Heater shuts off

delcrossv

Just throwing it out there, but I had a Bryant condensing furnace where the HX rotted and tripped the high limit (also at about 8 years). Don't know if that's also a problem with lower efficiency models.

mattmia2

the inductor is just a coil of wire. it is probably just for rfi suppression

mattmia2

take a look at the burner when the blower kicks on, does it change?

EBEBRATT-Ed

@cannelg

looking at your duct sizes you have 3 1/2 tons of cooling so you need ducts to move 400 cfm/to so 3.5 x 400=1400cfm. The heating cfm is always lees

your supplies to the distribution boxes are 1@10" & 2@12' the 10" will do 400 and the 2 12' will do 650 each so 650 +650+400=1700cfm so they are big enough

1 10" feeds 8,4,5 6 the 8 will do 200, the 4" 40. 5"60 6" 100 that adds up to 400cfm total so that is fine

1 12" does a 5,4,7,7.5.4.6 so thats 60 +40+150+150+60+40+100=600 so that is fine

1 12" does 7,7,4,5,4,8,4, thats150+150+40+60+40+200+40=680 so thats fine

The returns the 18 x 30 grill is good for 1400 cfm the 18" flex is good for that

the 18 x 18 grill is good for 900 cfm the 12 ' flex is good for 600

so 600 +1400=2000cfm

So happy news your ductwork if not restricted, blocked or disconnected id large enough. Make sure the registers are open and filters clean.

1. turn the thermostat to fan and run it with out the heat and see if all the supplies are blowing air and returns sucking air
2. Clock the gas meter or check the gas pressure at the burner. The burner manifold shouls be 3 1/2" wc for natural gas
3. Check the temp rise across the furnace.


Your service company is all wet your ductwork is size right if not blocked

wmgeorge

It was my understanding he upgraded to 5 ton AC. I have worked on a lot of ECM units, that motor is marked 1 Hp 120 volts unlike any ECM motor I have seen?
Duct sizes, this is all Flex and how long are the runs? I don't run flex, we were only allowed to run 6 feet if we did, the SM or Tinners did the ducts. Need someone there to actually look and measure.

cannelg

EBEBRATT-Ed said:

@cannelg looking at your duct sizes you have 3 1/2 tons of cooling so you need ducts to move 400 cfm/to so 3.5 x 400=1400cfm. The heating cfm is always lees your supplies to the distribution boxes are 1@10" & 2@12' the 10" will do 400 and the 2 12' will do 650 each so 650 +650+400=1700cfm so they are big enough 1 10" feeds 8,4,5 6 the 8 will do 200, the 4" 40. 5"60 6" 100 that adds up to 400cfm total so that is fine 1 12" does a 5,4,7,7.5.4.6 so thats 60 +40+150+150+60+40+100=600 so that is fine 1 12" does 7,7,4,5,4,8,4, thats150+150+40+60+40+200+40=680 so thats fine The returns the 18 x 30 grill is good for 1400 cfm the 18" flex is good for that the 18 x 18 grill is good for 900 cfm the 12 ' flex is good for 600 so 600 +1400=2000cfm So happy news your ductwork if not restricted, blocked or disconnected id large enough. Make sure the registers are open and filters clean. 1. turn the thermostat to fan and run it with out the heat and see if all the supplies are blowing air and returns sucking air 2. Clock the gas meter or check the gas pressure at the burner. The burner manifold shouls be 3 1/2" wc for natural gas 3. Check the temp rise across the furnace. Your service company is all wet your ductwork is size right if not blocked

Wow - thanks for doing all that math.  It’s a 5 ton unit.  Runs vary.  That last distribution box is across the house from the others but the first two are pretty close to the supply
plenum. But I didn’t measure how long each run was.  I could try to ballpark it or go back up and take measurements of the length of each run.  First I want to see what the gas guy says today. 

