FRONT SEATED

If the valve is front seated (stem set all the way to the front), the discharge line (or suction line with the suction service valve) is closed off.

As such, the connection between the compressor and condenser is shut off with the front-seated discharge service valve and the evaporator/compressor connection is shut off with the front-seated suction service valve.

Extreme care should be taken when front seating the discharge service valve with the compressor running because excessively high pressures will build up. When the compressor is running, front seating the discharge service valve should only be performed by an experienced, well-qualified technician for closed-loop capacity checks.

With the compressor off, both service valves can be front seated to isolate the compressor from the rest of the system. The purpose of isolating the system is for maintenance or replacement of the compressor. As such, the service valves allow relatively easy replacement of compressors. The only refrigerant lost is that between the service valves and only the new compressor has to be evacuated.