A Race To 500 Microns

Gary McCreadie is an HVAC tech, the creator of hvacknowitall.com and the HVAC Know It All Podcast

The science on how we pull an evacuation on air con and refrigeration techniques has modified through the years.  Again within the day, technicians would purge refrigerant via the system to take away air, moisture and different contaminants.  The introduction of POE oil has positively modified the dynamic of this, as POE is hygroscopic, that means it absorbs moisture from the air.  

Because it pertains to this text I want to give attention to a specific job that was accomplished on a compressor trio (3 compressors piped in parallel to make up one circuit) on a McQuay air cooled chiller.  

The Job

The system had a failed compressor, the compressor was changed on the R22 system which contained a combination of mineral oil and POE oil.  The POE oil was launched from a earlier compressor change, as the brand new compressor from earlier and the brand new one within the current have been each shipped with POE.  After the change a strain take a look at was carried out with nitrogen, the take a look at held up over a 24 hour interval.  

At this level an evacuation have to be carried out to take away air, moisture and different system contaminants.  Many technicians use a manifold gauge to drag a vacuum on techniques however this may take longer as a manifold gauge has extra potential leak factors and restrictions, the 1/4″ charging hose permits gives restriction.  

The Set Up

We will eradicate these restrictions from our set ups by using giant diameter hoses, eradicating Schrader cores and eliminating manifold gauges.  Many technicians I communicate to get confused on how this arrange works, “how do I put the cores again in?”, is usually the query.  Utilizing a core removing device will permit techs to take away cores and re- set up them when wanted.  The core removing device is a whole meeting that features a core remover stem, a ball valve and generally an auxiliary tee. The ball valve means that you can isolate the system from the pump, this has many benefits like permitting you to carry out a decay or rise take a look at and eradicating or putting in cores underneath strain. 

Examine Out The Video Of A Schrader Core Elimination Device In Motion

A sure-fire strategy to eradicate a manifold is to run vacuum rated hoses from the system to the pump.  Many vacuum pumps are manufactured with a number of ports constructed into them and often in several sizes as nicely.  Vacuum rated hoses vary in dimension however commonest are 3/8″, 1/2″ and Accutools has developed the TruBlu hose which is 3/4″ in diameter. 

You’ll need to make use of a micron gauge positioned someplace on the system aspect, not on the pump aspect, to watch evacuation efficiency, it’s suggested to maintain the gauge up proper to keep away from any system contaminants from coming into.

Examine Out The Video Of The TruBlu Hose Racing A 1/4′ Hose To 500 Microns

The Steps

After the strain take a look at is full….

Observe: it’s vital to make sure your vacuum pump oil is contemporary and freed from contaminants, a easy oil change can treatment this.  Additionally, it’s suggested to periodically carry out an final vacuum take a look at in your pump previous to evacuation.  That is finished by putting your micron gauge straight onto the pump itself.  Activate the pump and make sure the micron studying reaches the identify plate final vacuum of the pump.  

• Add core removing assemblies to the system and take away the cores.  
• Connect giant diameter hoses to the core removing assemblies and run them to the vacuum pump.  
• Place micron gauge on the system aspect, not the pump aspect, to watch evacuation efficiency. 
• Begin pump and open up core remover ball valves.  
• As soon as closing evacuation is full, 500 microns or beneath, though some business consultants are advising that even decrease is required.  Shut off the ball valves on the core instruments and monitor an increase or decay within the strain on the micron gauge.  A quick sharp rise could point out a leak within the system and a gradual gradual rise that flattens could point out additional evacuation should carried out as contaminants nonetheless exist. 

As soon as the rise take a look at is full we should add the refrigerant cost both from a tank or by opening up system service valves.  As refrigerant is added, to a slight optimistic strain, it’s suggested to take away the micron gauge, re-install Schrader cores and take down the evacuation arrange. Then add the remaining cost to the system.  

Job Website Evacuation 

The steps above are generalized and do not all the time replicate job website situations.  Let’s speak in regards to the compressor job from above.  The identical techniques have been employed as beforehand acknowledged however after a 20 hour evacuation the system was just below 1000 microns.  Take into account that the pump ran over evening with temperatures beneath freezing, an evacuation can wrestle in colder temperatures as moisture can freeze inside a system.  Small ice droplets can type and decelerate the method.  Sublimation, a stable to a gasoline, will happen underneath these situations however can cut back evacuation instances particularly in colder ambient situations.  

I carried out a sweep with nitrogen (purging the system with nitrogen), modified the vacuum pump oil and turned on each receiver and evaporator bundle heaters.  The warmers are utilized in excessive chilly temperatures to maintain system pressures up.  The vacuum pump was restarted and the system was introduced right down to 2000 microns and two extra nitrogen sweeps have been carried out.  The warmers will assist to boost system inner temperatures, the brand new oil will seize extra contaminants and the nitrogen will probably soften fashioned ice droplets because it passes by and permit them to vaporize extra simply throughout evacuation pull down.  The pump ran for an additional 48 hours and on arrival to website, the system had achieved 335 microns.

Examine Out The Video From The Job Above Which Explains In Element The Outlined Steps

Abstract

Some techniques require a bit extra consideration particularly bigger machines which have been round for some time.  Smaller, newer techniques should have no points knocking down so long as the system is tightly sealed.  Implementation of enormous diameter hoses, eradicating restrictions and potential leak factors will guarantee your evacuation is environment friendly as doable.  Triple sweeps with nitrogen could assist in some instances however I do discover it isn’t often wanted. Eradicating your micron gauge at a slight optimistic strain, whereas charging, will guarantee it does not endure any harm.   

Gary McCreadie

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