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Waqas Ahmad
07-06-2009, 12:30 PM
Helo;

I am a new member in this forum. I am working in a manufacturing industry of Split air conditioners. Normally; the vaccum pumps are used for evacuating the nitrogen gas and for creating the vaccum for gas charging in the air conditioning units. I have encountered a problem during my 3.5 years service. We found oil in the tubes connecting with the Vaccum pump and the Air conditioning unit. It happened very first time. Can some one help me out how it happened because normally the pump evacuate the gas not the oil from the compressor.
Waiting;

Regards,

Waqas

brunstar
07-06-2009, 01:09 PM
when you are evacuating a system you need to ensure that you evacuate from a high point within the system to avoid this.
As you stated in your write up you said that you are using the vaccum pump to evacuate the nitrogen, what could have happened, if you do not let the nitrogen out of the system before connecting it to the vaccum pump you will push all of the oil out of your vaccum pump.
where are you evacuating the system from?
Try the highest point in the system and not the scherator valve terminal on the compressor if there is one there.

NH3LVR
07-06-2009, 01:19 PM
What you are seeing may be what is called "Backstreaming". When the Vacuum pump gets to a low enough level the flow changes from Viscous to Molecular.
At this point a small amount of oil will go leave the pump and go back up the connection line. In critical applications a device called a Foreline trap is used to prevent this.

Waqas Ahmad
08-06-2009, 07:02 AM
Many thanks to your replies. Its still confusing for me to understand. Let me explain to you again. Basically we are assembling split air conditioner. After completeing the brazing of the condenser with the compressor fitting, capillary tube and valves, we normally perform the leak test after injecting 150-175 psi nitrogen pressure in to the system for verifying the leaks from the points of brazing. After that the unit is sent to the Vaccum Loop. There are 12 stations and at a time 12 units can be vaccumed. There are two pipes coming out of the vacuum pump and both are connected to the the two valves of the unit through a coupler. The point is whether the oil seen is sucked from the compressor or it is of the vaccum pump because this situation is not so often. After vaccuming, we charge the R-22 Gas throug the charging machine.
Please give me some idea how we can control this situation. Would this oill effect the proper vaccuming of the unit?

icecube51
08-06-2009, 04:16 PM
do you use filter dryers between the pomp and unit connections. if so,it can be that the filters need to be replaced. if no,its like NH³LVR said, backstreaming.

Ice