Hot gas defrost refrigeration valves are used to defrost the evaporator in low temp freezers.
These valves are installed in the discharge line of the condensing unit.
During normal operation hot refrigerant gas enters the condenser coil.
When defrost occurs, the valve opens and the hot gas enters the evaporator between the expansion valve and the distributor.
Separate refrigerant piping is necessary.
As the hot gas enters, the evaporator warms and defrost begins.
The valve is energized using a defrost time clock. The clock can be set for time of day and length of time, for each defrost cycle.
The valve is unenergized by one of two methods.
1. Time: The time clock's time limit returns the valve to its normal position.
2. Temperature: A temperature sensor mounted on the evaporator overrides any remaining defrost time.
What can go wrong?
The valve can fail to open or close correctly.
What to look for?
Touch the refrigerant pipes. The defrost piping should not be hot during the cooling cycle.
If the pipe is hot, then the valve is partially open. Chances are the internal piston is stuck.
Sometimes trash or debris causes the valve to stick.
Sometimes the piston is worn and does not easily slide within the valve body.
I first try cleaning the parts of the valve and the valve body. If the problem reoccurs, I replace it.
Why use hot gas defrost refrigeration valves?
Hot gas defrost more efficient.
Check out defrost controls for more information.
The above described system is very simple and often found on smaller commercial refrigeration systems.
Larger commercial and industrial equipment, using multiple evaporators, are of course more complex and specialized.
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