Accurate Reason for Strange Smell from Forced Hot Air?

Since this past Saturday I’ve been smelling a strange smell from my forced hot air. It smells like burnt toast at certain times, but it’s hard to really describe. It does not smell like heating oil. It is not constant, and seems to be stronger if the system has been off for a few hours. It does not smell like it does when the system is first turned on for the season. None of my carbon monoxide detectors have been triggered.

I purchased the house 8 years ago and the furnace was replaced a few years before that. I would say it is just under, or right at, 10 years old. I also have central AC, which is probably as old as the house (built in ‘94/‘95).

I called a local company who I have used in the past. They guy came out and performed what seemed like a pretty thorough inspection. Of course, it didn’t smell when he was there. I also asked him to do the annual service. He took a number of readings, which I really don’t understand and also inspected the heat exchanger for cracks. He was not able to find anything wrong other than some rusting on the heat exchanger, which he recommended we just keep an eye on each year.

Since he couldn’t find anything wrong, his thought was that a leak in the A coil for the AC was dripping onto the heat exchanger and then causing the smell. He couldn’t confirm this though, since he does not primarily work on ACs (the company does, but it is large, so they just have specialties). He said we would likely have to replace the whole AC unit because parts for the type of coolant it uses are no longer available (I can’t remember what the R# was he said).

He did recommend some additional cleaning, but said it would not help with the smell. Also, the parts in the pictures he showed me did not really look dirty.

I don’t know much about HVAC. Does this scenario sound correct to anyone? I can’t find anything by googling. Is there anything I can do to confirm this is the issue without paying someone else to come out and look at it? I do not want replace the whole AC unit if I do not need to replace it.

Sorry for the lengthy post.

submitted by /u/HP_Wilson
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