Heater shuts off

cannelg

Hi all,

Looking for some help and another forum suggested here.  Have a Bryant furnace 313a that shuts off and shows code 33.  Had an ac company come out in December and they diagnosed a bad control board and blower motor.  Replaced both.  It’s rarely cold down here in Florida so heat isn’t used much, but it got cold last week.  Same problem is occurring.  Had them back out.  They think the issue is the duct sizes are wrong for the equipment.  House was built with a 3.5 ton unit.  2600 sq ft.  We upgraded to a 5 ton about 8 years ago.  This is the first I’ve noticed an issue though. I tested the limit switch and it seems to work.  Switched it out and the new one does the same.that limit switch opens when the unit gets too hot.  I tested resistance on all other switches and they seem fine.  Company did the same so I believe the switches are ok. The exhaust doesn’t seem to be blocked. If I open the bottom of the furnace where the air gets sucked in and tape the switch so it thinks the door is closed, (see pic), then the unit will stay on. I’ve also tried taking out both filters, and I cut a hole in the supply plenum to get more air in and it will still shut down.  The only way it will stay on is if I open that bottom door and tape the door switch to keep it on.  Ac company wants to take out all the ducts and replace with bigger.  Before I go with that huge expense, could I just add a return?  Or are there other ideas? 

EBEBRATT-Ed

Have you not run the heat in the last 8 years?

Nobody install larger ductwork than necessary.

Whoever jumped the size from 3.5 tons to 5 tons screwed you up you probably about 600 cfm short ductwork wise

Running without the blower door on will screw up your combustion air and and may overload the blower motor.

You can't just add a return you have to add supplies as well.

Must be a big house to need 5 tons How many square feet are you cooling?

cannelg

Thanks for the help.  About 2600 sq ft. I’m fine with adding supplies and returns.  I just don’t want to rip out everything that is there and replace - I’d rather add returns and supplies.  It’s a lot of money when the heat runs so little down here.  But Why is it just happening now? It’s all so weird.

  I’m sure the company that did it was eager to just put in the biggest unit they could. 

So barring anything else mechanical in there:


1. Does adding more duct work - return and supply - accomplish the same thing as replacing the ducts that are there with bigger ones?

2.  Does it sound reasonable that this is the issue and is there a way to prove it?  

Thanks,

Jamie Hall

Seems like things are pretty clear -- inadequate return air for sure, and possibly inadequate supply duct size. What that does is reduce the air flow, and -- inevitably -- causes the furnace to overheat. Whether you add new return ducts (and some supplies) or rip out ductwork and go bigger -- or a combination -- is really much more of an architectural problem. Which is going to be easier to do? And, perhaps more important, are there areas in the house which don't heat or cool as well as you might like? This might be an excellent chance to correct some of those problems.

I'd look at return ductwork first. It's almost always undersized, for some reason.

EBEBRATT-Ed

@cannelg

Yes there is a way to check if your moving enough air. You get the furnace running and let the temps stabilized. Then you check the furnace supply and return temps and subtract the return temp from the supply

That's your temperature rise. If you look on the furnace nameplate they will state what the temperature rise should be. Usually around 60 degrees or so. If it's low your moving to much air if its high your moving too little.

Did this just start happening suddenly?

I would have someone check the blower motor rotation and amp draw

Also could some of the supply or return ducts be blocked somewhere?

Did they check the gas input to be sure the furnace is not overfired?

Did a plastic bag get sucked into the blower wheel when the door was off?

Is the AC coil plugged up?

Filters clean?

Is this a 60,000 btu furnace?

cannelg

I believe the furnace is 110,000 BYU input and 90,000 btu output. (that's what the sticker says)

I only noticed when the power was going out at the thermostat. It's rarely cold enough down here to use heat but I haven't noticed issues in past years. They they diagnosed a bad control board and blower motor in December. Replaced those. Then we didn't need heat again until last weekend, and it started shutting off again.

Not sure if it will run long enough to get a stable temperature. It only runs for a few minutes. Probably less than 2-3, and then the limit switch turns it off. Tech checked all the components and said they are fine.

Had the roof done last year - I wonder if there is an issue I can't see. I can't get the vent cap off - I suppose that could be an issue - but I briefly tested the unit without the flue pipe on. (briefly) - but - it still shut off after about a minute of running.

I've look at all the supplies and none are blocked.

I have no idea about the gas overfiring. I wasn't here on the second visit when he came out to check things but I don't know if he checked that. Still, it's a little wierd that it just started happening. That being said, they put a new meter on this past year, but???

I crawled through the entire attic and wrote down the duct sizes that I could see. All are round flex ducts.

Main supply plenum feeds 3 distribution boxes...through three ducts:

Duct 1 - Size 10 round flex duct to distribution box. Box has4 other ducts attached: sizes 8,4,5 and 6.

