Furnace smell

[TravelTiger]

Erika,

I re-looked at my old furnace and mine is not discolored like the top left of yours. It definitely looks like it's overheating in that area of the heat exchanger. Not sure why it would overheat in just that area, but it is right after combustion. Here's some interesting reading...Link

Thanks Rex. I've sent that same pic to Suburban, that expressed discoloration is normal. I tend to disagree based on how little this furnace has been used by us, but hopefully a tech can pull it out and do some actual testing.


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[rxbristol]

A couple of questions:

1. Does the motor fan continue to run after the furnace flame as quit so to cool the heat exchanger down? It should run for about 1-2 minutes.

2. How forceful is the air coming out of the vents? I know this is a tough question, but I wonder how fast the motor is running to prevent overheating.

3. When it cycles, how long between them?

4. Make sure the blue wires are connected correctly. Blue/white wire should be connected to black/white wire--this is positive and goes to the on/off switch. The other blue wire should be connected to the white 18 gauge wire which goes to the limit switch through the sail switch on to the motor. Also, check to make sure the red 14 gauge wire is connected to the white/green wire and the white 14 gauge wire is connected to the yellow wire. I may be wrong, but if one set of those wires are reversed the motor may run backwards which would still provide enough flow to close the limit switch, but limit flow to the RV causing overheat in the exchanger...armchair troubleshooting.

 

[TravelTiger]

See my responses:

A couple of questions:

1. Does the motor fan continue to run after the furnace flame as quit so to cool the heat exchanger down? It should run for about 1-2 minutes.

Yes.

2. How forceful is the air coming out of the vents? I know this is a tough question, but I wonder how fast the motor is running to prevent overheating.

Fairly forceful. The unit heats the rig very well.

3. When it cycles, how long between them?

Depends on the setting/temp, I'm not really sure, but nothing seems out of the ordinary.

4. Make sure the blue wires are connected correctly. Blue/white wire should be connected to black/white wire--this is positive and goes to the on/off switch. The other blue wire should be connected to the white 18 gauge wire which goes to the limit switch through the sail switch on to the motor. Also, check to make sure the red 14 gauge wire is connected to the white/green wire and the white 14 gauge wire is connected to the yellow wire. I may be wrong, but if one set of those wires are reversed the motor may run backwards which would still provide enough flow to close the limit switch, but limit flow to the RV causing overheat in the exchanger...armchair troubleshooting.

Regarding the wiring, we'd have to take it apart again. Maybe this weekend.

We are managing to use the furnace very little. Even when it got to about freezing last night, we only had to run the furnace one time early in the morning, to get the temp up a little and then use our fireplace and other heaters to get it comfortable as the sun came up and warmed the day.


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[TravelTiger]

Well, the RV tech was out here today, and could definitely smell the smell, but he was not sure what caused it. Anyway, we called Suburban as they asked, and were pleasantly surprised that they were authorizing a NEW FURNACE to be sent to the RV tech! So hopefully late next week we'll know if it was in fact an issue with this the furnace or some other anomaly.

YAY!!!

 

[olcoon]

That's GREAT! At the least you are getting a new furnace for free!

 

[TravelTiger]

That's GREAT! At the least you are getting a new furnace for free!

Well, not free. I still have to pay the trip charges for the mobile tech. But that's worth it to us!


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[rxbristol]

May your new furnace be smell free like our new one.

 

[TravelTiger]

New furnace is in. Waiting for the "new" smell to go away. Hope it works, supposed to be 17 tonight!

Pics of the old one:

Sorry I don't have better pics than this. I didn't really get to examine it closely.


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[JohnDar]

Looks pretty scorched to me.


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[CoveredWagon]

Something is seriously wrong there. Here’s hoping for you.

 

[TravelTiger]

Well the problem is not completely solved. Still have some burning plastic-like smell after unit runs about 5 minutes. Now beginning to wonder about the ductwork materials.


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[JohnDar]

Well the problem is not completely solved. Still have some burning plastic-like smell after unit runs about 5 minutes. Now beginning to wonder about the ductwork materials.


