I asked some questions here and got some great advice about my Carrier Infinity system (3T and 4T Performance Series 2 Stage Heat Pumps / Infinity Air Handlers / Infinity Controls). Has been working absolutely fantastic. Heating and cooling bills improved and house much more comfortable. The duct work changes seem to be working well, as are the Aprilairre filters. Static pressue quite good!

But we've got a strange thing happening. Company not sure what is happening. Early one morning, with temps around freezing outside, the 3T unit started blaring VERY loud. Might be defrost cycle, but seemed quite a bit louder to me. Anyway, it stayed in that mode for 30+ minutes. Company said to turn it off, which we did, and repair guy, who came about 2 hours later, could not make it happen again.

The second time it happened the blaring did not seem as loud. Almost same situation, early morning, temps around freezing. Repair guy had asked us, if it happened again, to check some things, so we looked at the infinity control which said that defrost was NOT on. Fan was running on outdoor unit, and line was cool. Lots of dripping water around outside unit. We turned off the unit and waited about 15 minutes. Turned it back on. Within 20 minutes it was blaring again. Still no defrost notification on the control and same conditions at outdoor unit. I turned it off until nighttime and it has not recurred. Temps have been warmer since then.

Repair guy said it sounded strange, and thought it might not be the defrost board or sensor, but might be "compressor bypass." He was going to do some research. Wife is worried this is causing excessive wear and tear, not to mention using a lot of electricity. We're worried it will happen when we're not home and last all day.

He is coming tomorrow morning. Anyone have any idea what could be causing this?