I found this is the furnace closet from the original install….does it mean anything?

cannelg

Gas company checked and gas is fine.  That’s not if.  The company that put the unit in 8 years ago is coming out for a second opinion.  We’ll see.

cannelg

Just updating in case anyone is curious - tech from the original company who installed the unit came to look.  Lowered the gas down to 1.8 and put the blower speed on high (swapped cooling and heating I think) and it ran longer but still eventually shut down. He put the gas back up but left the blower switched like that.  Checked the static pressure and it was .6.  Said that he thinks the unit is just older now and more airflow would help.  Thing is, in Florida we use the heat so infrequently that I am not sure it is worth the expense/ 


side note - he said that the thermostat shouldn’t be losing power when the heat shuts off.  That is what is happening.  He thinks the thermostat has an issue, but that is separate from the overheating .  But it begs the question / I wonder if I only noticed it now because of the thermostat going out and maybe it has been doing this all along?   Truthfully, it could have been turning on and off the whole time and I really wouldn’t have known.  It’s never cold enough during the day.  I only started noticing it because of the power to the thermostat being shut off.  

Anyway - that’s the update.  

Jamie Hall

Oh dear. A nice smart thermostat? And miswired so it only gets power under certain conditions. I think it has nothing at all to do with the furnace -- and everything to do with a miswired thermostat.

cannelg

Jamie Hall said:

Oh dear. A nice smart thermostat? And miswired so it only gets power under certain conditions. I think it has nothing at all to do with the furnace -- and everything to do with a miswired thermostat.

Not sur did it is miswired - or just bad.  Yeah said they stopped using them and I noticed they are discontinued.  I’m going to get a new one. Any advice?  Bryant 2 stage a/c , one stage furnace .

wmgeorge

Maybe its hard down there to find someone who knows the basics of troubleshooting and HVAC. For $2000 I can fly down, and I would bring a thermometer?
PS Its not the thermostat, and did anyone check the air entering side of the AC coil?

cannelg

Lol! I just summarized the check.  He didn’t say thermostat was the issue, even though it is wonky.  He checked the rise between the return and supply and that was 40 degrees.  The static pressure was .6.  He looked at the ducts.  His conclusion was that the furnace is just getting older and the airflow just isn’t enough.  So, maybe first guy was right.  I still think the draft induction motor might be a culprit - maybe it’s just a tad weaker?? He checks the amps on it though and it isn’t drawing more amps. I dunno.  It’s a good thing I probably won’t need it again for a little while

coby

the furnance is oversized for the house and ductwork.

coby

pecmsg said:

All units manufactured after 2010 have ECM motors!

After july 2019. All furnaces had to have ECM motors.

cannelg

Even though it isn’t the thermostat, I’d like to replace it anyway.  Was thinking about it even before this. The wiring seems straightforward but there is an orange wire going in the thermostat going from Rh to D1.  It looks like  a jumper wire in the thermostat itself.  What is that for?

Jon_blaney

Does this furnace have a two stage gas valve?

cannelg

Jon_blaney said:

Does this furnace have a two stage gas valve?

No. Just one.  2 stage cooling but one stage gas.

that connect plate is in the air handler closet and only two wires go to the actual user interface of the thermostat, but I think that is to give the thermostat a lower profile . I assume I’ll have to wire nut the wires together here so the ones at the user interface work.  But - this wire just looks like it is Jumped between these two terminals instead of going to the control board or condenser unit. 

mattmia2

Do you have a humidifier? I think that might have been going to hum on the old board to turn on the humidifier on a heat call and now it is making a low dehumidify call on a heat call and running the blower at low speed

Er, never mind that is the thermostat. Dont know what that is doing but it seems wrong

Jon_blaney

I agree with COBY. The furnace is too large for the ductwork and probably the house. Larger duct work will probably cause short cycling. The furnace needs to be replaced with a smaller unit. Get someone who knows what there are doing this time.

wmgeorge

Well the Manual J calc someone left on the job, hopefully the correct one proves that. He has a 100,000 BTU furnace on about a 40,000 BTU load. He could remove the two outside burners, cap off the office's and make sure the ignitor is on the correct burner.
Math on Flex duct? It depends on who installed it. No one has looked at the air entering side of the A coil.

mattmia2

Ed did the math on the ductwork. Although the furnace is probably oversized it has adequate ductwork and the problem just showed up after working with that ductwork for 8 years.

What filter are you using? Did anyone look at the entering air side of the ac coil yet, between the furnace and the coil? Typically it will look completely clean on the exiting air side when the entering side is completely clogged.

cannelg

mattmia2 said:

Ed did the math on the ductwork. Although the furnace is probably oversized it has adequate ductwork and the problem just showed up after working with that ductwork for 8 years. What filter are you using? Did anyone look at the entering air side of the ac coil yet, between the furnace and the coil? Typically it will look completely clean on the exiting air side when the entering side is completely clogged.

