Expansion valves can be the reason for lower than normal suction pressure.
They can also provide you evidence of another problem in a commercial refrigeration system.
Before tearing into an innocent expansion valve, listen!!! Do you hear a hissing noise coming from the valve body?
Notice any frost or ice?
Chances are it isn't the valve at all. The system can be low on refrigerant. Check the sight glass.
Sight glass flashing? There's the problem. Low refrigerant.
What's that you say? The sight glass is clear? But the valve is still hissing?
Is there a filter-drier between the sight glass and the valve? Guarantee you it's stopped up, restricting the flow.
Change it out.
But wait! The valve is not hissing but you still see frost or ice?
Sight glass clear?
Low suction pressure?
Now is the time to suspect the valve.
But is it really the valve? Chances are the valve is OK.
Only one way to really know! Disassemble it.
I'll bet you'll find a very fine white dusty material inside.
Or you may find some small pieces of copper or debris.
The dusty material is from a deteriorating filter-drier core. You must replace the filter-drier.
The copper shavings and debris are from the original installation.
Clean the valve and reassemble. Now it should run normal low side pressures.
Working on commercial freezers?
In addition to the above, you may have moisture in the system.
Moisture will eventually form ice inside the valve restricting or stopping refrigerant flow.
Remove the moisture by changing filter-driers as needed.
The moisture indicator on the sight glass will let you know when the system is free.
One more idea!!! Has the case always had a lower than normal suction pressure?
You may have the wrong valve or cage assembly installed. Seen it many times.
Saw it once on a system that had been working for years. Or should I say had been working at reduced capacity for years!!!
Boy, was the owner happy.
Don't forget the obvious, simple things!!!
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