Original message
| gabrielnorbac
 |  "charge on freon 134a help"
, posted Sun 5 Oct 14:36  
I have a question I got everithing ready in my refrigerator charge freon but now the suction line get fozen my presion on charge line is on 10psi is that correct is a compresor 1/4 134a can someone tell me thg rigth charge on freon I thing thats the problem
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Replies:
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| Schock Therapy
| "Re(1):charge on freon 134a help" , posted Mon 6 Oct 00:07
A suction pressure of 10psi does not tell us enough. It all depends on the type of system you are dealing with, and the temperature of the evaporator etc.
Assuming you are charging a domestic refrigerator, with a capillary tube for a metering device, you are dealing with what is referred to as a "critical charge system". This means that the system requires precisely the correct amount of refrigerant to operate at maximum efficiency. The easiest way to charge such a system is to weigh in the exact factory charge as indicated on the appliance nameplate. If you don't have that information, then you should charge the system as follows:
Attach an accurate thermometer to the suction line a few inches away from the compressor. Charge the system until it starts cooling, and the box temperature starts coming down. Let the unit run, with nothing in it, until it is down near operating temperature. The system is now running in "minimum load" condition. At this point a properly charged cap tube system should be running around 10-15 deg F superheat. This ensures that there will be no liquid refrigerant flooding back to the compressor. (liquid doesn't compress well!)
What do I mean by 10 degrees of superheat? If you are using refrigeration gauges, you will likely have temperature markings for various refrigerants that correspond to the pressure markings. (If not you need a pressure-temperature chart for the refrigerant you are using.) For R134a you will see that 10psig corresponds to 12 deg. F. This is known as the Saturated Temperature. (Saturated means that the refrigerant exists in both liquid and vapor states) Therefore, if your suction line temperature measurement is 12 degrees, and your pressure is 10psi, then you can assume that there is saturated (liquid and vapor) refrigerant returning to the compressor. 0 degrees of superheat. This is bad: liquid will damage the compressor! (Frost on the suction line is an indication that liquid may still be boiling off.) You want to adjust your charge so that your temperature reading is 10 degrees above saturated temp. In this example 22 degrees. The refrigerant vapor will them be superheated 10 degrees above the point where it can turn into liquid at that pressure. If your superheat is too high, then the compressor will run hot, and eventually fail because it relies on cool refrigerant vapor to keep it cool.
So you see, there is a bit more to it than just charging to a certain pressure. sure you can use a more seat-of-the-pants method and get away with it, but you are better off doing it right!
It's only a shock if your not expecting it!
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| | gabrielnorbac
| "Re(2):charge on freon 134a help" , posted Mon 6 Oct 15:18
in the plate says 5 ozs but I know I put enouhg freon
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| | Schock Therapy
| "Re(3):charge on freon 134a help" , posted Mon 6 Oct 19:27
but did you put in too much? That was my point.....overcharging is as bad or worse than under charging.
It's only a shock if your not expecting it!
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| Jojo98
| "Re(1):charge on freon 134a help" , posted Sun 5 Oct 23:09
10 psi is at 7deg f. 134A suction pressure should be above 28psi to avoid freeze up. Locate manufacturers data plate on the fridge, it should give the exact charge for the appaliance.
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