unhappy furnace

[rayzur9]

We have a Consolidated Industries model MBA080NH4R furnace, natural gas, with hot surface ignitor. Control board is a honeywell 406650.

Ever since we had our air conditioner (outside and attic split system) replaced, which came with new thermostat (basic digital readout type, though not programmable), our heater has exhibited some issues.

Say the house was 63F. we turn on the heat and set it to 69F. The fan in the furnace will kick on, the HSI glows, the flames ignite, nice centered blue flames, I see the flame sensor glowing, and warm air is blowing out of the vents in the rooms like it should be, but just as the wall thermostat reaches around 67F, I notice the air is no longer warm coming from the vents. Upon checking the furnace, I see the fan is still on, but the flames are not. The diagnostic light flashes dim/bright as is noted to be normal operation per diagnostic code table.

The furnace brought the house up to 69F at one point later on in the night, satisfying the tstat setting, but when the house dropped back down to 67F, and the furnace began its startup sequence, it sometimes lights and blows warm air for a few minutes, then the flames go off, and the fan stays on(set to auto). I at one point saw the HSI start to glow, then go out. So I just shut it off for a couple of hours.

If we turn it back on, it rarely but usually does not ignite with flames, but just blows ambient air. At times I have been able to turn the power off in the attic switch and turn it back on to "reset" it, but that doesnt seem to do anything anymore. Even though the diagnostic light glows bright/dim at all times, throughout all this, it still acts like what the manual says occurs with a burner limit circuit open. I just dont get how it can work nicely for thirty minutes at one time, satisfy the tstat, but then not be able to come back on .

[rayzur9]

just wanted to say I'm in Houston Tx. Most if not ALL of the hvac service companies here farm out their jobs to "less than communicable" contractors or "whoevers available in the area". I might as well go stand out on the street and drop trou.

[Marc]

You seem to indicate that the furnace works properly for only the first 30 minutes after applying power after which the burner fails. Another 30 minutes of operation is sometimes, but usually not possible by interrupting the power to the unit.

I would allow the furnace to function until the burner fails then check for proper voltages at each of the control card terminals. That might point you in the direction of the fault. If the voltages are all normal, I might suspect the main burner solenoid valve. I assume there is no problem with the gas supply or air in the gas line.

Marc

[Terence McCann]

Say the house was 63F. we turn on the heat and set it to 69F. The fan in the furnace will kick on, the HSI glows, the flames ignite, nice centered blue flames,

Which fan, the main blower that delivers air to the home or the little fan that is in the burner compartment above the burners?

If the main blower starts as soon as the t/stat calls for heat something is not wired correctly. Sounds like there is an unintentional feedback energizing the main blower through the control circuit. This could also be producing unpredictable conditions as you're seeing.

Perhaps when they installed the a/c they boffed the control circuit wiring some how.

[Jim Katen]

The first part of your problem sounds like a classic mis-adjusted anticipator. (Back in the day, there was a coil of wire in the mechanical thermostat that generated a small amount of heat and caused the 'stat to shut down the furnace before the ambient air hit the goal temperature. That way the system could "coast" for the last degree or two.) Modern electronic stats don't have mechanical anticipators anymore, but they do have an electronic version that might be adjustable via the programming controls.

Also, modern thermostats have different broad global settings depending on what kind of system they're installed on. Your stat might think that it's connected to an electric furnace, for instance, and is sending signals that would only make sense to an electric furnace. These settings, on some stats, are controlled by screws on the back of the stat.

I'll bet that your thermostat is somehow mis-adjusted or mis-programmed. Check the manual and check the global settings.

- Jim Katen, Oregon

[rayzur9]

Thanks very much for the ideas. JK, the stat has a small switch for elec/gas. It is placed on the gas setting. Also, the anticipator is digital, and changed by pressing the arrow keys on the keypad. It currently is set at factory setting of no anticipation fore or aft.

Terrence, the fan i was referring to was the draft inducer motor which starts normally, , then ignition occurs, then the circulating fan comes on.

I watched the furnace last night, and after it brought the house up to stat temp setting, it turned off, household temperature got lower, stat called for heat, draft inducer started, HSI glowed for about half a second and it clicked off. No fans, nothing. Shut everything down. waited 2 hours, turned it all back on, turned on the heat, the furnace worked for 20 minutes warming the house about 3 degrees, but not to stat setting, and the furnace shut off. One thing though, the circulating fan no longer runs forever until I shut it off. It seems to run its normal 2 to 3 minutes as if the furnace has satisfied the stat temp setting. Before, the flames would go out and the fan would run until we shut it off. Now, its running its normal 2 to 3 minutes to cool combustion chamber and shutting off which seems its normal operation, except the furnace has not heated the house up to set temp on stat.

Looking at throwing parts at it. Planning on starting with the Q3400A HSI/Sensor assembly.

