I have a Carrier Infinity heat pump that is about 6 years old, and it is not defrosting. We've had technicians out a few times, and yesterday we though he fixed it, but it's frosting again this AM. The best I can recall, these are the steps they have taken on each visit:
1. Check pressures and recharge. Tiny leak found and fixed.
2. Clean indoor portion of the unit (?) and re-check charge which was OK
May have been a visit between these two, but can't recall for sure.
3. Replaced temperature sensor. Yesterday he told me that he could force the defrost board to work manually after the sensor was replaced, but not before. Previous guys seemed to indicate they could force the defrost mode.
4. (yesterday) Re-check everything again. I didn't follow everything completed, by he said it went into "second cycle" and the charge almost non-existent, so he recharged. And honestly, he seemed surprised by that finding. He kind of insinuated that maybe the "second cycle" thing was not done properly at install (same company). We rejoiced because we thought we found the culprit, but it was frosty again this morning.
He mentioned replacing the board on visit #3, but noted that it was quite expensive, so we want to avoid that if possible, obviously.
One other thing, I remember hearing a "burst of steam" type of sound previously when it would defrost. But haven't heard that since this problem started. Nor have I heard it during any of their tests.
Yesterday, I kind of encouraged him to look at the control panel to see if there were any settings to be adjusted, but he didn't think that was necessary.
This started during the first cold snap of the year (around October). Prior to that it was working fine as far as I could tell.
So .... when I call them back, what kind of questions should I be asking and/or tests should they be running?