Problem - 1986 CARRIER Gas Furnace - fan won't stop and no heat


Old 12-10-18, 08:27 PM
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Problem - 1986 CARRIER Gas Furnace - fan won't stop and no heat

10 December 2018 , Monday

Hello to All:

I have a 32-year-old gas furnace for my 4-bedroom home (2-story).
As far as I know, it's never been serviced and it's never had any problems.
The furnace information is as follows:

Manufacturer: " BOP Company, Division of Carrier Corp. "
Model # : 395BAW060095
Product # : 395BAW060095AABA
Serial # 2486C19069

i'm a complete newbie at anything involving furnace repair. About 1 week ago in the
morning, I turned off my heat at the thermostat. About 1/2 hour later, i was near the
intake vent and I heard the sound of the furnace fan running (albeit, it was not as
strong a "fan sound" as I normally hear. I had an HVAC guy come out and assess the
things: His results: a faulty limit switch and a cracked heat exchange (the heat exchange is a part that cannot be found, he says [!] ). He deemed the furnace un-
safe and offered replacement as my only option

Honestly, I did not trust this HVAC guy - in my opinion, all he wanted to do was to find
some reason/excuse to sell me a new $4500.00 furnace! He wanted to sell me a new
AC unit as well (combined price: $7200.00). His exact verbatim statement on his
paperwork reads :

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Old 12-10-18, 08:36 PM
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my own reply: problem with 1986 CARRIER furnace

How can I DIY this, i wonder? I know the high prices are caused by the labor, so i'm
trying to find out how I can proceed along a less expensive course.

QUESTIONS: can a heat exchanger and limit switch be found as parts for my make
and model furnace? Can a newbie like me install these parts safely? can I buy a new
furnace and then install/connect it myself, thereby saving money on the labor ? are
user manuals available for my make and model furnace?

Any help would help greatly, and I appreciate any input at all


Brian B.
Old 12-10-18, 08:50 PM
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At that age....... the furnace needs replacement. There won't be any replacement heat exchangers around for it.

DIY furnace installation ? I wouldn't recommend it. You need to be skilled in gas, electric and ductwork. After the new furnace gets installed..... commissioning/setup work needs to be done.

My recommendation...... get several estimates. Don't have the companies just replace like for like. Have heat calculations done so that a properly sized unit is installed.
Old 12-11-18, 04:24 AM
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Gas furnaces usually have a cool down function that allows the blower to continue running for a period after the t'stat is satisfied. This allows a heat source without burning fuel. In your case, the limit switch contains adjustable contacts for turning off the blower motor. I am sure replacements are available if needed. Sometimes only a cleaning of the limit switch's heat sensing probe is needed.
A leaking heat exchanger is a source of carbon monixide and should be addressed quickly and safely. Today, make sure all 3 levels of your house have working carbon monoxide detectors. I would get at least two more opinions on the condition of the furnace heat exchanger. If the collected opinion is the heat exchanger is bad, call Carrier to confirm there are no replacements before entertaining a furnace replacement.
Old 12-17-18, 09:19 PM
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17 Dec. 2018

The Gas & Electric guy cam by today: he tested and found the bad
limit switch BUT he took a camera inside every "cell" of the heat box
and found no cracks at all. There wasn't much discoloration either in
the heat box, so he figured the HVAC guy was just trying to sell me a
4500.00 furnace (with a 5000.00 AC soon to follow!)

I have reason to doubt that there is a crack in the heat exchanger.
I want to SEE the crack before replacing the heat box. and I want to have
a carbon monoxide detector check in the duct vents too (i'm told the presence
of CO can imply a cracked heat box

So, the gas/electric guy gave me some advise: he said you can get ANY
parts for the furnaces, including a new limit switch assembly. I feel I could
handle a limit switch installation ��

feedback would be most appreciated, and thank you for your previous reply

Old 12-17-18, 09:58 PM
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As far as the cracked heat exchanger goes they sell what they call "smoke candles". You light them and put them in your chamber and when the blower comes on if you have a crack in the exchanger the smoke will travel through the ductwork and come through the registers.

If no smoke enters the living area then you have a good heat exchanger with no cracks.

Just my opinion but if your exchanger is cracked and even if you could get one, it is very labor intense to replace one, if you could find someone to do it and would be very cost prohibitive and at this time of year it is no job for a DIYer. All things be equal it would actually take you less time to replace the furnace than to replace the heat exchanger.

As for the fan/limit switch, as the gas guy said, I'm sure they are readily available and that is something that you most likely could handle yourself if you have any kind of mechanical ability are not afraid of electricity and use common sense.

Pics would be helpful if you need help locating one. Below is a sight for your smoke candles. I'm sure there are others but this is just to give you some options and show you what they are. The gas guy may even have them.

Hope this helps a little.
Old 12-20-18, 03:50 PM
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we have 7-8 carbon monoxide alarms throughout our house, upstairs
and downstairs and in the garage close to the furnace. None have ever
gone off. Isn't this a pretty good test too to rule out leaks in the
heat box?
Old 12-20-18, 07:07 PM
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Location: San Jose,Ca
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Years ago we used sulphur sticks. Put on the burner and then go around and smell the supply registers. Only problem was almost every one had an odor. If you haven't guessed why....the odor was on our fingers. Lesson learned
Old 12-20-18, 08:45 PM
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1. When a limit switch fails, it can be due to being cycled due to overheating too many times. There may be an underlying problem

2. CO alarms provide a false sense of security and will not detect a cracked heat exchanger unless the problem is really bad. By the time one goes off, you've already been poisoned, perhaps chronically

3. You'll need a new furnace soon. Your heat exchanger will crack at some point, they all do from being expanded and contracted thousands of times each heating season

It's at the end of it's life!

$4000 is not unreasonable for a new furnace depending on the amount of work required and what model you get.
Old 12-21-18, 05:12 AM
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Hardware and big box store CO detectors will not save you from harm. They are purposely set to trip at a high level to avoid nuisance trips. The trouble is by the time it goes off you could already be unconscious from CO poisoning. Low level CO detectors are what you want, although they are very expensive.
A CO detector will not alert you to a cracked heat exchanger.
Your furnace is 33 years old. And gets used for many cycles every day all during heating season. It’s past it’s prime.
Make sure if the furnace is replaced a load calculation is done to correctly size the replacement furnace.

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