Duct 2 - Size 12 round flex duct to distribution box. Box has 7 ducts attached, sizes 5,4,7,7,5,4,6

Duct 3 - size 12 round flex duc to other side of house distribution box. Box has 7 ducts attached: sizes 7,7,4,5,4,8,4

There are 2 returns:

18 x 30 grill with an 18" flex duct and an 18x18 grill with a 12" flex duct.

All ducts seemed fine. Nothing crushed or anything. House is about 2600 sq ft

Blower wheel spins. It seems fine. Troubleshooting that code says to check the capacitor. I don't see one....

I may just have another company come look. My neighbor has the exact same house built at the same time. He upgraded his unit and is not having issue. I may have to have another company come take a look. I dunno. Thanks.

wmgeorge

Ha ha if its been running fine for 8 years and one day the ducts were the wrong size! Bet a lot of money the A coil is packed full of dirt and crud, or B the the gas pressure is set too high on the valve, its over fired. You need to put the duct work back the way it was and check the AC coil first and then the gas pressure.

Find someone who know what the 7ell they are doing!!

PS the folks down South Love that flex, requires little or no skill to install and but restricts the air flow so much, but they don't know any better. I guess I have never seen flex dryer vent used on for furnace venting either.

Jon_blaney

I am a firm believer in looking at what has changed in a system. It runs fine, change, problem. Look at the change, the gas meter. Gas pressure is where I would look. It could be the furnace was firing at a lower pressure and is now oversized with the current pressure. I think the tech should have checked the pressure at the gas valve and adjusted it if necessary. Why was the meter changed. May need new gas valve.

cannelg

Gas company came by and changed it one day when we were out.  Not sure why.  Only other thing I can think of is that I gutted the bathroom that is right next to large return - had to grind down a lot of concrete between moving the drain and smoothing out the slab for new tile and that dust gets everywhere.  It’s possible that some - or too much - of that concrete dust made it under the door or out of the room and up to the return and into the system. That return is is about a foot from the bathroom in  the ceiling - 10 ft high. I can always take a look at that when I get home.  But I don’t know how to check gas pressure.  Might be better to call the original company who put the AC in and have them come to look.  I assume that just closing the gas valve a little to test the theory wouldn’t work? Id stil call them out to make sure it is adjusted properly, but just as a test, if I close the valve a little for less of a flow to see what happens, could that test it?

Jon_blaney

Don't mess with the gas valve. This work is not DIY. You need measuring equipment.

wmgeorge

I guess I missed the part where the gas meter was changed?

had to grind down a lot of concrete between moving the drain and smoothing out the slab

Construction dust, AC coil = plugged coil. Simple. Check first.

Overfired, check gas pressure for the ? service tech, does he know how??

Returns undersized> Put in some real sheetmetal the correct size.

pecmsg

cannelg said:

Gas company came by and changed it one day when we were out.  Not sure why.  Only other thing I can think of is that I gutted the bathroom that is right next to large return - had to grind down a lot of concrete between moving the drain and smoothing out the slab for new tile and that dust gets everywhere.  It’s possible that some - or too much - of that concrete dust made it under the door or out of the room and up to the return and into the system. That return is is about a foot from the bathroom in  the ceiling - 10 ft high. I can always take a look at that when I get home.  But I don’t know how to check gas pressure.  Might be better to call the original company who put the AC in and have them come to look.  I assume that just closing the gas valve a little to test the theory wouldn’t work? Id stil call them out to make sure it is adjusted properly, but just as a test, if I close the valve a little for less of a flow to see what happens, could that test it?

Did the gas company measure inlet and outlet pressure? Was a combustion analyses performed after changing the valve?

That unit should have been OFF during construction. You'll need someone to pull and clean the blower motor and squirrel cage fan and possibly the evaporator coil as well.

cannelg

I won’t mess with the gas - I’ll see about getting another company to look at that.

To clarify - the meter outside was changed but not the gas valve at the furnace.  They changed it And left a note.  I can’t remember anything else about it other than they left an note that it was changed and a number to call them with any issues.

I will check the coils when I get home as a start.  Then figure out who to call about the gas. They changed the blower motor in December.  

I’ll update you when I have more info.

thanks

Jon_blaney

Maybe check with the Gas company.

pecmsg

Must be a Isl of long thing. If the gas is shut for any reason PSE&G relights Everything! (and it better be up to code)

JUGHNE

Beside the dirt and dust being a problem, the gas pressure could have been turned down on the install years ago because of limit tripping.

Then the gas co may have raised/corrected the incoming pressure with meter change.

wmgeorge

pecmsg said:

Must be a Isl of long thing. If the gas is shut for any reason PSE&G relights Everything! (and it better be up to code)

Auto ignition on the new stuff and I am assuming the meter is on the outside no need to come in the house.

mattmia2

Here in michigan if they shut off your service for any reason they won't turn it back on until you are there to let them in to do a safety check.

cannelg

Jon_blaney said:

Maybe check with the Gas company.

