Spa water level drops when using manual vacuum

[teaching_texas]

We have a 26 year old pool. Last year we had some pool people come and redo the concrete around it. When they did this, they replaced some piping under the concrete. We weren't given instructions or manual for using the new equipment. We are trying to manually vacuum the pool (which we have done for years), but when we get suction in the vacuum line, the spa drains. When we can get the water back up in the spa, there is no suction for the vacuum.

We know there has to be some setting that we are missing. We have 2 skimmers, and we put a tennis ball in the one on the end to close the suction to that skimmer.

Attached is a photo of our pump setup. Any idea what we need to change to keep water in the spa and still have suction power in the vacuum?

 

[JasonLion]

There is a valve to the right of the pump, relatively near ground level, that controls what gets suction. When the handle points towards the house you should have suction at one of the pool and the spa, and when the handle points away from the house you should have suction at the other. You will need to experiment to figure out which is which. When that valve is in the pool position, there should be suction at both skimmers and the spa should hold it's level. Assuming that is true, you hook the vacuum up to one skimmer and block the other skimmer and you can vacuum.