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Old 07-15-2012, 11:25 PM   #1
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Frost on HVAC: Round 2!!


Hi all,

This evening I noticed a crackling noise coming from the intake vent, and downstairs in the laundry/HVAC room I found frost inside and on one of the pipes (Sorry, I don't know the names of the parts). I turned off the thermostat (AC was set to 78) to be safe. I went outside and noticed some frost on the insulated pipe that runs from the unit to the house. Even though it had just rained, I could tell it was frost as it was cold to the touch despite being 80 and humid out.

Some extra details:
Back in April we had frost on the inside HVAC system in the same spots - the pipe and inside where the air filter goes. That time, it was while the HEAT was on (we had a cold damp day). I had originally posted about it here: FROST on HVAC?
The cause was determined to be unclean air filters, in that while I regularly replace the filter in the unit, there had been 3 intake vents (one one each floor) that also had filters that hadn't been replaced since we moved in (by then it was 9 months). It was figured these were causing air flow restriction. Everything worked fine since, at least as frost is concerned.

Back in June the compressor in our AC unit outside broke. We were without AC for a couple weeks. It was replaced about 2 weeks ago after we brought our newborn home from the hospital. Its worked fine since...

Tonight I also noticed two strange things: Despite having turned off the AC from the thermostat and also made sure the "fan" option was not on, the large fan on the outside AC unit is still spinning. Also, inside the HVAC unit in the utility closet, I could hear a strange gurgling type noise. I filmed it but don't know if there is a way to post that here.

Photo of frost inside is attached, though its the same location as in the old thread from April. Also attached photos from outside, too.

I have emailed my contractor (house is just less than a year old) but thought I'd post here too!
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Old 07-16-2012, 07:06 AM   #2
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Frost on HVAC: Round 2!!


Quote:
Despite having turned off the AC from the thermostat and also made sure the "fan" option was not on, the large fan on the outside AC unit is still spinning. Also, inside the HVAC unit in the utility closet, I could hear a strange gurgling type noise.
Is the fan spinning at full speed, or is it turning slowly?

If it's at full speed, then you may have a contactor that's stuck, or faulty thermostat wiring (or a faulty thermostat). If that's the case, then the compressor is almost certainly running as well, and that will freeze up a system in minutes if the indoor blower isn't running. Something like this may or may not be covered under warranty - for example, if you find that ants have nested in the contactor and caused it to weld shut, that would certainly not be covered under warranty.

If it's not at full speed, then you have some sort of electrical problem in the outdoor unit (bad motor or capacitor, most likely).

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Old 07-16-2012, 09:03 AM   #3
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Frost on HVAC: Round 2!!


filter and squirrel cage rounds are clean,sounds like a fan speed problem.anytime the air across the evap (within the air handler/furnace) changes from HI the temperatures start to drop accordingly and the frost line starts on the insulated SUCTION line.it then travels out to the compressor and the humidity in the air is why the ice forms all the way out.so you basically have a refrigerator freezer situation.if it does it on a hot day and the house is warm could be a charge problem.note as the ice buids up in the air handler the air is restricted more and more and the ice really starts to build.you ight and could look down into the condenser out side an see the compressor totally covered in ice.to defrost shut the disconnect outside and put the stat to FAN ON only with no system OFF no cooling.that condenser fan runnng with no stat call need to see if the compressor is also on then you have a control problem.that thing running wild over night building ice no air must be solved...
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Old 07-17-2012, 10:40 AM   #4
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Frost on HVAC: Round 2!!


Apparently it was a bad thermostat (though only 11 months old).

We'll see how it goes
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