York Furnance Blowing Cold - Flash 7

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Old 11-08-09, 12:34 PM
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Smile York Furnace Blowing Cold - Flash 7

6-year old York Diamond Deluxe 80
RTH7500D Thermostat

Noticed that it was blowing cold air. Checked, and main fan blowing, burner was off. Turned thermostat down/up, off/on. Had to turn power off to furnace to reset.

Worked fine for a week. Started again. Control module flashing 7.

Always works fine when I am looking. Turn thermostat up, small fan blows, igniter comes on, gas starts and ignites, strong flames, then more gas and main fan starts.

Checked flame sensor and cleaned with steel wool. No difference.

Maybe bad flame sensor?? I can check the dc output of the sensor. Any idea on range of sensor?

Other ideas???

Thanks Fraser Jim
 
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Old 11-08-09, 01:41 PM
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Originally Posted by fraser jim View Post
6-year old York Diamond Deluxe 80
RTH7500D Thermostat

Noticed that it was blowing cold air. Checked, and main fan blowing, burner was off. Turned thermostat down/up, off/on. Had to turn power off to furnace to reset.

Worked fine for a week. Started again. Control module flashing 7.

Always works fine when I am looking. Turn thermostat up, small fan blows, igniter comes on, gas starts and ignites, strong flames, then more gas and main fan starts.

Checked flame sensor and cleaned with steel wool. No difference.

Maybe bad flame sensor?? I can check the dc output of the sensor. Any idea on range of sensor?

Other ideas???

Thanks Fraser Jim

If its only running for a few seconds and cutting out most likely


Door should have code chart on it .

 
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Old 11-08-09, 02:35 PM
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It actually will heat up the house, so I think that it is initial running and cuts out after running for quite awhile or cutsout after trying to restart with a call from the thermostat.

No chart on the doors, but it is flashing code 7. From a York manual, this means "flame could not be established".

Everything looks good, when I have been watching. Ignitor glows everytime, gas flows, burner shoots out strong flame across flame sensor.

??
 
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Old 11-08-09, 03:08 PM
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You need to measure the DC Micro-amps flowing from the flame sensor as in Grims very helpful illustration.
Keep in mind that we are talking micro-amps ---- 1,000 uamps= 1 milliamp.

You need to check that measurement when the furnace burners are operating and the flame sensor is engulfed by the burner flame.

Another double check is to measure the AC volts on the flame sensor wire when the burners are on.
 
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Old 11-08-09, 03:28 PM
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Thanks guys,

No problem with the DC.

So should the AC measurment be between the lead on the flame sensor and ground?

Any idea what measurment is acceptable?

Does it sound like the flame sensor or other?

Fraser Jim
 
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Old 11-08-09, 03:57 PM
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What was the DC micro-amp read you got?

The AC voltages from the ignition control can vary from 24 or so to 120.



Seattle Pioneer
 
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Old 11-08-09, 04:14 PM
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I am not at the house now.

Might be tomorrow night before I get a chance to take DC.

I have a Fluke Scopemeter that I will use.

Anything else that I should look at?

Thanks for the help.

Fraser Jim
 
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Old 11-09-09, 04:00 AM
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Originally Posted by fraser jim View Post
It actually will heat up the house, so I think that it is initial running and cuts out after running for quite awhile or cutsout after trying to restart with a call from the thermostat.

No chart on the doors, but it is flashing code 7. From a York manual, this means "flame could not be established".

Everything looks good, when I have been watching. Ignitor glows everytime, gas flows, burner shoots out strong flame across flame sensor.

??

Flame sensors are usually bad or good from my exp.
You need to sit down with a few cold onez and wath seq. of events.

inducer motor cones on (sounds like you got a two speed , which will have 3 or 4 going 2 it).
pressure switch closes (you may have 2) , (1 may be sticking)
ignitor lites
gas flows
2nd stage kicks in gas flows more
Inducer moter goes 2 2nd speed

Watch this operation when you got time to spend doing so and let us know.
gas flows
 
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Old 11-09-09, 08:47 PM
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So, I got home and turned up the thermostat.

