Thread: Indoor AC coil cabinet sweating?

Every once an a while I come across an indoor AC cabinet that is wet (sweating) all around (some units located in the attic and some in hall or garage closets). The temperature differential is usually good. How should this be noted in the inspection report? Thanks

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When i find sweating as you mention there is usually air leakage somewhere around the coil box or plenum.

rick

Originally Posted by Michael Vasquez

Every once an a while I come across an indoor AC cabinet that is wet (sweating) all around (some units located in the attic and some in hall or garage closets). The temperature differential is usually good. How should this be noted in the inspection report? Thanks

In cases I have seen the air flow is restricted because of a dirty condenser coil and it is either icing up or close to it or insulation is missing in the cabinet. It shouldn't be sweating. This is when you see mold/mildew build up. I have also seen it with a few closed off vents and all that air flow is trying to push out the remaining open ducts. You have to have balanced air flow.

Originally Posted by Michael Vasquez

(some units located in the attic and some in hall or garage closets)

Originally Posted by Ted Menelly

or insulation is missing in the cabinet. It shouldn't be sweating.

If the AHU is in a hall closet, that would be within the conditioned space, no sweating should be expected there.

If the AHU is in an attic or in a garage, in unconditioned space, many times there is enough humidity in the air and enough temperature difference to cause a high dew point at the surface of the cabinet.

I've seen - in new construction - units in a garage or attic, all sealed up, no air leakage, yet lots of sweating. These are brand new units with the insulation intact, no time yet for the insulation to have become wet or damaged.

One of the problems is the R-value of the insulation inside the cabinet may not be sufficient to keep the cabinet below the dew point under those hot and high humidity conditions.

Years ago (maybe 10 or so) in talking with one of the manufacturers they stated their units should not be installed in unconditioned space. When I called back later to get that in an e-mail or fax as they has said they would send me (but never did) I was told that their units could be installed in unconditioned space.

I don't know if it was just me or not, but I suspect the builder told their HVAC contractor who told the factory representative who told everyone at the factory that if they say that, they will no longer be selling any AHU in Florida (because they were all being installed in unconditioned garages). I think the idea of losing all of those sales resulted in a change in their position regarding installation in unconditioned spaces.

In my second call to them, they said that 'no we did not say our units *SHOULD NOT BE* installed in unconditioned space ... we said we *recommend* that our units be installed in conditioned space, ... but that *it is okay* to install our units in unconditioned space' ... yeah, right, I bet the first person I talked to was right.

If you see horizontally installed AHU in attics (unconditioned space) sweating along the bottom and only a couple of inches up the sides, that's a pretty good indication that the condensate pan in the unit overflow inside the unit and soaked the insulation on the bottom and the lower part of the side insulation, making it almost useless. When you see that, you will not see a secondary condensate drain line installed draining into the auxiliary drain pan - because the HVAC installer said 'I don't need to install a secondary condensate drain line to drain into the auxiliary pan, when the primary condensate pan overflow all of that is going to run out the seam in the AHU cabinet and drain down to the auxiliary pan anyway'.

Hey, HVAC tech ... why do you think the manufacturer installs that secondary condensate drain line?

Yeah, to avoid ruining the friggin' insulation in the AHU when it overflows!

Crimeny, those HVAC techs should have to pay to replace each and every single unit damaged by them not installing the secondary condensate drain line. If they were to pay for even one, they would likely never leave that secondary drain line off ever again.

Coils could be iced over. When I have found a condition like you described the coils have been iced over.

How should this be noted in the inspection report? Thanks

Report what you see. "The xxx unit was wet with condensation, have a xxx technician check it out"

Honestly, I cannot remember the last time I saw an upright with a secondary drain line. Just recently I see the cut off switches installed where the secondary drain line should be when I inspect some new homes.

As past discussion have went. What if the cut off switch stops working?

The water has no where to go but back down thru the unit and of course there is never a drain pan under them either.

Thanks for all the helpful feed back.