Funny - I called them this morning.  They looked it up and said that changing the meter was just because the house was 20 years old and needed updating. They said it shouldn’t change the house pressure at all but they will send someone out Friday to check the outside pressure at least.  Maybe they will be nice and check the pressure at the furnace / I dunno.

Having already put $500 in to this furnace since December, I am trying to do as much as I can myself - partly because I really enjoy the troubleshooting and learning, partly because I don’t want to spend much more.  If I have to do the ducts I will, but I had one off her thought…

Is it possible that although the exhaust inducer motor is running ok, could it be not pushing the exhaust fumes out fast enough?  That flue gets awfully hot.  Is there a way to test it to know that it isn’t just running slower than it should?  

If I can rule out the coils, and the inducer motor, then the only thing left really is the gas pressure or ductwork.

mattmia2

You can to some extent verify the input by clocking the meter. If the pressure is off on the regulator at the meter then the meter won't read correctly.

Does it do the same thing if you jumper w and r at the furnace, are you sure the thermostat isn't having an issue?

Checking the coil might be a challenge. You might be able to see something from above shining a flashlight down between the fins or see it from below through the heat exchanger if you remove the blower. If the blower is all caked with dirt, especially masonry dust, that will reduce the output but hopefully they cleaned it when they replaced the motor. Did they replace the capacitor with the motor wherever it is?

cannelg

mattmia2 said:

You can to some extent verify the input by clocking the meter. If the pressure is off on the regulator at the meter then the meter won't read correctly. Does it do the same thing if you jumper w and r at the furnace, are you sure the thermostat isn't having an issue? Checking the coil might be a challenge. You might be able to see something from above shining a flashlight down between the fins or see it from below through the heat exchanger if you remove the blower. If the blower is all caked with dirt, especially masonry dust, that will reduce the output but hopefully they cleaned it when they replaced the motor. Did they replace the capacitor with the motor wherever it is?

I haven’t tried jumping w and r at the furnace - I was afraid to. Lol. If I put a small jumper between those, what does it do? I assume your talking about the pic below?  It’s a 2 stage ac but a 1 state compressor. I honestly don’t know if the thermostat is ok.  It gets confusing between humidity settings.  It’s a 2 stage A/C and a single stage furnace.  I supposed the thermostat could be calling for the wrong stage?  Or there is a setting on the board that could be wrong since it was replaced. So if I 

JUGHNE

When the blower motor was replaced it could have been connected to a lower speed than the original.

pecmsg

wmgeorge said:

Must be a Isl of long thing. If the gas is shut for any reason PSE&G relights Everything! (and it better be up to code)

Auto ignition on the new stuff and I am assuming the meter is on the outside no need to come in the house.

And how do they know that?  

Once gas service has been interrupted they Must check   

cannelg

pecmsg said:

wmgeorge said:

Must be a Isl of long thing. If the gas is shut for any reason PSE&G relights Everything! (and it better be up to code)

Auto ignition on the new stuff and I am assuming the meter is on the outside no need to come in the house.

And how do they know that?  

Once gas service has been interrupted they Must check   

Actually, you’re right . Now that I think about it, they replaced it and left a note but the gas was off.  We had to call and they came back out to turn it on and set the pilot light on the water heater.

But that got me thinking - our hot water is way hotter than it used to be.  I had to turn it to the lowest setting and it’s still pretty hot.  I didn’t make that connection before but now I am wondering if it really is the gas.  

pecmsg

@cannelg
concerning the HW. 
Your tank temperature needs to be at 140* to prevent legionnaires disease.   
then a mixing valve is needed reducing the temperature to less then 110 -120* for point of use. 

wmgeorge

pecmsg said:

wmgeorge said:

pecmsg said:

Must be a Isl of long thing. If the gas is shut for any reason PSE&G relights Everything! (and it better be up to code)

Auto ignition on the new stuff and I am assuming the meter is on the outside no need to come in the house.

And how do they know that?  

Once gas service has been interrupted they Must check   

Our power company both the gas side and electric calls us to make sure. After an outage of either service. No notes.

cannelg

Coil looks clean.  I don’t have a manometer to check the gas pressure. Doesn’t seem too difficult to do but hopefully the gas company guy will be willing to check. 

wmgeorge

cannelg said:

Coil looks clean.  I don’t have a manometer to check the gas pressure. Doesn’t seem too difficult to do but hopefully the gas company guy will be willing to check. 