Heat turned on fine and I ran for about an hour before house came up to temperature.

Then the furnace cycled on for about five minutes and then off for about five minutes for a number of times.

i turnd the thermostat down and let sit for about five minutes. Then I turned thermostat up and watched:

-The inducer motor come on.

-The ignitor lights.

-Then nothing.

-The ignitor cycles off and then on again.

-I tap the gas valve. Nothing.

-I tap the pressure switch and the gas comes on and fires.

Everything runs fine. Continues to run fine.

So I am presuming that the pressure switch is sticking??

What is pressure switch sensing and should I check first??

Is the pressure switch servicable? or do I swap it for a new on? or could it be one of the microswitchs on the pressure switch? or other??

Thanks,

FJ
 
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Old 11-09-09, 11:01 PM
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Are there diagnostic codes indicating that the pressure switch is opening? I'm supposing not or you would have mentioned them.

Tapping on the pressure switch isn't an adequate test that it's failing to close properly. Use an AC voltmeter to see if it's opening and shutting off the burners.

There's only a 5% chance that the pressure switch is bad. Usually the pressure switch opens because the venting system or the furnace itself is plugged up in some way and not operating properly.
 
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Old 11-10-09, 03:27 AM
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Originally Posted by SeattlePioneer View Post
Are there diagnostic codes indicating that the pressure switch is opening? I'm supposing not or you would have mentioned them.

Tapping on the pressure switch isn't an adequate test that it's failing to close properly. Use an AC voltmeter to see if it's opening and shutting off the burners.

There's only a 5% chance that the pressure switch is bad. Usually the pressure switch opens because the venting system or the furnace itself is plugged up in some way and not operating properly.

Pull the hose and stick a toothpick in it carefull not to break it off (could be stopped up ) pressure switch diaphragm could be weak , or switch on it could be bad , or not enough pressure due to blockage , or wheel slipage (if plastic housing) , or a few blades off wheel if metal housing......


Also if inducer is running , then it goes all the way to ignitor lites check for 24+- volts at gas valve.............
 
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Old 11-10-09, 07:33 AM
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Well, it did it again this monring, but I wasn't there to observe.

Some more info. on pressure switch.

It has a loop of hose with both ends on switch. There is a tee in the middle of the hose and a hose off of the tee that goes over to the inducer motor. Markings is .35" WC PF.

Also, has two sets of leads going to switch. I am presuming that I could temporarily jumper the two sets of leads and see if the problem occurs again.

Can I pull the hose off of the inducer and see what kind of vacuum it pulls with my old car vacuum gauge?

The vent from the furnace and the vent from the gas hot water heater go into a common vent pipe. My gut says that the problem occurs when the hot water heater is running, but I'm not sure.

I think the common vent goes to the chimney.

Will check the inducer.



FJ
 
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Old 11-10-09, 08:53 AM
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Unfortunately, you aren't really being helpful in following a reasonable diagnostic method. You keep going off in whatever directions that suit your guesses, without checking much of anything in enough detail to identify or eliminate it as a problem.

At the beginning of the thread you said you were getting a diagnostic code for a flame failure. You were asked to check the microamps ---- no report on the result of that.


Were you getting a diagnostic code after the HSI warmed up but the burners failed to light? That could be causing a flame failure diagnostic code as well.
 
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Old 11-10-09, 09:08 AM
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Originally Posted by fraser jim View Post
Well, it did it again this monring, but I wasn't there to observe.

Some more info. on pressure switch.

It has a loop of hose with both ends on switch. There is a tee in the middle of the hose and a hose off of the tee that goes over to the inducer motor. Markings is .35" WC PF.

Also, has two sets of leads going to switch. I am presuming that I could temporarily jumper the two sets of leads and see if the problem occurs again.

Can I pull the hose off of the inducer and see what kind of vacuum it pulls with my old car vacuum gauge?

The vent from the furnace and the vent from the gas hot water heater go into a common vent pipe. My gut says that the problem occurs when the hot water heater is running, but I'm not sure.

I think the common vent goes to the chimney.

Will check the inducer.



