pumping down a system

[nesh4220]

hi.
i happen to be a student learning HVAC/R trade..
would someone out there help me by noting down the actual procedures for pumping down a system.
that is, i want to take the ***** out of the system and charge the system again.. what would be the recommended steps.. HELP. thanks.
NESH 1

[james10]

Pumping down a system does not involve removing the refrigerant,by pumping down the system you are using the compressor to move the refrigerant into the high side of the system, this technique is normally used for service work e.g changing drier cores etc,
to remove refrigerant you need to use a recovery unit and receiver cylinders following local proceedures.
For small systems i would do the following
1,connect gauges to high side and low side ports(if available)
2,connect line from gauge manifold to suction side of recovery unit
3,weigh cylinder and note weight check cylinder details to be sure ther is enough room in the cylinder for the unit charge
4,connect gauge line from discharge side of recovery unit to receiver cylinder
5,purge lines
6,open valve on cylinder and allow pressures to equalise
7,turn on unit recover to -5psig(0psig if a leak on the system is suspected)
8, check recovered amount by weight
To recharge a system varies depending on refrigerant used and system type