AC/Heat - No low pressure warning with seacock closed???

[skibum]

I was on the boat for a few hours yesterday evening and it was a little chilly so I decided to turn the cabin heat on. After about 25 minutes I realized that it wasn't getting much warmer. I got up on deck and noticed that there wasn't any water coming out of the thru hull. I checked the seacock, and found that I had closed it the last time I was on the boat. I always close it, but I didn't remember doing it the last time I used the heat a few days ago. I had been worried about leaving it open while I was away from the boat. When I got in the ER, I noticed that the AC pump was pretty warm as well. I thought I had damaged something. I got back on deck and closed the hatch. The heat was still running, but I still had no water flowing. I went below and switched it to AC mode. In a minute or two, water started flowing. I switched it back to heat mode, and everything was fine. Good heat, good flow.

Now... Why didn't I get a low pressure error on the panel? I ran the AC for a few minutes with the seacock closed once right after I got the boat, and I got a "PS" (I think) warning on the panel. Shouldn't I have gotten an error last night?

Thanks,
Michael