Help! New a/C Tech Having Charge Probs?

Overcharging is pretty common for a lot of techs. They like to read the gauge and keep dumping gas in until they get 62 psi suction. Beer can cold is still a bit cool for the suction line. It should stay pretty consistent with a txv, but will change a bit with an orifice (piston). The rule of thumb I learned when I started is 10 degrees superheat, 20 degrees temp drop across evaporator, 30 degrees temp pickup across condenser. This assumes that evap and cond coils are reasonably clean. Anymore, I do not use the gauges unless there's a problem. If you are getting airflow across both coils, your suction should be cool, but not ice cold....your liquid line should be ambient, or just a bit warm....you should feel heat coming from the condenser, and get a good temp drop across the evap. In many cases, there are a lot of variables (installation) which change the exact pressures and temps that the system will run at. I guess the bottom line is that you have to have some superheat, or you will kill the compressor, either sooner or later. Confirm that airflow, do not settle for less than 10 degrees superheat, 15 or even 20 is better yet. It can be confusing at first, but try to imagine what the refrigerant is doing inside the pipe. If you understand the refrigeration process, it will get easier with practice. Hope this helps....Best of luck to you. 20 years HVAC tech.

1. Car A/C evaporator Help !!!!!!!!!!!!!!!!!!?

There is no reliable way to repair a pin hole in an evaporator. basically any real fix would require evaporator removal, and with as much work as is required to get an evaporator out in most cars, attempting a repair is not worth the hassle of possibly having to do it all over again. just replace it

2. How do I clean an evaporator coil in my furnace?

I clean mine once a year firstly by vacuuming it with the hose attachment with the brush nozzle on the end. Then I wipe it down with a damp cloth.. Make sure you disconnect the power from it before you do this, of course..

3. Does a rotary evaporator need a draft chamber and a vacuum pump?

I've never seen a rotary evaporator without a vacuum pump. They generally use a water bath and are severely limited in the temperature they can achieve due to that. It is also much easier to adjust the pressure to get the desired evaporation rate than to try that by changing the temperature. And in your case, a rotary evaporator without a vacuum pump would have to be an open system, so DCM could easily get into the atmosphere.Rotary evaporators are a closed system, and you would generally notice any big leaks because you wo not be able to achieve a good vacuum. For common solvents I see no huge advantage in putting them into a fume hood, and they often are not because the space in the hood is rather precious. But DCM is potentially carcinogenic, so I can certainly see where your advisor is coming from and I would also prefer to put it into a fume hood. You also handle the open flasks when attaching and detaching your sample and the solvent waste to the rotary evaporator, doing that under a fume hood is a good idea

4. Will my air conditioner still work properly if I let the ice on the evaporator coils melt?

After it thaws it will work for a while til it freezes over again. You need a repairman

5. How to fix the freezer compartment/ evaporator fan of my fridge?

When you manually defrost you should let it melt or boil a pan of water to make it melt faster. My friend used a butter knife one time and we heard a hiss and it was the refrigerant leaking out. Sounds like you need a new refrigerator

6. Phase of refrigerant when entering evaporator?

Assuming that your system is a normal refrigerant system, the refrigerant exists in the evaporator under saturated conditions, because the high pressure, hot refrigerant goes through an expansion valve, and "flashes" at the lower pressure. This means that there is excess heat in the high pressure refrigerant when it experiences lower pressure conditions, and the refrigerant boils and loses heat and temperature until the refrigerant reaches the temperature that corresponds to the new pressure that it is seeing, according to the Antoine equation. The only way to experience several degrees of subcooling involves some type of heat transfer to the environment immediately after the expansion valve. This is not going to happen, for at least two reasons. No chemical engineer (my background) would try to design a process to do this because extraneous (and expensive) equipment would be involved, and the heat transfer to the environment immediately downstream of the expansion valve would have to be very rapid (big heat exchanger area involved). There is a very high probability that your information has an error in it, so it is very unlikely that you need to worry about the 7 degrees of subcooling mentioned in your problem statement. In the unlikely event that your process actually does deal with subcooled refrigerant, you would need to post a process drawing so others on this site could determine how the stated process conditions are being achieved

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