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Old 02-06-2020, 04:32 AM   #31
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Re: Bryant plus 80t furnace power issue?


The top side can be shiny, while the bottom side is very dirty.
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Old 02-06-2020, 11:46 AM   #32
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You need to check near the furnace, not at the vents.

You need a proper thermometer that can read well above 110F -> cooking/lab.



It gets inserted into the supply duct near the furnace, but not in line of site of the heat exchanger.

The return air was 77 and supply air is 133. I let the furnace run for 8 to 10 minutes before taking the readings. That's with a new merv 2 filter.
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Old 02-06-2020, 02:15 PM   #33
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Re: Bryant plus 80t furnace power issue?


Was that on low or high fire?

Most 2-stage furnaces run hotter on high fire, especially the ones with non-ecm blower motors.

You need to check high - it may only be tripping the limit on high.
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Old 02-07-2020, 11:58 AM   #34
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Originally Posted by user_12345a View Post
Was that on low or high fire?

Most 2-stage furnaces run hotter on high fire, especially the ones with non-ecm blower motors.

You need to check high - it may only be tripping the limit on high.
Those last results were on low fire. I did another test this morning on high fire and it was 154 supply and 74 return. It is deffinatly in 30 to 60 rise.
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Old 02-07-2020, 12:19 PM   #35
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Re: Bryant plus 80t furnace power issue?


It's way too high.

What size is the furnace? (full model number helpful to determine blower capacity)

Are you using a 1" pleated filter and if yes, what size and type/merv rating?

Pull the filter out, close the access slot and see if the temperature rise drops a lot.

The gas meter should be clocked with all other appliances off to rule out an over-firing condition. Need the btu content from your gas supplier and don't use the fastest dial.

Instructions: https://hvactechhangout.com/home/sys...k-a-gas-meter/

The coil may be producing an excessive pressure drop due to dust/dirt buildup and should be checked-> hard to do and can require a snake camera or a checking pressure drop with a manometer.

(you may be able to see it if the blower is pulled and you look up, but probably not)

If there's no apparent cause, may be able to raise the fan speed but I doubt you will be able to get it from 80 to the 60s with that alone. Usually going up one speed only drops the rise by 2 to 5F and it's probably already on medium high.

There is a chance the furnace is just grossly oversized for the house and ducts in which case it's best to just disable high fire.
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I am not in the business of any trade I give advice on. I have non-professional hvac experience + good knowledge of theory. Attempt repairs at your own risk. Never jump out safeties - especially pressure switches - on a furnace for testing with fuel supply on; use a meter. Do not troubleshoot with live line voltage present unless there's no alternative.

Last edited by user_12345a; 02-07-2020 at 12:27 PM.
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Old 02-07-2020, 12:53 PM   #36
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Quote:
Originally Posted by user_12345a View Post
It's way too high.

What size is the furnace? (full model number helpful to determine blower capacity)

Are you using a 1" pleated filter and if yes, what size and type/merv rating?

Pull the filter out, close the access slot and see if the temperature rise drops a lot.

The gas meter should be clocked with all other appliances off to rule out an over-firing condition. Need the btu content from your gas supplier and don't use the fastest dial.

Instructions: https://hvactechhangout.com/home/sys...k-a-gas-meter/

The coil may be producing an excessive pressure drop due to dust/dirt buildup and should be checked-> hard to do and can require a snake camera or a checking pressure drop with a manometer.

(you may be able to see it if the blower is pulled and you look up, but probably not)

If there's no apparent cause, may be able to raise the fan speed but I doubt you will be able to get it from 80 to the 60s with that alone. Usually going up one speed only drops the rise by 2 to 5F and it's probably already on medium high.

There is a chance the furnace is just grossly oversized for the house and ducts in which case it's best to just disable high fire.
Bryant Model 312AAV036070AEJA

Currently I installed a Merv 2 basic filter. The air intake is pretty small 14x14x1. The overheating never was an issue it seems until I completely insulated my plaster walls in my living room and stock all the air drafts.
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Old 02-07-2020, 01:00 PM   #37
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Quote:
Originally Posted by Indyman317 View Post
Quote:
Originally Posted by user_12345a View Post
It's way too high.

What size is the furnace? (full model number helpful to determine blower capacity)

Are you using a 1" pleated filter and if yes, what size and type/merv rating?

Pull the filter out, close the access slot and see if the temperature rise drops a lot.

The gas meter should be clocked with all other appliances off to rule out an over-firing condition. Need the btu content from your gas supplier and don't use the fastest dial.

Instructions: https://hvactechhangout.com/home/sys...k-a-gas-meter/

The coil may be producing an excessive pressure drop due to dust/dirt buildup and should be checked-> hard to do and can require a snake camera or a checking pressure drop with a manometer.

(you may be able to see it if the blower is pulled and you look up, but probably not)

If there's no apparent cause, may be able to raise the fan speed but I doubt you will be able to get it from 80 to the 60s with that alone. Usually going up one speed only drops the rise by 2 to 5F and it's probably already on medium high.

