Filter driers often tell you when they are restricted.
If a liquid line drier becomes severely restricted it begins to actually meter refrigerant.
What happens when the expansion valve meters liquid refrigerant?
The refrigerant cools the evaporator.
The same effect occurs within a clogged drier. The drier becomes cold.
The downstream liquid line feels cooler. Often the drier body and the liquid line sweat or even form frost.
You'll note that I described the above as "severely restricted."
The drier can be partially restricted and the temperature difference very slight.
The more restricted, the greater the temperature difference.
However, there is an exception.
I have seen filters sweating, only to discover the drier was not restricted.
What was the cause?
Low refrigerant charge!
There was not enough refrigerant in the system to force the refrigerant through the drier core.
Once again the drier was partially metering the refrigerant.
Before automatically replacing a cool drier, check the sight glass. If the glass is flashing it's probably not the drier.
Want to know how to gauge the degree of restriction?
It's very sophisticated and takes years of training.
Making a seal with your finger, blow on the drier inlet. If the drier is fine, the amount of pressure is very slight.
If restricted you can't blow much, if any, air through the drier.
Remember to make a seal with your finger, the drier can contain some nasty stuff.
Ok, you got me.
So much for sophistication and training!
I admit it looks strange when I place a filter to my mouth an begin blowing!
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