Was over at friend's place yesterday and after about two hours the swamp cooler was getting down to 70 and a bit chilly so he turned it off and the left the room. When he came back he said he had to go shut the exhausting window as without the fan the hot air from outside blows back in.

Being somewhat lazy, I began thinking of options. A flap on the exhaust window with a light spring return so the fan-pressure kept it open when on.

Then the thought struck, what about a pump with variable speed? Or a waste-gate valve on the pump outlet to control the amount of water available for cooling. The variable waste-gate valve might be easier to find/make than a controllable pump. Maybe just s simple clamp on the pump outlet to restrict flow. The pump is not positive displacement so being backed up will not harm anything.

Anyone been down this road?

Other thoughts on controlling temps other than fan speed Low/High and pump on/off such that the fan can stay running, thus, the exhaust window can be left open?

Dave