 Visible inspection - no.  He tested the pressure and it was .6 - but I have no idea what that means. Lol 

Both techs ended up concluding that airflow is the issue.  I ran it without any filters and it still shut off.

the big question for me now is the need for a 5 ton.  It is 2600 ft in Florida.  It’s hot and humid most of the time down here.  First tech feels it’s overkill.  2nd tech said it is right. 

After we upgraded the unit our electric bills went way down, so the cooling side seems ok.  So I dunno.  If we need a 5 ton, I’ll do what I have to for the airflow.  But I don’t know if it is better to just wait for the unit to die and put in a smaller one or fix this airflow and keep the larger one.  

Jon_blaney

Bees, aligator, or homeless person living in the supply duct?

mattmia2

mattmia2 said:

Did anyone look at the entering air side of the ac coil yet, between the furnace and the coil? Typically it will look completely clean on the exiting air side when the entering side is completely clogged.

If the ac has a txv it will probably tolerate the reduced airflow ok.

cannelg

This is going to sound more confusing that it is, but I am hoping you can help make sure I did this right.  I put in a new thermostat. 

Old one had black wires on Y1/W2 and yellow wire on Y/Y2.

new thermostat only has options for Y and Y2.

so I hooked it up like this.

black - Y
yellow - Y2

Is it correct?

incidentally, I tested it and this thermostat also shuts off when the heater trips the code.  Has it been wired wrong all this time or is that supposed to happen?

mattmia2

I would disconnect the stat and connect r(or rh) to w and see if it still shuts off. I dont think it is the stat but you have some weird wiring that could be forcing it to low blower on a heat call

cannelg

mattmia2 said:

I would disconnect the stat and connect r(or rh) to w and see if it still shuts off. I dont think it is the stat but you have some weird wiring that could be forcing it to low blower on a heat call

I’ve tried that before and it still shuts off.  And the tech swapped the blower speeds on the control board and it still shut off.  Lol - I dunno at this point.  It’s gotta be airflow or the limit switches test good but are too sensitive, or the draft induction fan is too weak but not weak enough to be evident.  

Either way, did I hook that up right?  I’d hate to have that reversed.  Lol - the wiring for that other stat is weird.  

Jon_blaney

The install manual is available on line. It gives complete thermostat wiring directions.

cannelg

It’s more of the old wiring I was unsure about, but I found this from the old thermostat manual:

Based on this, the wire that went to y1/w2 should be considered Y and the wire that went to Y/Y2 should be considered Y2. (The title is underneath the diagram, 1 stage furnace, 2 stage air conditioner)

Btw - thank you to all of you who have helped.  It’s still a puzzle to me.  It’s probably airflow but it is illogical that it is just now having a problem.  The last tech that came out said the thermostat should not be turning off when the heat shuts off as the furnace is still getting power.  The first tech didn’t seem bothered my it.  ???

I feel like there is an answer to this issue but wish there was a way to prove the theory before doing anything.  

mattmia2

If the inlet side of the ac coil is dirty it would explain the airflow suddenly changing. I'm pretty sure it is set up as an upflow furnace even though one of your pictures i think shows it as downflow.

Oh, i see now, you are showing one of the partitions as panned to be the return duct.

cannelg

So I did a little more research. It is normal for the Stat to turn off when the limit switch trips. So, that isn't anything to worry about.

I am still at a loss for this. I think it has to be airflow at this point. Only other thing to check is bottom of coil but I just don't think that is the issue. The blower fan cage is clean. I guess I could buy a scope from amazon and see if I can look under. Nothing else is blocked that I can see, but the logic of it just happening now baffles me. SOMETHING has to be different.