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If I was nearby (Michigan is kinda far away), I'd use my Laser Thermometer to see what kind of temps you're getting at the duct inlets and the surfaces of the furnace. FWIW, Harbor Freight has (or had) them for about $50.

When you had the furnace out, were you able to take a look at the ends of the ducts where they connect to the unit? Any melting, discoloration, or embrittlement? Possible what you're smelling with the new furnace is residual from the previous one left in the ducts. Maybe it will clear with use.

 

[TravelTiger]

If I was nearby (Michigan is kinda far away), I'd use my Laser Thermometer to see what kind of temps you're getting at the duct inlets and the surfaces of the furnace. FWIW, Harbor Freight has (or had) them for about $50.

When you had the furnace out, were you able to take a look at the ends of the ducts where they connect to the unit? Any melting, discoloration, or embrittlement?

Previously, we took the ducts off the back and looked in the housing, as you see in previous posts.

The housing and ducts were not touched, only the "innards" were replaced. (Disconnect 3 wires and the propane, loosen a screw and it slides right out.)

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[JohnDar]

So much for my S.W.A.G.'s. Does the smell come out of all of the ducts when you turn it on or can you localize it to a single duct/register? No excess duct or bends near the furnace? With ours, back when, I had to cut almost 4 feet of duct off the bedroom line to get a semi-straight run. Added a flexible metal elbow to the register inlet to keep it straight. Didn't have any plastic smell, though.

 

[TravelTiger]

We have a thermal gun as you mentioned. My temps at the ducts: living - farthest run 118. Kitchen (has some kind of box to make it come out of the pony wall in kitchen), 108. Stairs 128. Bathroom, 121. Bedroom, which actually has duct to bathroom floor and then a metal channel duct in the floor over to the bedroom, 108.

The two black ducts are insulated and go downward quickly from the back of the furnace and to the underbelly toward the back of the rig. The other three are silver material ducts and very short runs to stairs, bath and bed. I took a bunch of slack out of them almost immediately.

To answer the "where is it coming from" it's all ducts, after the unit runs for more than 5 min or so. When the heat kicks off and the fan still running, the smell freshens/goes away. So it's related to heat.

When we took the back off and disconnected the ducts, the smell seemed to be coming from the furnace itself.

Now I'm wondering if it's the black ducts or the silver ducts off-gassing once they get hot.


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[danemayer]

Maybe you could talk Heartland into send you some ducting to replace the ones that are easy to get to.

 

[TravelTiger]

Maybe you could talk Heartland into send you some ducting to replace the ones that are easy to get to.

Dan, that was an idea the tech had before Suburban offered to replace the furnace, but he suggested we find it and try ourselves to see if that was the cause.

It's probably 20 or so feet of the silver ductwork.

I'll email Heartland and see what they say, they have been "in the loop" on this already.




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[CoveredWagon]

Just a thought. You might buy one of those endoscopic cameras, they’re fairly inexpensive, that you could push down either end of the heat tubes and see if you have an obstruction somewhere.

 

[TravelTiger]

Spent part of yesterday removing all the ducts from the furnace housing and examining them, redoing the connection of the lower ductwork with an HVAC elbow to ease the transition and reseal the connections and the insulation jacket with HVAC tape. I also cleaned and wiped down everywhere possible with a natural enzyme cleaner to eliminate any possible urine smell, since we have had some mouse evidence.

Smelling all the vents separately, non-heated, they don't smell out of the ordinary in any way. We reattached all the ductwork, and ran the furnace again. The smell returned overnight as the furnace ran more often.

This morning we'll try replacing the silver ductwork, wondering if that is the culprit. It does smell on the exterior of the duct when it is heated -- but I am dumbfounded why this would be the foul smell source if this is the standard ductwork used in RV manufacturing.


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[rxbristol]

I wonder if by the original furnace overheating it sent enough hot metallic smell/substance into the duct and that is what you're smelling.