I replaced a compressor on a practically new (about 2 years old) carrier heat pump recently. I found it strange (to me anyway) that this unit had 2 filter driers installed on the liquid line. It appeared that the one located between reversing valve and compressor was factory installed, but then there was a field installed filter drier just past the liquid access port. I checked others as we have around 80 units on this property and every one I checked had 2 liquid line driers.
I have always used a bi flow liquid line filter drier just past the liquid line access valve when one was not factory installed, never if one was already installed from the factory. Am I missing something.