So I was raving about how a variable speed saved me so much money so a friend bought one , the problem is he can't keep it full unless at full speed, it only has one line coming into it that I believe controls 2 wall drains plumbed together then it goes to a cartridge filter out to heater then to a 3 way stuck in neutral, can air be the case at low and not high? Or are the two drains and the distance to much? Btw skimmer is on it's own pump with inground pool jet cleaners.