HVAC stopped running temporarilly, smells of crayons

[dullard]

I got home tonight (too late to call a repair shop) and the house was 15°F colder than normal. Upstairs there was a faint but noticeable smell of crayons.

I checked the thermostat: set to proper temperature, fan on Auto, set to heat pump (I have a gas furnace as emergency heat). It has been reaching just below 0°F here at night with some highs of about 5°F, so the heat pump was sufficient but near its limit. No air was coming out of the vents. Switched the fan to On, still no air came out.

I switched it to emergency heat, the flames started up, but still no hot air coming out of the vents. The gas flames automatically turned off after a minute when it sensed nothing was happening.

I turned off the furnace and set the thermostat to off. I have heard that coils can freeze up and need time to thaw. So I let it rest a bit. 30 minutes later, turned the furnace back on and set the thermostat to emergency heat. Everything works just fine.

Did the coils just freeze up, is it a dying capacitor, or what? Obviously I'll call a technician tomorrow morning. The whole system is probably near its life end as several things have been dying on it over the last few years (a circuit board, the CO exhaust fan, the heat pump fan capacitor, and the heat pump fins are shot from the previous owner's dog's acidic urine). So maybe if I can limp it along a couple of weeks and just replace it that will be good enough.

 

[disappoint]

I kept thinking your 4 year old stuffed crayons into the furnace, because the furnace temporarily morphed into a giant robot from teh planet gobledygook and feeds on crayons for dessert. But no. I leave disappointed.

*I have no idea if you even have kids.

 

[zerocool84]

Check for mice

 

[bbhaag]

Well something was melting if you smelled crayons. Hard to say what without being there. Kind of weird that the blower wasn't working though.
Either way glad the emergency furnace kicked and you have some heat. It's a cold night to go without.

 

[Red Squirrel]

If you open up the furnace panel you should see a fan that connects to black ABS pipes coming out of the furnace. Is it spinning when the furnace starts up? If yes, what about the main blower at the bottom? Though in your case it's probably stopping before it gets to that stage, try putting fan to on just to test it.

I'm not an HVAC tech so I could be way off here but if I had to guess, something in the steps of startup is failing so it's going into safety shut off. Basically when a furnace starts up in starts by fireing the flame then from this point it's doing a series of test like making sure the flame is present (and not just spewing gas that's not burning) then it checks that the draft inducer motor is running (the black one that connects to the ABS pipes) and does other tests. I'm going to guess if the main blower fails to start that would then cause the furnace to shut off as the heat exchanger would be getting too hot. If that is what is happening it could explain the crayon smell. Maybe some kind of rubber seal is melting or something.

 

[compuwiz1]

You humans, have some really strange problems.

If it smells like a crayon, or a rat, it is usually one or both. Someone might have taken a dump in a vent. It happens. I had a young one before.

 

[Red Squirrel]

My cat pukes on the vents sometimes. That is NASTY. The nice thing with a whole house humidifier though is that it can also act as a whole house air freshener. Just dump some bleach or vinegar in there and run it full pin and it gets rid of any nasty smells in the house. Also cleans it at same time.

 

[dullard]

Furnace turned off again overnight. But it was warm enough through the night to sleep. I shut it off again for 30 minutes and it is running again. The furnace is almost 16 years old, time to start shopping.

No kids or pets have been in the house for at least the last 8 years. I vacuumed out the vents about a year ago and removed many toys. No crayons though.

 

[dandruff]

and set the thermostat to emergency heat. Everything works just fine.

No.
You do not understand (and million others dont either - I hate the EH button) the use for EH button on the thermostat. atleast you used it in an actual emergency.

>>> Switched the fan to On, still no air came out.
Fix this.

>>> The whole system is probably near its life end ..
No. Sixteen year for a heatpump system is not end of life.

 

[Eug]

Furnace turned off again overnight. But it was warm enough through the night to sleep. I shut it off again for 30 minutes and it is running again. The furnace is almost 16 years old, time to start shopping.

Call an HVAC guy. I had a similar problem and it was a dying motherboard. $500 fix but better than a new furnace.

Mind you I replaced the furnace anyway a few years later anyway for other reasons.

 

[iwajabitw]

Have a tech come look at it, several things can cause the blower to not run, tstat, sequencer, capacitor, fan relay, transformer or limit switch depending on what model you have. The smell could actually be that the motor has gone out and your gas fired up to try and help the heat pump reach temp. But with out the blower running the high limit switch kicked the gas off to prevent ruining the exchanger. Get a tech out there, don't want to damage something over whats usually a small electrical part. HVAC guy for 20yrs.

 

[dullard]

I do have an HVAC guy coming over, but it'll be another couple of hours. This thing breaks every year with a different problem. And it is just 78% efficient (when new, probably far lower now). Why should I keep dumping in $200+ a year vs just replacing it?

 

[MongGrel]

Sounds to me it might need replacing, I finally bit the bullet with my old one last year and it's actually saving money now of course.

Had one I babied along that was 25 years old and had even replaced an air handler, wish I had just replaced everything then.

Even bought a heat pump half ton higher than recommended.

Just my two cents.

You're on gas so different, but still.

