I have a Carrier infinity system that is ~ 8 years old and has been fine until this year. it has been cleaned regularly. We have been through a BRUTAL cold snap the last 3-4 weeks. I will say we have gotten his cold previously but not for this length of time that I recall. To cut to the chase My concern / question is the amount of ice build up in the bottom pan I can't say for sure how thick it is but I would guess 1/4 to 1". It is below the coils. I am not sure if this is normal and if not how does one deice the pan? A bit more information follows.

The first problem noted was a pulsating noise when going into defrost. loud enough to be heard in the house.
The installer sent a service guy out. he checked the pressures and all seemed well. It went into defrost and the noise appeared.
He noted if he placed pressure on a front corner he could clearly feel the pulsing.
The unit had a fair amount of ice under and inside it with some frozen on the ground.
Raising the noisy corner seemed to help it a lot. It only made the noise one time after that and raising the same corner eliminated it again. I believe the unit may have been frozen the the stands and pan which was transmitting the noise.
A week or so went by and the unit threw a code 83 low pressure lock out. it was -10 or so.
Once it got back into the 20's I pulled the side panels and verified all was clean. The outermost drip holes were partially blocked so they were cleaned. There was a small amount of ice an some surface of the lower coils, not a lot or very thick, maybe an inch or so high in some areas. Again fairly small areas overall
using warm water and alcohol was able to get the lowest portion of the pan below the coils completely de iced and open.

The unit ran for about 2 hours and threw the code again. Temps have been as high as 25 with no change. We are running on backup electric heat and the installer is BURIED due to the unusual temps.

thanks for any input assistance