[hausdok]

Why don't you start by calling the manufacturer's technical assistance folks? They've probably encountered the problem on others' units and will know what the fix is.

ONE TEAM - ONE FIGHT!!!

Mike

[Jim Katen]

Thanks very much for the ideas. JK, the stat has a small switch for elec/gas. It is placed on the gas setting. Also, the anticipator is digital, and changed by pressing the arrow keys on the keypad. It currently is set at factory setting of no anticipation fore or aft.

Terrence, the fan i was referring to was the draft inducer motor which starts normally, , then ignition occurs, then the circulating fan comes on.

I watched the furnace last night, and after it brought the house up to stat temp setting, it turned off, household temperature got lower, stat called for heat, draft inducer started, HSI glowed for about half a second and it clicked off. No fans, nothing. Shut everything down. waited 2 hours, turned it all back on, turned on the heat, the furnace worked for 20 minutes warming the house about 3 degrees, but not to stat setting, and the furnace shut off. One thing though, the circulating fan no longer runs forever until I shut it off. It seems to run its normal 2 to 3 minutes as if the furnace has satisfied the stat temp setting. Before, the flames would go out and the fan would run until we shut it off. Now, its running its normal 2 to 3 minutes to cool combustion chamber and shutting off which seems its normal operation, except the furnace has not heated the house up to set temp on stat.

Looking at throwing parts at it. Planning on starting with the Q3400A HSI/Sensor assembly.

I'm still thinking the problem is related to the stat. It's the only thing that's changed. See if you can find an old Honeywell T87 stat (the round ones with the mercury bulb). Hook that up in place of your new fancy schmancy one. That'll tell you if you have a furnace problem or a thermostat problem.

- Jim Katen, Oregon

[rayzur9]

"ARS Service Express" when installing the new carrier a/c installed the White Rodgers thermostat.

Hausdok, Consolidated Industries filed for Chapter 11 and was sued in a class action lawsuit where they had to pay for partial replacement of furnaces purchased prior to 2001. The last date for filing a claim with that class action was back in April I believe. They pretty much dont have a "technical assistance" department anymore.

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[rayzur9]

After much scouring of the internet, I am finding that many of the components, such as the timer control module above, as well as the SmartValve gas valve, heat exchanger, and just about every other part in this furnace I have has been a nightmare for people all over the states. Lucky me. Luckily, Honeywell has many replacement parts. I will attempt a factory reset of the thermostat tonite, and see if that does any good.

[rayzur9]

The first part of your problem sounds like a classic mis-adjusted anticipator. (Back in the day, there was a coil of wire in the mechanical thermostat that generated a small amount of heat and caused the 'stat to shut down the furnace before the ambient air hit the goal temperature. That way the system could "coast" for the last degree or two.) Modern electronic stats don't have mechanical anticipators anymore, but they do have an electronic version that might be adjustable via the programming controls.

Also, modern thermostats have different broad global settings depending on what kind of system they're installed on. Your stat might think that it's connected to an electric furnace, for instance, and is sending signals that would only make sense to an electric furnace. These settings, on some stats, are controlled by screws on the back of the stat.

I'll bet that your thermostat is somehow mis-adjusted or mis-programmed. Check the manual and check the global settings.

- Jim Katen, Oregon

You know, they DID add some sort of level switch in the drain pan of the A/C condensor that had to be tapped into the supply coming out of the furnace. Big 12 ga wire nutted to little 18ga. wires...

[Marc]

That picture of the thermostat (47.85KB): where's the common wire? Electronic thermostats need the common (neutral) for proper operation.

[Terence McCann]

You sound pretty capable of working on it.

Before you buy any parts try jumping out the various limit controls, one at a time, for process of elimination. If the induced draft motor starts and then the hsi starts to glow and then everything shut down it sounds like the differential pressure switch that proves induced draft motor operation - this can be jumped out as well.

If the flame rod is crapping out the burners will light for 30 seconds or so and then shut down.

Good luck!

BTW, don't forget to remove the jumpers [:-magnify

[rayzur9]

That picture of the thermostat (47.85KB): where's the common wire? Electronic thermostats need the common (neutral) for proper operation.

Ive got 5 wires. Blue is not used, white wired to W, red wired to RC, Red jumper from RC to RH. Green to G, yellow to Y. It looks like it was wired per schema below.

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[Terence McCann]

That picture of the thermostat (47.85KB): where's the common wire? Electronic thermostats need the common (neutral) for proper operation.

No they don't.

The old ones perhaps but that goes way way back - perhaps as far back as the Honeywell Cronotherm?? I put a White Rogers in one of my homes back in 1991 that didn't need a common.

All you should need is a Red, Green, White & Yellow for proper operation (5th wire if you have a heat pump).

