I have a 1984 Catalina 30. I purchased the boat last year and she came with a built in AC unit. I'm not sure of the brand but it is an older unit with three variable knob controls. One is for turning on the pump than compressor. The next is for temp. control and the third is fan speed. The AC has worked great until now. Last weekend, I left the unit on and when I returned on Sunday, it was warm in the cabin. I looked at the unit to find it frozen up. Is this condition due to it getting too cold in the cabin or is there something I need to check in the unit itself? Again, thanks for your help.