low charge or cap tube blockage?

[NC joe]

Hello everyone,

I have never used this before so hopefully I wont screw it up.
i have been messing with a refrigerated compressed air dryer. the system has 134A in it. I have about 30 to 35 degrees f superheat. My head pressure is about 165 psi suction is about 28 and stable no matter how much I load the evaporator. this dryer has a fan switch that turns the fans on at 175PSI and off at 105psi. I had thought that if my high superheat was due to a low charge I would see lower than normal head pressure with increased head temperature. I have the increased temp but not low head pressure. Even when i load the evaporator way beyond its design point the hot gas valve is still assisting the suction pressure (which explains my overheating problem) without droping the head pressure. To me this means I have plenty of regrigerant there is just not enough goin through the cap tube. I am obviously not a refrigeration expert but am I wrong in thinking that the cap tube must have blockage? How could I be sure if it is cap tube blockage or low charge without evacuating the dryer and weighing the charge? thanks in advance for any input.

[Bones74]

Hello everyone,

I have never used this before so hopefully I wont screw it up.
i have been messing with a refrigerated compressed air dryer. the system has 134A in it. I have about 30 to 35 degrees f superheat. My head pressure is about 165 psi suction is about 28 and stable no matter how much I load the evaporator. this dryer has a fan switch that turns the fans on at 175PSI and off at 105psi. I had thought that if my high superheat was due to a low charge I would see lower than normal head pressure with increased head temperature. I have the increased temp but not low head pressure. Even when i load the evaporator way beyond its design point the hot gas valve is still assisting the suction pressure (which explains my overheating problem) without droping the head pressure. To me this means I have plenty of regrigerant there is just not enough goin through the cap tube. I am obviously not a refrigeration expert but am I wrong in thinking that the cap tube must have blockage? How could I be sure if it is cap tube blockage or low charge without evacuating the dryer and weighing the charge? thanks in advance for any input.
Interesting. Well here is the bad news first. It's probably restricted and you over charged it. Probaby wax or moisture in the inlet of the cap tube. The pressure that you see is the refrigerant backing up inside the condensor:eek: Rule of thumb if you suspect a restriction, Put only half the name plate charge in the unit and if the pressures stay the same, replace the cap tube. I would change it and the filter, put in fresh gas and test it from there. Just a thought.:D

[Peter_1]

The hotgass bypass valve only tries to maintain a suction temperature above the freezing point of water.
This valve doesn't know if there's enough refrigerant in the system orr if the evaporator is heavy loaded.
Reclaim the gas, remove drier, blow through the caps in opposite direction, replace filter drier, vacuum the system the proper way and refill.

[Frudge it]

Hi NCJoe ,
I reckon the 2 previous posts to this on have your problem(s) nailed nicely - But I do want to add a fine point with the cap tube.Make sure the cap tube entry is nice & straight on reduction from 1/4 " & ensure that the tube where its been cut has been restored to original diameter by removing internal ridging at the original cut point.A fine set of gas tip cleaners for oxy / acetylene does wonders here , in conjuction with the both ways dry nitro blowout.
Cheers