A Note About System Charging

Eugene Silberstein 3

A got a call from a friend yesterday who was having problems getting a system back online after a repair was made. "Eugene, I've been on this system for a week and I have not been able to get this thing running." I asked a few questions and determined that the condenser subcooling was low and that the evaporator superheat was high. Both of these are indications that the system is undercharged, so I probed further.

"What type of metering device do you have?" A TXV.

"Is this the original TXV?" No, we just replaced the device.

"Exact replacement?" Yes.

"What is the delta-t across the evaporator coil?" 8 degrees.

"What else was done to the system?" We replaced the compressor on the system.

"Is this a packaged unit or a split system?" Packaged.

"Is the compressor an exact replacement?" No.

"How did you charge the system?" We weighed the charge in.

"You have an undercharged system."

Indeed the system was undercharged. A couple of quick notes:

1 - If you replace a compressor on a system, the internal volume of the new device may very well be different than the original compressor. You cannot go by the nameplate charge if such is the case. Pull out the gauges and thermometers and do it the old fashioned way.

2 - If the system is a split system, the nameplate charge may very well not be accurate, especially since the equipment manufacturers will have no idea how long your refrigerant lines will be.

3 - Also, the addition of liquid line driers, etc, also add to the amount of refrigerant in the system.

4 - When all else fails, use your superheat and subcooling calculations.

5 - Pressure enthalpy is your friend

6 - Hug your kids

Have a great day!

Empire_2

Just a safety REMINDER>>>>>>>>

Warning,....Do not set screws atop of the condenser while running. I did this and got projectile back at my head....OUCH!!!!!!!!!!! Never happened to me in 24 years of doing this, but Ya never know. Maby I should play the lottery???? Hummmmmmmmmmmmm.

Mike T. :-)

marco_5

charging

Eugene,

Have you posted a proper way to charge, and to check? I'm
sure i'm not the only rookie who would like to find out how the experts do it.

Marco

marco_5

charging

Eugene,

Have you posted a proper way to charge, and to check? I'm
sure i'm not the only rookie who would like to find out how the experts do it.

Marco

paul zeszotarski

meters

from what i have seen, the best way is always put on the gages and meters when charging a system. then you would know by the pressures and temps if the system is properly charged

Empire_2

As a general rule

If the manufacturers charging charts are availiable, use them. Other than that I will go by a slide rule which I got from Carrier corporation which gives TXV and fixed orifice proceedures. Temps, indoor and out should be taken, logged and compared to chart. Most important is the Wet Bulb temps which are very important to your final outcome. First and for most, all components must be cleaned "if necessary" before starting. Also, make sure to run equipment at least 10-15 min to allow the evap to start sweating which will give full load senarios. ALMOST FORGOT EUGENE,:-)...... If you have and know how to use P&E charts to plot system operation and the time,...That is the best way. I dont care what charts you have.

Mike T.