve. He discovered spiders living inside the tubing and blocking it off. He actually sucked a spider into his mouth by mistake. For now, it looks as if this might have been the problem. I'll keep an eye on it today, and see if the furnace is still working properly.
Hello again... thanks for the feedback. The coil is about as far from pristine as it can get.. thats an educated 'guess' after 50 years in the business. What occured is that the tech removed the front cover of the coil box, accessed the A coil and looked the visible down stream side of the coil.. and noticed that it was pristine.
The downstream side looks good forever.. it is the upstream side of the coil, visible only from underneath the coil that will be matted with every form of lint, hair, air polution solids know to man.
You might call his company and let them know what Ive said.. let me know how that goes.
A dirty coil can drive your heating and cooling costs by several hundred percent...depending. if its only moderately dirty 50% is a good number.
If the coolling coil sits on top of the furnace, inspecting the bottom side of it, the air inlet side, requires removing the furnace or sheet metal work to lift the coil in about 1/2 of the cases. In other cases there is an A shaped panel in the end of the coil that allows access to the inlet faces of the coil.
Stay in touch, Phil
Hi Phil, I was not home at the time of the inspection, but my brother in law was there. The inspection was done with a camera on the burner side of the A-Coil. The Furnace is mounted on top of the of the Air Conditioner and is installed as a downflow unit, so the junk would be on top, or the burner side of the A-Coil. And from what my brother-in-law saw, it was pretty clean. I'll have to interrogate him a bit more. Here's a video of my furnace operating: http://www.youtube.com/watch?v=qX7gLpW5Gy0 . The A/C unit below it is not shown.
Here is a picture of the A-Coil http://www.flickr.com/photos/52730583@N02/5245096061/ It looks pretty clean. I know it doesn't show it through the fins, but it looked pretty clean too. Here's the cam view http://www.flickr.com/photos/52730583@N02/5245710436/
I'm stumped. The furnace is still acting up albeit slightly better.
Last night at about 6:30, the furnace was in lockout mode, this time with a 3 blink error code which indicates pressure switch problems. I shut the furnace down. Lowered the thermostat to the lowest temp, turned the furnace on, then jacked the thermostat up to 68. It was 63 in the house at the time. Since then, the furnace has run normally. Why was I not getting pressure switch errors before? Not sure. The spider's webbing inside the tubing created a partial seal on the low pressure switch. The strange thing is, before the spider and the spider's web was cleared out of the tubing and the valve, I verified that the pressure switch was working. I could actually see the pressure switch being activated. Otherwise the furnace wouldn't have worked. And besides that, the first tech to look at it shorted the switch, to simulate normal closed, and still the furnace would shut of after a few minutes.
I just hope the furnace lasts through the winter.
Thanks for the help Phil.
Woke up this morning to 60 degrees downstairs. It was considerably colder upstairs. Couldn't get the furnace to stay on more than a few minutes. I unplugged and replugged the connections to the transformer, something which I have done several times previously, and now it's been working for about 3 hours, cycling correctly, and bringing the house up to 71, then coming back on at 69. We'll see how long this lasts. - Just got back from eating out. Furnace is totally dead. Will not start.
Opps. I had it in info only mode .. it in answer mode now, you can accept! Thanks, Phil
The furnace is fixed. Thanks to my brother Justin, and no thanks to 4 servicemen who all said I needed a new furnace. That's 4 different guys. Two companies, four guys. The incompetence out here in New Jersey is mind blowing. While it was a difficult problem to diagnose because of the furnace cutting out intermittently and inconsistently, it should not have been a problem for someone who works in the business and has years of experience. My brother isolated the problem to be the gas valve. With the gas valve removed, we ran the 24 volt transformer wires directly to the primary coil in the gas valve. Needless to say there was no flow, we could hear it try to actuate, it clicked when the wires were connected to the coil connector, but the valve didn't open. He bought a new valve and we installed it together with him doing most of the work. I will assume that the one time I did get an open thermal cutout switch was a false positive. It actually was not too cold in the house although the temp the last few nights was in the teens. I was really thrown for a loop when the last two guys to try to fix it said they put in a valve and it didn't work. I guess they wired it wrong. Oh well, problem solved.