The question was what causes the pressure, it can only increase in a confined space, if refrigerant is added but the same amount of refrigerant is added to a larger area it results in less pressure. The question is too vague; it should be what causes higher than design pressures in a refrigeration system.
[QUOTE]Originally posted by dexman TXV will override line size [/QUOTE
i have to disagree with this. to some extent maybe but if the suction line is to small you will loose btu. even thow the txv will maintain a set superheat it can not control the lose of btu in the suction line if it is to small or to long this is why it is so important to install the proper size line set. two small a liquid line will also affect the operation of the system and the txv can not control that either. if you run a 1/4 in liquid line and calls for 3/8 you head will be high and you more then likely will not stack up enough liquid for the txv to work properly. the size of the line set is just as important as the metering devise