Again, I appreciate everyone's thoughts on this. Great forum this is.

mattmia2

since that return looks a little sketchy you might look for something that came loose in the supply or return or got sucked in to either.

cannelg

Soooo...I am up at 5:11 cause I didn't sleep last night. After changing the thermostat yesterday afternoon, the heater still kept shutting off. Now keep in mind I've tried running this without ANY filters in the returns at all and it still shut down. But I bought some cheap Merv 5 filters just to help out the Cooling side when it gets hot again. I stuck one in last night before I went to bed. I also went to one closet that had a box on the top shelf under the vent that has been close enough to make me think about it moving it, but wasn't really blocking it. The louvers push the air away from it and there was a good amount of space between the box and the vent. Still, I moved it anyway just to see. Then I tried to go to sleep. Heat kicked on, and stayed on. Thought it was a fluke. But it has worked all night. I know, cause I've been up all night.

I sincerely doubt it was the box blocking the vent. It is a small, 4 inch vent in a closet and there was definitely room between it and the vent- I could see the whole vent looking up at it. But maybe?? Or it was the thinner filter, but not sure why that would work when removing it completely didn't. Or a combination?

Was also thinking...the math worked out to where the return CFMs were 2000 and the Supply CFMs were a little over 1700. That seems high if this was originally a 3.5. I KNOW the 5 we put in is bigger. Maybe we originally had a 4 or 4.5? 8 years ago is a long time. One thing about Florida builders, they would not have put in anything extra, so maybe our duct work doesn't need to be redone?

mattmia2

This vent in the closet. Is the closet it goes in to sealed or does it have a louvered door or both a supply and return in the closet? Did you leave the door open after you moved the box?

Oh, one more thought, could something be causing a supply to be sucked in to a return instead of circulating through the room so the return air it much warmer than designed?

cannelg

I did leave the door open and it isn't always open.  I might experiment with that.  And it’s crowded in that closet. I think adding a few supplies may be the long term fix.  Is the goal to have the supply cfm march the return cfm?  

mattmia2

If the supply is in a closed off room with no return it might as well be closed of itself. You can possibly undercut the door to let air pass underneath it but just one blocked supply shouldn't throw the whole system off.

cannelg

If I get the duct work adjusted, they would increase size of supply plenum, change the 3 supply ducts that go to the distribution boxes to 14”, and increase change out the distribution boxes for bigger ones.  My two questions are:

1) Based on everything so far and the ducts I already have, is it necessary?  I can make sure to leave that shelf empty and closet door open in the 8 cold nights we get down here 🤣. Does doing this help the unit run more efficiently even on the AC side?

2.  Will those changes really help if they still feed the same vents/ducts from the distribution boxes to the rooms?  I can see how having more duct room might help, but up until that point, but leaving the distribution boxes, doesn’t that same bottleneck occur?  

Thanks for educating me.

mattmia2

The thing to do is to measure the temp of the air coming in to the furnace and the air going out. The ratings plate will have a maximum temp difference between the 2 and a maximum outlet temp.

One outlet really shouldn't make the difference between tripping the high limit or not. What do the grills on the outlets and returns look like? Are they covered in many layers of paint or dirt or dirt mixed with paint? Are the dampers at the registers open? Are the balancing dampers in the ductwork wherever they are mostly open?

Making some of the ductwork bigger but not all of it will have an effect because air is compressible. You can think of each section as having some resistance to flow, bigger sections have less resistance, smaller sections have more resistance and the total of all those sections is the resistance the blower sees(after it branches each of those sections has a resistance that combines but as something like the inverse of the sum of the inverses). The upshot is if you reduce the resistance anywhere you reduce the resistance the blower sees.

cannelg

It's Florida - today the air is on. LOL The temp difference was only 40 degrees when the last guy was here. It was within the range.

OK...That helps. So if we do this it should help. I appreciate it. I'd rather make sure the system is functioning without any issues so we don't ware it prematurely.

I haven't bothered to shut that door or put that box back up on the shelf. I guess I don't want to jinx it. Not sure when we'll need heat again, so justifying payments for just heat isn't worth it. But if it will ensure the whole system will just run better in general, it might be worth it.

I appreciate your support.

cannelg

Is this right?

I wanted to make sure I wired the thermostat right. I think I did - but - I am curious about the connection in the outdoor unit. If I trace the wires back, Y1 (Black wire) is connected to a blue wire. And Y2 (Yellow wire) is connected to a yellow wire in the unit outside. C (Blue) is connected to a Brw/Yellow wire. I'll attach the schematic and a pic. It's a 2 stage Bryant compressor. Should those be switched?


That yellow wire goes to the contactor and the blue one goes to inside the unit to the bottom..