Which side of the coil did you look at, was there an access panel? If the whole front panel comes off, there is another panel under that to see the inside air entering side. Leave the gas to someone who knows what they are doing. But if the coil is clean, it has to be over fired or a duct restricted issue, and flex can collapse.

cannelg

Ok yeah - I only saw the top but it was very clean.  I tried taking the lower panel off but couldn’t see anything.

Here is a 12 second clip of the exhaust blower before it shut down.  Does this sound normal?

https://youtu.be/HZvFKCrCbYU

If it’s not the gas or the coils or this - it’s gotta be the ducts I guess.  Or they hooked up the blower wrong but I don’t think that’s the case.  

mattmia2

can you show us a picture or 2 of the schematic inside the furnace? It should show us if the blower motor has a capacitor. If the blower has a bad cap and they didn't change the cap with the motor, the blower will develop less power and won't spin as fast. I had this issue with a condenser, i replaced the cap with the fan motor and the replacement cap was low quality and it failed in a couple years. The fan would run but not at full speed so the system capacity wasn't right.(there is a longer story involving charging it to run at that point after it has lost some refrigerant over 5 years or so through a very slow leak)

cannelg

mattmia2 said:

can you show us a picture or 2 of the schematic inside the furnace? It should show us if the blower motor has a capacitor. If the blower has a bad cap and they didn't change the cap with the motor, the blower will develop less power and won't spin as fast. I had this issue with a condenser, i replaced the cap with the fan motor and the replacement cap was low quality and it failed in a couple years. The fan would run but not at full speed so the system capacity wasn't right.(there is a longer story involving charging it to run at that point after it has lost some refrigerant over 5 years or so through a very slow leak)

Sure - here are some pics.

pecmsg

mattmia2 said:

can you show us a picture or 2 of the schematic inside the furnace? It should show us if the blower motor has a capacitor. If the blower has a bad cap and they didn't change the cap with the motor, the blower will develop less power and won't spin as fast. I had this issue with a condenser, i replaced the cap with the fan motor and the replacement cap was low quality and it failed in a couple years. The fan would run but not at full speed so the system capacity wasn't right.(there is a longer story involving charging it to run at that point after it has lost some refrigerant over 5 years or so through a very slow leak)

2014 date code it’s a ECM Motor. 

mattmia2

If there is a capacitor for the blower it is mounted on the motor itself or on the blower housing underneath or in back and isn't shown on the schematic.

cannelg

Yeah - so not the cap.  I really don’t think it is the coils.  If the draft inducer motor is working, the only thing left to check is the gas pressure.  If that is ok, then I guess it really is the duct work, but it’s just odd that it was fine for 8 years. 

wmgeorge

pecmsg said:

mattmia2 said:

can you show us a picture or 2 of the schematic inside the furnace? It should show us if the blower motor has a capacitor. If the blower has a bad cap and they didn't change the cap with the motor, the blower will develop less power and won't spin as fast. I had this issue with a condenser, i replaced the cap with the fan motor and the replacement cap was low quality and it failed in a couple years. The fan would run but not at full speed so the system capacity wasn't right.(there is a longer story involving charging it to run at that point after it has lost some refrigerant over 5 years or so through a very slow leak)

2014 date code it’s a ECM Motor. 

I think your on to something, since your a Carrier dealer and this is a Bryant on the parts look up they indicate a ECM motor on some models???? Not sure if this is screw up or they put the wrong motor and control board in? Someone in the Carrier / Bryant network needs to check this out and see what is true or not.

mattmia2

Is the blower turning the right way? I'm very suspicious of the original diagnosis of both the board and the motor. If you pull out the blower motor and look at the labels on there it will tell more of the story but getting there is a bit of a project.

Do you have the old motor?

cannelg

By the way - this is the limit switch that keeps shutting it down.  And that flue pipe is too hot to touch.  The one to the left of it stays closed and they aren’t that far from each other.  Any chance the draft inducer motor is the problem?  

cannelg

mattmia2 said:

Is the blower turning the right way? I'm very suspicious of the original diagnosis of both the board and the motor. If you pull out the blower motor and look at the labels on there it will tell more of the story but getting there is a bit of a project. Do you have the old motor?

No - I don’t have the old motor.  What would I be looking for?  I can pull out the new motor and take a look or a pic.

Curious  about something else…the thermostat is on one wall but then connects to this wiring block inside the furnace closet.  What is the orange wire in Rh and why isn’t the brown wire connected to anything?

it’s a two stage compressor.

cannelg

mattmia2 said:

Is the blower turning the right way? I'm very suspicious of the original diagnosis of both the board and the motor. If you pull out the blower motor and look at the labels on there it will tell more of the story but getting there is a bit of a project. Do you have the old motor?

Here is a pic of the motor label…

pecmsg

All units manufactured after 2010 have ECM motors!

JUGHNE

This shows an inductor coil for the 1 HP motor.
If it is defective could that be a problem?