There is a chance the furnace is just grossly oversized for the house and ducts in which case it's best to just disable high fire.
Bryant Model 312AAV036070AEJA

Currently I installed a Merv 2 basic filter. The air intake is pretty small 14x14x1. The overheating never was an issue it seems until I completely insulated my plaster walls in my living room and stock all the air drafts.
14x14x1
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Old 02-07-2020, 01:26 PM   #38
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Quote:
Originally Posted by Indyman317 View Post
Quote:
Originally Posted by user_12345a View Post
It's way too high.

What size is the furnace? (full model number helpful to determine blower capacity)

Are you using a 1" pleated filter and if yes, what size and type/merv rating?

Pull the filter out, close the access slot and see if the temperature rise drops a lot.

The gas meter should be clocked with all other appliances off to rule out an over-firing condition. Need the btu content from your gas supplier and don't use the fastest dial.

Instructions: https://hvactechhangout.com/home/sys...k-a-gas-meter/

The coil may be producing an excessive pressure drop due to dust/dirt buildup and should be checked-> hard to do and can require a snake camera or a checking pressure drop with a manometer.

(you may be able to see it if the blower is pulled and you look up, but probably not)

If there's no apparent cause, may be able to raise the fan speed but I doubt you will be able to get it from 80 to the 60s with that alone. Usually going up one speed only drops the rise by 2 to 5F and it's probably already on medium high.

There is a chance the furnace is just grossly oversized for the house and ducts in which case it's best to just disable high fire.
Bryant Model 312AAV036070AEJA

Currently I installed a Merv 2 basic filter. The air intake is pretty small 14x14x1. The overheating never was an issue it seems until I completely insulated my plaster walls in my living room and stock all the air drafts.
14x14x1
With filter out on high fire sippy is 146 and return 69
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Old 02-07-2020, 03:14 PM   #39
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Re: Bryant plus 80t furnace power issue?


The filter and return inlet are severely undersized.

Filter should be like 16x25 - and bigger is better.

Any other filters/return grills?

The entire return side of the system could be undersized.



Best to rule out other things anyway - You may have multiple issues.:

Do clock the meter anyway to rule out over-wiring.

Also see which speed is wired for high heat - schematic on blower access panel shows connections and wire color vs speed.

Is the unit in a basement or mechanical room - upflow or attic, crawlspace - horizontal?


Why you may not have noticed before:

For the furnace to stop working and lock out, the limit has to trip a few times - each time, the fan continues to operate to cool off heat exchanger.

Further, if it's only happening on high fire, you won't see it unless you're raising the temp up or it's really cold outside.

Doing plaster work may have put out a lot of dust, causing enough buildup on the indoor coil to make the problem bad enough to be noticeable.
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I am not in the business of any trade I give advice on. I have non-professional hvac experience + good knowledge of theory. Attempt repairs at your own risk. Never jump out safeties - especially pressure switches - on a furnace for testing with fuel supply on; use a meter. Do not troubleshoot with live line voltage present unless there's no alternative.

Last edited by user_12345a; 02-07-2020 at 03:31 PM.
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Old 02-07-2020, 04:20 PM   #40
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Quote:
Originally Posted by user_12345a View Post
The filter and return inlet are severely undersized.

Filter should be like 16x25 - and bigger is better.

Any other filters/return grills?

The entire return side of the system could be undersized.



Best to rule out other things anyway - You may have multiple issues.:

Do clock the meter anyway to rule out over-wiring.

Also see which speed is wired for high heat - schematic on blower access panel shows connections and wire color vs speed.

Is the unit in a basement or mechanical room - upflow or attic, crawlspace - horizontal?


Why you may not have noticed before:

For the furnace to stop working and lock out, the limit has to trip a few times - each time, the fan continues to operate to cool off heat exchanger.

Further, if it's only happening on high fire, you won't see it unless you're raising the temp up or it's really cold outside.

Doing plaster work may have put out a lot of dust, causing enough buildup on the indoor coil to make the problem bad enough to be noticeable.
Would it help if I installed another filtered air return vent oh say 16x6, thats about all I have room for on the side of the air return box. This house is about 650 sq ft and the furnace is exactly right in the middle of the house in the kitchen and it's upright. I wanted to update on the whole lockout issue where my system was blinking code 33 and losing power for hours, well long story short I replaced all of the old crappy 20 amp breakers in my box with new ones and the system stoped losing power. The system still continues to blink 33 when it hits high fire, it blinks 33 and turns the burners off until the fan cools the system down and then it quits blinking and goes back to normal. When I removed the plaster in the living room I completely turned the a/c and furnace off to keep the system safe so I kept the system off until I completely cleaned all the dust up, so I'm hoping the system didn't get any dust.
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Old 02-07-2020, 05:46 PM   #41
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Re: Bryant plus 80t furnace power issue?


It's a large furnace for a 650 sq ft.

High fire can probably just be disabled completely - granted if you have an a/c greater than 1.5 ton it too may be affected by low airflow and duct mods may be advisable.

