What caused these burn marks?

Burn Marks on Air Handler

Phoenix Arizona suburb. House was construction complete about 6 months ago.

The tape and insulating foam around the bigger tube was cut. I assume the AC tech that came out to investigate the bad fish smell (see below) did the cutting, but I don't know for certain.

(Un?) Related Info:

Bad Fish Smell

A couple weeks/months after moving in we would noticed a strong body odor / fish smell in one area of the house, but nowhere else. It was sporadic. Sometimes we could smell it every night for a few days and sometimes we wouldn't smell it for a week or two. When it was there it would smell that way for hours. We usually only smelled it after dark. I had a theory that it was moisture making mold a day or so after rain, but it wasn't consistent. I replaced the air filters. No change. Google said it could be burning plastic and to call a pro. I called the builder and they sent an AC tech to investigate. The AC tech said they found nothing. We did smell it after they investigated, but we haven't smelled it in weeks/months. Maybe the heater was kicking on and making the smell and it hasn't kicked on since spring, so that's why we don't smell it anymore? Except, I don't think it was cold enough to kick on the heater.

Burning Plastic Smell

Occasionally we smelled a strong burning plastic smell. The odor was in the kitchen and every time we smelled it the gas stove was on, but we did not smell it every time the stove was on. I looked all around the stove and saw nothing abnormal. I couldn't pin the smell to the stove either. My wife thinks it was a specific pot. That pot never made the smell before we moved into this house and I was unable to replicate using that pot. We haven't smelled this odor in weeks/months.

  • 1
    Looks like you got yourself a badly build house. I'm sorry mate.
    – Mast
    Aug 18, 2019 at 9:05
  • Fish smell could be from overheating electrical parts. Is your stove gas or electric? It might be good to have an electrician check on it. If you could reproduce the smell, it would be a simple matter to look around with a thermal camera, but even otherwise they can open junction boxes and look around for signs of overheating.
    – jpa
    Aug 18, 2019 at 12:59
  • 1
    Could also be the heating up on your appliances when you’re cooking as you get your first few uses with them. Our stove had a burn in period in the manual of 3 hrs at like 300°. Aug 18, 2019 at 13:06
  • 2
    About the fish odor that depends on time of day.. perhaps it depends on which way the wind blows, which can vary with night-day cycle: 1, 2. Could be a small rodent that died somewhere near.
    – user
    Aug 18, 2019 at 14:12
  • Can the scorch marks be wiped off with e.g. a damp sponge? If they're wiped off, do they come back? Aug 19, 2019 at 4:10

1 Answer 1


The burn marks on the air conditioner air handler are from the torch the installer used to solder the copper pipes to the unit. The pipes then go the compressor located outside the unit.

Most installers can do this job without scorching the unit.


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