NC joe
20-10-2007, 01:03 PM
Hello everyone,
i have never used a discussion forum before so please be patient as I figure out how to use this. i have posted this question before but I think in the wrong forum so here we go. I have a compressed air dryer that is shutting down on high refrigerent discharge temperature. This system is very simple as far as refrigeration circuits go. It is a 134A system.It is simply a compressor, condenser, then a cap tube to the evaperator out of the evaperator there is about a foot of suction line before the hot gas valve tees in. This hot gas valve is really nothing more than a suction pressure regulator. When this thing is under a normal load, I have about 35 degrees F superheat. Head pressure is at a normal pressure of about 165 psi, suction is stable at 28 psi no matter what load you throw at it which tells me the hot gas valve must be working well. in past experience with similar machines that are designed like this, I have observed that when the charge is low my head pressure usually drops while the temperature of the discharge refrigerent from the compressor climbs to higher than normal levels and superheat increases. Since my head pressure seems normal at lower loads and seems to climb as expected with increased ambient temperature I am thinking the cap tube must have blockage. even under an extreme ambient temp and extreme load on the evaperator the hot gas valve is still assisting the suction pressure. my theory is that I have enough refrigerent but since the cap tube is restricted I am not sending enough refrigerent into the evaporator so the hot gas valve(or suction pressure regulator as I like to call it) has to open and let some of the high side refrigerent in to keep the suction up. At the same time I still seem to have plenty of head pressure. I am working with someone who likes to add refrigerent no matter what the symptoms are and his answer to every problem is "Add more! It has to be low!" If this system were low wouldnt the result of the hot gas valve opening to assist the suction side pressure be that my head pressure would be low? Is there any good way to be absolutely sure whether or not my problem is cap tube blockage or low charge without evacuating the charge and weighing it? I like to do things based on facts and not just add refrigerant and change parts untill the thing starts working. Any help in understanding this better is much appreciated. Thanks in advance for any input.
Regards,
joe
i have never used a discussion forum before so please be patient as I figure out how to use this. i have posted this question before but I think in the wrong forum so here we go. I have a compressed air dryer that is shutting down on high refrigerent discharge temperature. This system is very simple as far as refrigeration circuits go. It is a 134A system.It is simply a compressor, condenser, then a cap tube to the evaperator out of the evaperator there is about a foot of suction line before the hot gas valve tees in. This hot gas valve is really nothing more than a suction pressure regulator. When this thing is under a normal load, I have about 35 degrees F superheat. Head pressure is at a normal pressure of about 165 psi, suction is stable at 28 psi no matter what load you throw at it which tells me the hot gas valve must be working well. in past experience with similar machines that are designed like this, I have observed that when the charge is low my head pressure usually drops while the temperature of the discharge refrigerent from the compressor climbs to higher than normal levels and superheat increases. Since my head pressure seems normal at lower loads and seems to climb as expected with increased ambient temperature I am thinking the cap tube must have blockage. even under an extreme ambient temp and extreme load on the evaperator the hot gas valve is still assisting the suction pressure. my theory is that I have enough refrigerent but since the cap tube is restricted I am not sending enough refrigerent into the evaporator so the hot gas valve(or suction pressure regulator as I like to call it) has to open and let some of the high side refrigerent in to keep the suction up. At the same time I still seem to have plenty of head pressure. I am working with someone who likes to add refrigerent no matter what the symptoms are and his answer to every problem is "Add more! It has to be low!" If this system were low wouldnt the result of the hot gas valve opening to assist the suction side pressure be that my head pressure would be low? Is there any good way to be absolutely sure whether or not my problem is cap tube blockage or low charge without evacuating the charge and weighing it? I like to do things based on facts and not just add refrigerant and change parts untill the thing starts working. Any help in understanding this better is much appreciated. Thanks in advance for any input.
Regards,
joe