jimg.allentown
Well-known Member
- Location
- Southeastern PA
After I read quite a few of these replaies, I have a few things to say.
Any moisture in the system is boiled out at high vacuum. That moisture is exhausted into the air, not the oil. The oil is mostly for the pump lubrication and internal sealing. The only time oil really comes into play is in a diffusion pump. That type of pump will only be found in high end analytical machines like a mass spectrometer.
There are mainly two "contaminents" that will adversely affect a refrigeration system. Air, which is a non-condensible gas (in terms of refrigeration) and moisture. Moisture can freeze in the metering device, which is the main reason for removing it. Secondarily is the possibility of corrosion.
Given all of this, it is not critical that every trace of moisture be removed. That is why there is a dessicant in the system.
Oil. Is important that you use the correct oil. The typical mineral based refrigeration oil used with R-12 systems is not compatible with R-134a. You need to use an ester-based oil. The oil in the system somewhat "blends" with the refrigerant as it travels through the system. The function of this is to provide proper lubrication for the compressor. It has been determined that oils used with R-12 do not blend and travel with the R-134a.
There is really no reason that the original R-12 comperssor should have been changed to convert to R-134a unless the compreeor was worn or failing. There is no physical difference in the compressors.
Leaks. The molecules of the R-134a refrigerant are smaller than the molecules of R-12. As such, the R-134a systems use barrier hoses. Many times just replacing the hoses with the correct type will eliminate small leaks.
In general, most HVAC applications are fine with a rough vacuum of around <400 microns. Most commonly available vacuum pumps will achieve this. The electric pumps tend to achieve a deeper vacuum (around 100-200 micron) than the air powered ones. Either should be sufficient for most refrigeration work.
There. I said my piece.
Any moisture in the system is boiled out at high vacuum. That moisture is exhausted into the air, not the oil. The oil is mostly for the pump lubrication and internal sealing. The only time oil really comes into play is in a diffusion pump. That type of pump will only be found in high end analytical machines like a mass spectrometer.
There are mainly two "contaminents" that will adversely affect a refrigeration system. Air, which is a non-condensible gas (in terms of refrigeration) and moisture. Moisture can freeze in the metering device, which is the main reason for removing it. Secondarily is the possibility of corrosion.
Given all of this, it is not critical that every trace of moisture be removed. That is why there is a dessicant in the system.
Oil. Is important that you use the correct oil. The typical mineral based refrigeration oil used with R-12 systems is not compatible with R-134a. You need to use an ester-based oil. The oil in the system somewhat "blends" with the refrigerant as it travels through the system. The function of this is to provide proper lubrication for the compressor. It has been determined that oils used with R-12 do not blend and travel with the R-134a.
There is really no reason that the original R-12 comperssor should have been changed to convert to R-134a unless the compreeor was worn or failing. There is no physical difference in the compressors.
Leaks. The molecules of the R-134a refrigerant are smaller than the molecules of R-12. As such, the R-134a systems use barrier hoses. Many times just replacing the hoses with the correct type will eliminate small leaks.
In general, most HVAC applications are fine with a rough vacuum of around <400 microns. Most commonly available vacuum pumps will achieve this. The electric pumps tend to achieve a deeper vacuum (around 100-200 micron) than the air powered ones. Either should be sufficient for most refrigeration work.
There. I said my piece.
pressure testing with shop Air usually does this.