Filter driers eventually wear out.
How do you know?
Look for the signals!
Many times, expansion valves and solenoid valves begin to fail for no apparent reason.
The expansion valve stops metering enough refrigerant. The suction pressure is lower and the superheat increases.
The evaporator is starved and the product temperature rises in the case.
Sometimes the solenoid valve will refuse to open or close or just stick partially open.
Your first reaction is to replace the valve.
And it works!
With the new valve installed, the problem disappears.
For a while!
Then it reoccurs, the same problem again.
That's what happened to me.
I replaced a liquid solenoid valve on a pump down system, that refused to close.
After installing the new valve, I repeatedly tested the control circuit.
If was working great.
A few weeks later I was back. The same valve refused to close.
Now my suspicions arose.
I decided to disassemble the valve for inspection.
What did I find?
I found a very fine, yellow-white powder, coating the interior of the valve.
Just enough powder to cause the valve to stick.
I knew what was going on. There was only one source, the filter drier.
The drier was old.
After removing it, I lightly tapped the body and watched dust fall out.
Years of refrigerant flow had gradually caused the core to deteriorate. Core material was being released into the refrigeration system.
This core material eventually clogged the solenoid valve and caused it to malfunction.
After replacing the drier and cleaning the solenoid valve interior, I restarted the system.
End of problem!
Now I always disassemble a valve and inspect the interior, before replacing it.
The drier core was sending signals.
I just had to read them!
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