That being said, I would not start with duct modifications - should you do mods, the entire duct system should be checked because there's no point of adding another return grill if there are other bottlenecks without fixing everything.

All duct sizes should be checked* and ideally, static pressure testing be done. (requires a manometer, tubes, tips)

*You would have to post a diagram of your duct setup including all sizes.




For now, should rule out the obvious stuff.

I would clock the gas meter on high fire and check the evap coil for dust/dirt buildup. There may be a spacer between furnace and the coil, allowing you to check the underside. (static pressure testing is also useful for seeing if the coil is dirty)

If all checks out, can increase the fan speed for high fire to the highest tap if it's not already there. (a/c may need high as well and there's a way to run both high heat and cooling on the same tap)

I do suspect you'll end up just having to leave high fire disabled; doubt you'll get it down below 60F even if furnace is over-fired and that's corrected and fan speed is increased.

When the furnace needs to be replaced, it can be properly sized based on a load calculation.

Carrier/bryant now makes furnaces down to 26k and i think lennox makes a 30k, or it is a 44k that can be de-rated to 30k with a kit.

Worst case, probably -> 40k btu/hr input @ 90%+ efficient if the house has zero insulation.
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I am not in the business of any trade I give advice on. I have non-professional hvac experience + good knowledge of theory. Attempt repairs at your own risk. Never jump out safeties - especially pressure switches - on a furnace for testing with fuel supply on; use a meter. Do not troubleshoot with live line voltage present unless there's no alternative.
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Old 02-08-2020, 10:54 AM   #42
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It's a large furnace for a 650 sq ft.

High fire can probably just be disabled completely - granted if you have an a/c greater than 1.5 ton it too may be affected by low airflow and duct mods may be advisable.

That being said, I would not start with duct modifications - should you do mods, the entire duct system should be checked because there's no point of adding another return grill if there are other bottlenecks without fixing everything.

All duct sizes should be checked* and ideally, static pressure testing be done. (requires a manometer, tubes, tips)

*You would have to post a diagram of your duct setup including all sizes.




For now, should rule out the obvious stuff.

I would clock the gas meter on high fire and check the evap coil for dust/dirt buildup. There may be a spacer between furnace and the coil, allowing you to check the underside. (static pressure testing is also useful for seeing if the coil is dirty)

If all checks out, can increase the fan speed for high fire to the highest tap if it's not already there. (a/c may need high as well and there's a way to run both high heat and cooling on the same tap)

I do suspect you'll end up just having to leave high fire disabled; doubt you'll get it down below 60F even if furnace is over-fired and that's corrected and fan speed is increased.

When the furnace needs to be replaced, it can be properly sized based on a load calculation.

Carrier/bryant now makes furnaces down to 26k and i think lennox makes a 30k, or it is a 44k that can be de-rated to 30k with a kit.

Worst case, probably -> 40k btu/hr input @ 90%+ efficient if the house has zero insulation.
Ok I got you I'll start with the simple stuff.
It deffinatly seems like high fire is an issue because the air intake can't keep up with demand. I can recall when we always keep the place continuously well heated the furnace never goes into high fire and always stays on low fire without any issues. I won't be able to disable high fire until monday. Do you have any other information on how to disable High fire on my furnace? Appreciate all the information. You've been helpful and tought me some things
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Old 02-08-2020, 11:53 AM   #43
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Re: Bryant plus 80t furnace power issue?


If there's a wire connected to W2, you disconnect and cap it off.

If the staging is timed, there's a dip switch you have to change, it's called low heat only and needs to be set to ON in most cases.

The schematic should show it and install manual has specific instructions.
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Old 02-10-2020, 01:12 PM   #44
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If there's a wire connected to W2, you disconnect and cap it off.

If the staging is timed, there's a dip switch you have to change, it's called low heat only and needs to be set to ON in most cases.

The schematic should show it and install manual has specific instructions.
Here is the Hi and low heat wire. Do I just unplug the blue hi wire? When you say cap it, what exactly do i need to do this?
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Old 02-10-2020, 05:56 PM   #45
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Re: Bryant plus 80t furnace power issue?


So, unplug the blue wire and move the black wire from wherever it's connected now to the high heat connection.

Temporarily connect the blue to where the black was. If it's the cooling connection and you have a 1.5 ton a/c, that's probably where it needs to be based on your temperature measurements.

Calculated 625 cfm and it could be lower than that due to reduce heat output caused by low airflow.

If you have a 2 ton a/c, you'll likely need black for both high heat and cooling and there's a way to put both on the same speed.


After changing the speed, recheck on high fire.

Do clock the gas meter at the same time, with all other gas appliances off to make sure the furnace is not over-fired. Use the 1 cu ft (or greater unit) dial and try to find the btu/cu ft in your area.

It may need a gas pressure adjustment.

Edit:

The schematic shows that blue is medium low, not medium.

I still believe you'll end up needing black on high heat given where the temp rise is now.

As you raise the airflow above what the ducts were sized for, the duct pressure really shoots through the roof
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Last edited by user_12345a; 02-10-2020 at 06:24 PM.
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