FJ

Also, has two sets of leads going to switch. I am presuming that I could temporarily jumper the two sets of leads and see if the problem occurs again.
> NO THAT IS A SAFETY <
If you start doing this you can damage u to the circuit board or transformer , but if you are lucky just blow a fuse !! + if done before furnace cycles , it will show a closed circuit code.

-----------------------------------------------------------


It has a loop of hose with both ends on switch. There is a tee in the middle of the hose and a hose off of the tee that goes over to the inducer motor. Markings is .35" WC PF.

If you have one that reads water column then yes.

-----------------------------------------------------------
 
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Old 11-10-09, 10:48 AM
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SeattlePioneer is right.

So far, I have only had limited time to be in front of the furnace because of my work.

I have been thinking that since the problem is very intermittent,
the measuremets would not be very useful until I could get consistent failures.

I will try tonight and report back.

FJ
 
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Old 11-10-09, 11:06 AM
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Originally Posted by fraser jim View Post
SeattlePioneer is right.

So far, I have only had limited time to be in front of the furnace because of my work.

I have been thinking that since the problem is very intermittent,
the measuremets would not be very useful until I could get consistent failures.

I will try tonight and report back.

FJ

I think with time we can narrow this down.
 
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Old 11-10-09, 11:14 AM
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Intermittent problems often imply marginal parts or conditions.

Take a furnace shutting off on a failure to detect flame rectification. The normal microamps may be 5-6, and the furnace may shut off a 1 microamps. Suppose you measure and get a read of 1.2 microamps --- that might lead you to check for why the reads are so marginal rather than a robust 5-6 that is likely to produce reliable operation.

Similar things happen with a pressure switch, among other things.

Intermittent problems often are the bane of repairmen, ---and are worse for DIYers, because they often require the greatest skill to track down.

Of course, it's very common for intermittent problems to become chronic problems and then outright failures over time. So eventually they can often become a lot easier to identify!

(I had a gold crown come loose, and put it back on the tooth without paying much attention to which tooth it was, figuring that the dentist would be able to figure that out easy enough.

Not true. The dentist told me he could pry any crown off if he wanted, but none were loose or were easy to get off. So he couldn't identify which was the problem to properly reinstall it.


Two years later after chronic tooth ache and the need for a root canal, the problem tooth finally revealed itself!)
 
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Old 11-10-09, 05:29 PM
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Originally Posted by fraser jim View Post
Well, it did it again this monring, but I wasn't there to observe.

Some more info. on pressure switch.

It has a loop of hose with both ends on switch. There is a tee in the middle of the hose and a hose off of the tee that goes over to the inducer motor. Markings is .35" WC PF.

Also, has two sets of leads going to switch. I am presuming that I could temporarily jumper the two sets of leads and see if the problem occurs again.

Can I pull the hose off of the inducer and see what kind of vacuum it pulls with my old car vacuum gauge?

The vent from the furnace and the vent from the gas hot water heater go into a common vent pipe. My gut says that the problem occurs when the hot water heater is running, but I'm not sure.

I think the common vent goes to the chimney.

Will check the inducer.



FJ
Car vacuum gauges measure in Hg (inches mercury). And to pull an inch of mercury requires way more vacuum than pulling an inch of water....let alone a fraction of an inch of water. Your Hg car gauge would not even quiver off 0.

So you have some sort of 4-wire 2 vacuum tube pressure switch? Identify abbreviations at each terminal to see what is NO, NC, and C. Besides direct jumping, you should be able to test from the correct terminal to see if power is passing thru and/or sustained.

In the case of a shared vent system, the main chimney would be like the trunk line, and the WH and furnace would be branch lines, each smaller than the trunk.... with the WH being the smallest. If set up by a contractor, chances are this set-up is not the issue unless you had a chimney blockage.
 
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Old 11-11-09, 09:14 AM
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Thanks for all of the input.

Latest update.

The furnace did not fail last night or this morning.

Last night I:

1. Tried to get microamp. readings on flame sensor. Meters were not sensitive enough. Hooked up a Fluke Scopemeter and reads 17.9 volts AC with burner on. When burner was off, reads 19.8 volts. Voltage drop as resistance rises? Set this to recored mode and it was consistent as burner cycled on and off.

