The discharge service valve is constructed similarly to the suction valve and is primarily used to check discharge pressure and determine the condensing temperature.
Service Valve Positions:
Back Seated Position: The normal operating position where full flow occurs from the cylinders into the discharge line towards the condenser. The gauge port is closed.
Cracked/Mid-Seated Position: The valve stem is turned slightly (half a turn to one turn), allowing access to system pressure through the gauge port.
Front Seated Position: The valve is fully turned in (clockwise), isolating the discharge line from the compressor. Important: The compressor should never be operated with the discharge valve in the front seated position, as this can cause damage.
Isolating the Compressor:
To isolate the compressor for maintenance tasks like valve plate replacement, crankcase oil change, or compressor replacement, the discharge service valve is front seated.
This allows the discharge line to be isolated, and the remaining discharge gas can be purged from the compressor body.
Both the discharge and suction service valves are front seated to fully isolate the compressor.
Compressor Replacement Procedure:
After isolating the compressor, the service valves are unbolted from the compressor body, allowing the compressor to be removed.
When installing a new compressor, it is recommended to use new gaskets under the valve flanges to prevent leaks.
Evacuation and Dehydration:
A vacuum pump is used to evacuate and dehydrate the service valves and the new compressor body.
Since the system remains isolated, the refrigerant stays in the system, making the repair straightforward.
Final Steps:
After evacuation, the service valve stems are backed out to either the mid or back seated position.
Once the valves are back seated, the compressor can be started.
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