[rayzur9]

You guys have been a big help in the past for me, and again I really appreciate your input and expertise.

had the unit off all day and getting home from work it was 65 in the house, comfortable enough, but I turned the heat on at the stat and it was set at 69. It went thru proper startup sequence, ran fine and blew , warm for about 15 to 20 mins. top temperature reached was 66F.

about right for the space between furnace and stat therm.

then it shut off. no blower fan, normal diag light bright/dim.

I noticed the wiring diag above shows that batteries replaced properly make the neutral unnecessary.

The timer control module is mounted to a panel inside the funace that looks removable, (3 screws, foam gasket around). Is this an entryway to the air chamber directly before the exchanger, or actually into the exchanger itself?

[Jim Katen]

You guys have been a big help in the past for me, and again I really appreciate your input and expertise.

had the unit off all day and getting home from work it was 65 in the house, comfortable enough, but I turned the heat on at the stat and it was set at 69. It went thru proper startup sequence, ran fine and blew , warm for about 15 to 20 mins. top temperature reached was 66F.

about right for the space between furnace and stat therm.

then it shut off. no blower fan, normal diag light bright/dim.

I noticed the wiring diag above shows that batteries replaced properly make the neutral unnecessary.

The timer control module is mounted to a panel inside the funace that looks removable, (3 screws, foam gasket around). Is this an entryway to the air chamber directly before the exchanger, or actually into the exchanger itself?

At your own risk:

Disconnect the stat and put a jumper across the R & W terminals. What does the furnace do and for how long does it do it?

- Jim Katen, Oregon

[hausdok]

Is it equipped with one of those self-diagnostic setups with the LED that flashes code at you to tell you what's wrong with it?

OT - OF!!!

M.

[Jim Katen]

Is it equipped with one of those self-diagnostic setups with the LED that flashes code at you to tell you what's wrong with it?

Get with it, O'Handley! In his first post and his most recent post, he said that the diagnostic light indicated normal operation.

[rayzur9]

I just wanted to follow up on this issue with the furnace.

At first, I replaced the thermostat on the wall. This didnt help the furnace, or make a change in the operation of it.

I crawled up in the attic again, and had my wife turn on the furnace so I could listen and watch the cycle once more, and noticed an audible noise from the timer controller. An old Honeywell ST9141A1002 controller. I went to HVAC Parts Outlet online and purchased a flame sensor/ignitor (35$) and the upgraded version of the controller board, which was part number ST9120U1011 for about 100 bucks.

This controller was an easy install barring 2 wire connections I had to change to 1/4" to fit the terminals on the controller, the diagnostic light on the new controller flashed dim/bright for normal operation, and I am extremely pleased to say it seems to have enabled the furnace to maintain set thermostat temperature. For 3 days now the furnace has come on to maintain house thermostat temperature, and cycles normally again. Yay! Thanks for all your help guys.

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[hausdok]

Is it equipped with one of those self-diagnostic setups with the LED that flashes code at you to tell you what's wrong with it?

Get with it, O'Handley! In his first post and his most recent post, he said that the diagnostic light indicated normal operation.

[:-propell

[Terence McCann]

I just wanted to follow up on this issue with the furnace.

At first, I replaced the thermostat on the wall. This didnt help the furnace, or make a change in the operation of it.

I crawled up in the attic again, and had my wife turn on the furnace so I could listen and watch the cycle once more, and noticed an audible noise from the timer controller. An old Honeywell ST9141A1002 controller. I went to HVAC Parts Outlet online and purchased a flame sensor/ignitor (35$) and the upgraded version of the controller board, which was part number ST9120U1011 for about 100 bucks.

This controller was an easy install barring 2 wire connections I had to change to 1/4" to fit the terminals on the controller, the diagnostic light on the new controller flashed dim/bright for normal operation, and I am extremely pleased to say it seems to have enabled the furnace to maintain set thermostat temperature. For 3 days now the furnace has come on to maintain house thermostat temperature, and cycles normally again. Yay! Thanks for all your help guys.

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Good job! A furnace that is blowing warm air in January is always a good thing.

[jimmy1one]

I just read this thread what a mess but it is close to my issue. Again a Consolidated furnace I changed the gas valve and the igniter coil, one had a short and the other was burned out. The unit worked for 3 days now I has intermittent operation. Bottom line is no trial for ignition meaning the coil does not ignite the pilot or glow, fan running constantly. I'm thinking it's my turn to freeze a few days Until I can get the new fan control, can anyone offer any further insight? I know I'm late to the party but to be honest the furnace has worked well for 10 years I had no idea there a problem with Consolidated furnaces. There were multiple issues, once I got involved I have to have a working furnace. My thinking at this point is to solve the problem the OEM is not something I can deal with. Should I change the pressure switch also any help would be greatly appreciated.