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Photograph of rust and leakage inside of an air conditioner Leaky, Moldy or Wet Air Handler FAQs

Q&A on Leaks & Mold Problems in HVAC Blower Compartments & Ducts

  • POST a QUESTION or COMMENT about leaks in air conditioner or heat pump or furnace air handlers and how to test HVAC systems for mold contamination

Air handler blower unit leaks & mold hazard FAQs.

This air conditioning repair article series discusses the problem of A/C condensate leaks into air conditioning system air handler units, blower units, or AHU's, (also called fan coil units).

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Air Handler Blower Leaks, Rust, Mold Q&A

Photo of water stains, rust, and possible insulation in air conditioner air handler fiberglass insulation (C) Daniel Fr4iedmanThese questions & answers about Air Conditioner Air Handler Rust, Condensate Leaks, Wet Insulation, & Mold Hazards were posted originally

at BLOWER LEAKS, RUST & MOLD - be sure to check out the diagnostic advice given there.

Photo: our red arrow points to mold-contaminated fiberglass insulation lining the bottom of a horizontal HVAC air handler in a building attic.

Notice the leak stains atop the foil facing.

Mold contamination in fiberglass insulation

What is the optimal moisture reading percentage for the fiber glass insulation in the air handler and inside the hvac unit all together. Ty. Have existing mold and need to know if insulation must be changed - On 2018-02-21 by Nicole-

Reply by (mod)

Nicole,

Because it's often impossible to see, with the naked eye, mold contamination in fiberglass insulation, if insulation has then actually wet and or if it is indeed visibly moldy on the surface or smells moldy, it should be replaced.

Beyond that point, making a specific moisture measurement, for example confirming that the moisture is below 18% - the critical threshold for mold growth - might be useful but it is absolutely not reliable if the results are negative.

By that I mean if you find high moisture and insulation at least raise a question of mold contamination or the invitation to mold growth. I just said that would be above 18%. However the absence of moisture is not proof that the installation has never been wet nor that it is mold free.

His reasoning I would look more generally at the conditions in the air handler for signs of leaks or soaked insulation.

If you're going to go to the trouble of fixing a problem like that make sure you find an address the water source as well. I'm less concerned about superficial wetting on fiberglass insulating panels that were coated with a waterproof surface.

See FIBERGLASS INSULATION MOLD


Sickening smell when I switch our furnace from heat mode to cooling mode

I have a problem with a sweet sickening smell when I switch from the heater to AC. I have severe allergies and asthma and an unknown couch that cannot be diagnosed.

I need some help in what to do. If the AC ONLY runs, you do not smell it.

However, if you have a cold morning and you turn on the heater and then have a hot afternoon and turn on AC, you get that sweet smell that makes me sick! I have had to tech guys out and they both have "cleaned" the coils, but it still stinks. I am running out of options and I am desperate for a fix! - On 2015-12-12 by Paula-

Reply by (mod) -

I don't have enough information to offer a useful diagnosis, Paula. I'm guessing you're talking about a heat pump that can be switched between heating and cooling mode.

If so, the ductwork, fan, and all air handling components are the same in the two modes. What's different is whether or not the aux heaters run or whether the heat pump runs in cooling mode or heating mode.

A more thorough on-site inspection of not just the HVAC system but possible odor sources is needed.

Moldy insulation was making our building air smell and made me sick

@Paula,
I would check for mold I had the same problem than turned to musty smell. Each time I turned on heat and or air made worse. I too have allergies and mold has made me sick. It may be where you cannot are or under insulation. Hope that helps a bit! Gl.


I need help diagnosing and fixing mold in my A/C cold air ducts

I have mold in my ac cold air trunk and all ducts. I want an independent evaluation of the root cause of this problem and not have to rely on my AC contractor. In my mind, this would be somebody who has no financial interested in duct cleaning, or remediation equipment or repairs. - On 2015-06-27 by Mike

...

Mike, did anyone answer your question? My husband and I are interested in the same thing - On 2015-08-26 by Anonymous

Reply by (mod) - See these Moldy Duct Work Diagnosis Guides

Mike and Anon,

These articles should help you out; let me know if you have specific questions.

See these articles that discuss causes & remedies & tests for mold contamination in HVAC ductwork. Through them you'll find more reading suggested at the ARTICLE INDEX.

AIRBORNE PARTICLE & MOLD LEVELS in DUCTWORK 

BLOWER LEAKS, RUST & MOLD 

WHY DOES MOLD GROW in INSULATION? 

What's the probability that mold is in my ductwork if we found mold in the air handler?

Filters in air handler at my wifes work had not been changed in around 4+ years,air flow got reduced and when handler was opened mold was found on both filters,the guy that removed the filters said they weighed about 2 pounds each had so much mold on them. After they were replaced they turned on the fan and said needed to blow the stuff out.

Wife told them she was allergic to mold and would be sick and she is! The general manager said he looked in the air handler and said no mold was in it.

What is the probability that there is mold still in the handler and duct work? On 2015-06-02 by Darrell

Reply by (mod) -

Darrell

Probability of detectable mold = 1.

Probability of a dangerous or harmful mold contamination: we really can't say, nor can we imagine that the 2 pound weight was really all mold.

But certainly the sudden increase in air velocity of removing dirty clogged filters would be expected to blow whatever is in the duct system and air handler and blower fan itself out onto the building occupants.

I'm doubtful that either the HVAC tech or the manager were actually qualified to make an evaluation of mold hazards.

...

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