Weathermaker furnace not heating, produces a sour smell in exhaust

We have an 18-year-old Weathermaker furnace with what I think is a cracked Carrier heat exchanger. There’s a strong acrid smell coming out the PVC exhaust pipe outdoors. In the past week the fan has been running long after the heat ceases, which forces cold air through the house, until I cut the gas and electric supply to the furnace and press the manual button on the side of the furnace.

I’m thinking about replacing this Carrier furnace because two service people said that a cracked Carrier heat exchanger is a major problem and that carbon monoxide could seep into the house. I should tell you that the air filter is clean and that I had the limit switch replaced recently in an effort to solve the problem of the fan. The fan problem and acrid odor continue. I also see a small amount of condensation / water in the furnace.

I read on the Internet that there was a class action lawsuit against Carrier, that claimed that the secondary heat exchangers have been designed with poor materials and were prone to failure. In the settlement, Carrier was required to replace the secondary heat exchanger where it failed (covering both parts and labor).

Because I don’t really know if that’s the problem … any experts out there who could tell me if this could be it?

Answer from Green Energy Efficient Homes

It sounds to me like your main heat exchanger has cracked, causing the furnace to shut off the heating element but not the fan. That would explain why you are getting cold air blowing through the house – because the thermostat thinks it should still be in heating mode, and so keeps the fan going, but the furnace thinks (probably correctly) that it’s not safe to keep the flame on.

Carbon monoxide poisoning is a very real risk in the case of a cracked Carrier heat exchanger, so if I were you I would not wait long to replace your furnace. I would also make sure you have a CO detector in every bedroom in your house, so if things do deteriorate to the point where your furnace is leaking CO into the house, you know it instantly and don’t asphyxiate in your sleep.

And you are right, there was a class action settlement in both the US and Canada relating to the cracked Carrier heat exchanger problem – concerning secondary heat exchangers, that is. They were made of mild steel and coated with polypropylene instead of the industry standard of stainless steel. I believe many of the heat exchangers that cracked early on (and caused the class action lawsuits to launch) were the result of installers selling oversized furnaces, which tend to cycle more frequently and therefore cause more wear on components.

In any case, the Carrier settlement is not likely to help you out very much because (A) it relates to secondary heat exchangers, and your cracked Carrier heat exchanger is the main heat exchanger, and (B) even if you did have a cracked secondary heat exchanger, your Weathermaker furnace is quite old and the settlement was prorated based on furnace age. Under the settlement, a furnace of your Weathermaker’s vintage with a cracked secondary heat exchanger might entitle you to a couple of hundred dollars towards a new furnace. They may pay the full amount to replace the heat exchanger (it should cover both parts and service – anyone who has a failing secondary heat exchanger should be sure they don’t let the HVAC company charge a cent) but a furnace isn’t really expected to last more than about 20 years, so prorating makes more sense.

In the case of a cracked main heat exchanger, you may be partly covered by the standard 20-year or lifetime warranty that Carrier offers on its heat exchangers, but for a cracked main heat exchanger, only the part is covered and you could be looking at several hundred dollars of labor to install it.

I know the cracked Carrier heat exchanger problem has made a lot of people unhappy about Carrier but in fact they are really one of the best furnace companies on the market, and I know several installers who won’t install anything else. I installed a Bryant furnace in my own home 13 years ago and it has never caused me any problems (Bryant and Carrier are both made by the same company.) The Carrier Infinity ICS furnace is probably the best furnace on the market – and won’t have the same cracked Carrier heat exchanger problem you’re experiencing.

Green Energy Efficient Homes articles cited

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