You can read these codes yourself, from the black box in right front corner of engine compartment. It's probably a particular sensor or one of the interior temp sensors with the tiny fans that get clogged. Last time for my 850, it was the passenger temp sensor (above the passenger grab handle), and you could only tell because the temp control for passenger side of cabin wasn't making much difference. Overall, whole system worked well, and you could hardly notice, unless your passenger wanted a much different temp than the driver. The lights don't flash for low freon.
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Mike Sullivan ('95 855T (88k), '98 V70XC (92k), '95 855 NA (135k). Past Volvo's: '85 744 (256k), '86 245 (165k), '86 245 (195k), '88 745 (208k), '91 745 (196k), '93 965 (147k) .