Shortening a cap tube does what to the head pressure?

[fixbear]

Depends how much you shorten it.  What you do when you shorten the tube is increase the feed to the evaporator, which theoretically will increase the head. However in real practice the condenser is built 20% oversize and you would not be able to see any difference unless you shortened the tube more than 20%. Usually 2 ft. even so, the ambient temp, air flow and condenser cleanliness would have more of a effect. Think of it this way, the cap tube is a fixed metering device, where as a TXV is a variable.. As head pressure rises with a cap tube , the flow also increases, which raises head pressure. Sounds like a vicious runaway, right. But ambient air, condenser actually is what will throttle it in. That’s why air flow and clean condensers are so important. Yet the most forgotten item on coolers. Makes for work security.