Scott I think a good study guide perhaps might be a copy of code check I don’t own one so I can not tell you where to get one.
- Service valve blocked or closed.
- After a restricted liquid line dryer.
- Bent or crimped refrigerant line.
- Blocked liquid line strainer.
- There was one unit designed many years ago that had the metering device in the condensing unit, upstream of the liquid line. The line would frost.
There are two service valve ports on a suction dryer. When the suction differential exceeds 10 psig (or mfg recommendations).
When the refrigerant circuit is worked on. Any dryers should be removed and replaced if necessary.
See Copeland refrigeration manual on “clean-up’s”.
Download any Mfg Installation manuals.
They are free.
If you use 10 LBS as your choice as a pressure and if we are talking medium temp R22 and you have a average suction pressure of 65 PSIG and a 10 lb drop would place you at 55 PSIG that is about where R22 starts to freeze condensate and you would see frost from the outlet of the dryer all the way to the compressor. I personally used the 3 to 5 PSI drop across the filter as a guide for change out
All are correct execpt # 1 a blocked or closed service valve gives you a pumped down system not frost
Note that most of the condensers these days come with a liquid line dryer already installed inside the unit. In that case another one should not be installed outside the condenser as it would restrict flow too much. Also, many do consider installation of a suction line dryer good practice … particulary after a compressor replacement as Dave mentioned.
A partly closed/blocked valve becomes a metering device, just like in the air handler. The restriction does “pump down” the liquid line. This reduced pressure lowers temp and WILL frost the line. Try it.
David I was just jerking your chain I know what you were refering to but your first statement did not state (partly closed) it stated closed.
However, when you pump down a unit and fully close the liquid line valve, often it will frost for a short time too. :-o
Now David you are splitting hairs here that would be called a defective valve and you would not get a pump down:D