Sounds as if you were right at the low pressure cut-off point (25). If pressure was cycling 25-45, my guess is that the compressor was cycling on and off, since the pressure rises when the compressor is off. You need to measure the pressure with the compressor running steadily and the system stabilized by running a few minutes. Be sure that your pressure while compressor is running isn't stabilizing at 45+, as that is going to cause problems. If you added one can iof freon, I would expect your pressure went from 25 to around 35-38, and that will be fine for al normal climates.
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Mike Sullivan ('91 745 (171k), '93 965 (147k), '95 855T (60k), '98 V70XC (78k). Past Volvo's: '85 744 (256k), '86 245 (165k), '86 245 (195k), '88 745 (208k).