Evacuation Levels Prior To Refrigerant Charge

[eciguy]

Any air conditioner manufacturing engineers out there? What micron level do you evacuate your units to prior to refrigerant charge in order to "boil off" the moisture? We've polled many of our clients and would like to broaden the scope of our research for our VacuCharge system:

http://www.ecicomplete.com/vacucharge.html

So far it appears that the average is 200-400 microns.

 

[hockeyman]

As a mechanical Engineer for a large air conditioning manuf.for my test purposes in the lab I make sure my techs take the vacuum down to 50 microns and let it hold for 30 minutes ( these are new systems so the only oil in system is in compressor )but I know on the production floor they are not so thorough,they are on a assembly line there instrumentation is old and uncalibtated, I'm afraid to actually check the vacuum readings,if I do the V.P. of production along with Q.C. and tell me to get off the floor
I'm interfering in there tests so I know foe a fact it's going to be a warrantee issue in a little while.

 

[MintJulep]

You need to be careful where the vacuum level is measured. It is very common to put the vacuum gauge or sensor right on the vacuum pump suction port. This produces an artificially low reading that is not representative of the vacuum in the system.

It is preferred to take the vacuum reading from an access directly into the system, as far from the pump's connection as possible.

Age old battle, as noted by hockeyman. Engineering wants the lowest vacuum possible. Production wants a much higher level.

Minimum pressure reached is not the only thing to consider. Time at that level with the pump connected and running is also important. Vacuum decay with the pump isolated from the system can indicate either a leak or condensible gasses making their way out of the oil.

300 microns of mercury for at least an hour would be the minimum that I would accept for something I was buying.

 

[imok2]

I like a triple evacuation best for field work and I want to get down to 500 microns by 3rd evcauation
1st evacuation
break vacuum with dry nitrogen
2nd evacuation
break vacuum with dry nitrogen
3rd evacuation to 500 microns
By introducing dry nitrogen into an evacuated system a couple of times you help to "blot up" residual moisture. Dry nitrogen is capable of absorbing a small quantity of moisture. You might consider the habit of introducing nitrogen just through the high side (especially when in the nitrogen pressure testing process) That way you can see if there is high side to low side flow. If you determine that there is a restriction, it will be easier to rectify the situation now rather than later when you try charging the system.

 

[lcleveland]

the vacuum required is a direct result of the boiling point of the refrigerant being used in the system.if the system is say r-22 with a -40f boiling point the triple down to <500mic is a well established and proven method.But when the system uses say r-23 with a boiling point of -116f the 50 to 25 mic method is a must. the reason is that the vacuum is to pull the non condensables out of the system,r-22 does not produce low enough temp to condense say co2 which condenses below -109f. moisture in a system does not have to be h2o . best advice is good equipment and patience,and remember most hoses and gage sets are for charging,deep vacuums ,below 100mic are best achieved with solid tubing and a micron gage.