 

[Genx87]

I had an issue like this a couple years ago. A controller took a crap. When the system would turn on and run its checks the controller would fail and turn off the system. We replaced the controller and it has bee working since. It is also a old unit. I think 17 years old now? What brand and model do you have?

 

[iwajabitw]

I do have an HVAC guy coming over, but it'll be another couple of hours. This thing breaks every year with a different problem. And it is just 78% efficient (when new, probably far lower now). Why should I keep dumping in $200+ a year vs just replacing it?

Have load calculations and an energy audit done on your home and have a new unit priced. High efficient units are only as good as the install/installer. Strapping a new unit onto existing duct work, usually too restrictive, will not improve anything. This would give you a base line on whether or not a new unit vs yearly service is best. A new system could run from $4k-$10k based on the load cals and whether you need new duct work to accommodate the unit.

 

[iwajabitw]

Had one I babied along that was 25 years old and had even replaced an air handler, wish I had just replaced everything then.

Even bought a heat pump half ton higher than recommended.

Just my two cents.

Be careful about oversizing. In the HVAC world it usually a bad thing causing short cycles to the unit prematurely ruining compressors. There made to run 24/7 so long cycles are best for the home for latent heating and cooling. In the south AC's are grossly oversized for cooling and this causes a lot of mold issues in homes because it never runs long enough to drop the humidity in the house. In winter a heat pumps takes at least 10-20min to get up to nominal temp rise. Just a FYI.

 

[dullard]

What brand and model do you have?

Amana 80 SV. I would assume the 80 is efficiency from the name, but there is a 78% efficiency sticker on it as well.

As I was looking at it closer, there is a couple of tablespoons of rust in the drain line. The thing flooded last year when the drain line clogged and the electronics were submerged. Replacing the drain lines and drying everything out got it to run one more year. But I wonder if the rust is a bad sign or pretty normal.

The HVAC guy replacing the exhaust motor in 2012 said we should have replaced the whole unit then. But, then he may have been just trying to upsell us.

 

[iwajabitw]

Amana 80 SV. I would assume the 80 is efficiency from the name, but there is a 78% efficiency sticker on it as well.

As I was looking at it closer, there is a couple of tablespoons of rust in the drain line. The thing flooded last year when the drain line clogged and the electronics were submerged. Replacing the drain lines and drying everything out got it to run one more year. But I wonder if the rust is a bad sign or pretty normal.

The HVAC guy replacing the exhaust motor in 2012 said we should have replaced the whole unit then. But, then he may have been just trying to upsell us.

The rust could be off of the cabinet where it got wet and the paint flaked off. And don't buy a unit unless load cals are done, other wise your just throwing money at it. You need to hear terms like Manual J, D etc..have the static pressure of the unit and duct system checked to see if its restricting air flow with a manometer or magnahelix. There are so many things, insulation, windows, flooring etc that contribute to heat loss. I wouldn't buy any unit from a company that will not give you load cals. Its such a big purchase you want it to be worth it and pay you back. A good company can make a cheap unit run better than the best brand/system on the market if it was installed poorly. Good luck and shop around until you get all the info you can.

 

[Eug]

Have load calculations and an energy audit done on your home and have a new unit priced. High efficient units are only as good as the install/installer. Strapping a new unit onto existing duct work, usually too restrictive, will not improve anything. This would give you a base line on whether or not a new unit vs yearly service is best. A new system could run from $4k-$10k based on the load cals and whether you need new duct work to accommodate the unit.

Be careful about oversizing. In the HVAC world it usually a bad thing causing short cycles to the unit prematurely ruining compressors. There made to run 24/7 so long cycles are best for the home for latent heating and cooling. In the south AC's are grossly oversized for cooling and this causes a lot of mold issues in homes because it never runs long enough to drop the humidity in the house.

An AT forum member real world example for the end users here (like me):

Based on calculations done by an HVAC engineer, with some duct changes as part of the design recommendations, I went from a 100000 BTU single stage furnace to a 70000 variable stage. The new setup had an upsized return duct from the top floor and a partially upsized supply duct too.

2.5 ton AC in previous system was insufficient. 2.5 ton AC in new system (with updated ducting) is sufficient. My HVAC guys told me my main problem was the return duct. The previous system worked well enough for heating (with an oversized furnace), but just couldn't cut it for cooling. Note that the duct design was a compromise, because the HVAC engineer said some of the other existing ducts were still undersized, but I wasn't going to rip all those out.

This living space is around 1800 square feet main 1st and 2nd floors (moderately high to high ceilings), with around 800 square feet in the basement (low ceiling). House is moderately leaky for a modern home, with lots and lots of windows, but much less leaky than most century homes.

 

[dullard]

Update:

Furnace replacement quote: $2124 for Trane XR80, or $3168 for XV80 (variable speed fan). Price-wise the quick furnace swap isn't too bad. I don't think the variable speed fan is worth $1044, unless anyone knows of a reason to persuade me otherwise.

Blower replacement quote: $289.

So, while waiting for my wife to come home to discuss it, I went out and bought a replacement run capacitor for the blower for $13.99 (a ripoff for a $1.50 part, but what do you expect on a weekend for an HVAC part). Its been running flawlessly for over an hour now.

 

[disappoint]

Capacitors are made of crayons!

Just kidding, thanks for the update!