2. Hooked up a 3-phase electrical logging power recorder as follows.

Channel #1 - to First Stage Pressure Switch Output. This reads 25+ volts AC 3 seconds after inducer motor turns on.

Channel #2 - to First Stage Gas Valve. This reads 25+ volts AC 17 seconds after inducer motor turns on.

Channel #3 - to Second Stage Pressure Switch Output. This reads 25+ and cycles on and off.

3. Poked with toothpick.

4. Watched seq. of event as outlined by Grim. Everything ok.

5. Took some pictures of wiring diagram and furnace guts. Can't figure out how to attach.

Furnace vent duct is about 4" dia. and then goes into an "expander?" which is about 6". Water Heater duct may be 3". It goes into side of expander. Looks like it expands again and then looks like it pipes over to chimeny (shared with fireplace?)

Thinking of moving Channel #3 lead to flame sensor.

Will send my wife up on the roof and let her scope out chimney.

I have more power recorders. Any thoughts on where to attach them?

FJ
 
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Old 11-11-09, 11:08 AM
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Great. You have everything except the test equipment you actually need to identify the problem.

And like most DIYers you go gallivanting off in odd directions rather than pursue a purposeful diagnostic procedure.

The first reply you got recommended checking the flame rectification current, and even posted a helpful diagram on how to do that. Still not done, and still one of the two key tests that need to be done to identify the problem, the other being to correctly measure the pressure being applied to the pressure switch.

Oh, well.
 
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Old 11-11-09, 11:21 AM
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So - I am learning as I go.

Do you have a recommendation for a meter that measures microamps.?

Never saw anything on how to measure the pressure being applied to the pressure switch. Recommendations for that?

FJ
 
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Old 11-11-09, 04:36 PM
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But if the furnace works correctly while you try to test, the test will show everything is good. All you can do is routine maintenance on everything (like see if external venting (exhaust and/or intake, if applicable)is good, no condensate is backed up, all electrical connections are good, that if you have an HSI...that it has the proper resistance) - and hope one of them is it. Or wait for failure and then test. And then if it works from tapping, immediately turn down stat, then reset stat to call for heat again, and see if it works again without tapping. And do this procedure again, and maybe again. You have to always be aware of coincidences. Have the mindset that something is out to trick you.
 
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Old 11-11-09, 07:12 PM
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Actually, measuring the pressure being applied to a pressure switch can tell you a lot even if the problem is only intermittent.

If the pressure is right near the level that would cause the pressure switch to open, you know something is plugged up. You can start checking the venting, inducer motor, and heat exchanger for problems --- and when you find a problem you will be rewarded by the pressure reading bounding up to a normal level.

Alternatively, if the pressure is where it should be and the pressure switch is dropping out, it implies a problem with the pressure switch, tubing or something else.

That's why MEASURING THE PRESSURE WITH A MANOMETER is the practice of a good repairman when confronted by the possibility of a pressure switch opening.

It allows you to identify a problem rather than make guesses. And it usually allows you to fix even intermittent problems the first time out.

And frankly, people should measure the pressure even on equipment that's working fine. That allows you to measure the pressure easily, accurately and quickly after a while, and you get a chance to see the normal pressure various furnaces exhibit.

If people are smart, that use a notebook to record those pressures on equipment that's working OK so they would have a record to refer to when they have equipment that may NOT be OK.

GUESSING about pressure switches is SO COMMON, and SUCH a waste of time! Just measure it, for Pete's sake!
 
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Old 11-12-09, 04:15 PM
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Thanks for the latest tips.

Sounds like I need to get my hands on a manometer!

I will also start spelunking for restriction.

ecman51 - Where would you expect to see "the condensate backed up"?

I don't see any external drains from the furnace, or close by ducting, except for the air conditioning section that sits on top of the furnace?

I expect that when you are talking about

FJ
 
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Old 11-12-09, 05:51 PM
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Without rereading this whole thread.....maybe you don't even have a high efficiency condensing furnace, if you do not see condensate drain tubes except for those for the AC.
 
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