Hi All. I have an ABTE1060 Trane Absorber with a 3 stage solution pump. I've always maintained a 10 degree differential across the evaporator but this season can only get 6 to 7. Nothing has really changed from last season. Tubes are clean, chemical tests came back fine, PD's across both bundles are fine, tower temp is between 85 and 90. I'm maintaining 60 - 62% strong solution concentration level as well. My question is, (and I've included a jpeg) there are 2 hand valves just under the motor of the pump. They are on the line from the pump to the economizers. One is an 1 1/2" and the other 3/4". Does anyone know what the position of these should be while up and running? They are both wide open. They look like they are manual bypasses for the economizers. Not really sure as I have never checked them before now. They may have been opened by someone who is no longer an employee here. I tried briefly closing the larger valve and the pump started making a noise similar to cavitation but there is plenty of solution in the glasses. Don't think it's that. Any input would be greatly appreciated.