The system is driven by one pump, the left and right circuits have their own separate pressure check valve.
The rams have Hall sensors that are effectively limit switches that are triggered when the Rams are fully extended (or very close) - The system operates based on both switches being true to confirm roof up or down, but the trigger for the pump to auto run and repressure is based on one switch and timer. When you put the roof up, when the open limit switches are reached, the roof pump will continue to run (even with finger off button) until the pump electrical current reaches the point that is aligned to the system being fully pressurised.
My personal observation is that for me the roof sag is directly linked to strong sun on one side or the other during the day and that side will drop slightly overnight as it cools. I believe is the high temp either allows the fluid to flow past seals or it raises the pressure slightly and flows past the pressure valve. I made white plastic shields to give the rams sun protection and this largely stops the sag on our van. (Detail in link below inc. pictures)
We had a problem with our roof this time last year resulting in a replacement electro-hydraulic pump. Since then roof has never budged 1mm even after being up for days. This holiday we have noticed roof sinks on passenger side corner after one day. Drop roof 12 inches, put it back up and it’s...
vwcaliforniaclub.com