Why does the micron gauge slowly fall back and then start to hold after pulling a vacuum and blanking-off?

Why does the micron gauge slowly fall back and then start to hold after pulling a vacuum and blanking-off?

The reason for this is there is equalization within the system. If you pull a vacuum lower, it will then fall back at a shorter range and hold.

How low of a vacuum should we pull on a system?

How low of a vacuum should we pull on a system?

JB recommends that a system be pulled to at least 250 microns and held at least five minutes. On any polyester oils in a system, it is recommended to pull a much lower vacuum as moisture is very difficult to remove even with heat and vacuum.

Can I mount my micron gauge onto the vacuum pump?

Can I mount my micron gauge onto the vacuum pump?

It is not recommended to do so as you are reading what the pump is doing and not what the pump is doing to the system (see DV-29). It is suggested that you tee off on the suction side of the system and mount the gauge there.

I am able to pull a vacuum on my system, but when I blank-off, the micron gauge rises rapidly.

I am able to pull a vacuum on my system, but when I blank-off, the micron gauge rises rapidly.

Unless you are using JB`s DV-29, copper tubing, or flexible metal hoses, it is not recommended to use your existing manifold and hoses for blanking-off a system to check for leaks. Hoses work very well under high pressure. Vacuum is very critical in leaks, more so than pressure. All charging hoses, including the black hoses 1/4″ or 3/8″ permeate. Where the crimp is on the brass to the hose also has possible leak issues, and the gasket at the coupler is a major leak offender. The vacuum industry uses O-rings on most couplers. When you screw down on a gasket, it goes into many contortions and will not seal. When using an O-ring, you screw down on it to get a metal to metal seat and the O-ring lies around the lip of the flare giving it a positive seal.

I have been pulling a vacuum on my system using a micron gauge and cannot get it down to a low reading.

I have been pulling a vacuum on my system using a micron gauge and cannot get it down to a low reading.https

See FAQ #1. Another possibility is that some oil may have entered the micron gauge and is giving false readings. The remedy is to pour regular rubbing alcohol into the connector on the micron gauge, shake, and pour out (do not use a q-tip, rag, or any other material – use the liquid alcohol only). Do this about three times, then try to pull a vacuum with the gauge.

I have been using my low side gauge to pull a vacuum, is this wrong?

I have been using my low side gauge to pull a vacuum, is this wrong?

YES. The low side gauge knows only atmospheric pressure and cannot sense moisture or non-condensables. A micron gauge is a heat sensing device that not only reads atmospheric pressure, but also measures the gases created by the vacuum pump as it boils the moisture. For example, if you were to pull a vacuum on an enclosed bottle of water, the low side gauge when pulling a vacuum will read a perfect vacuum. Using a micron gauge, it will immediately tell you with a high reading the you have a problem in you system.

If I use a larger CFM pump, will I be able to pull a vacuum on a system faster?

If I use a larger CFM pump, will I be able to pull a vacuum on a system faster?

In most cases NO. Using a vacuum pump on air conditioning systems from 1 ton to 10 tons, you will not see the difference between a 3 CFM pump and a 10 CFM pump. For example, if you put a pump on a system and you notice within 2 minutes the pump quiets down and you cannot really feel any air leaving the exhaust. This means that there is no more CFM left in the system and you are now working with molecules. Thus, at this point if you replaced a 3 CFM pump with a 10 CFM pump, there is no change in vacuum or time.

What is a gas ballast and how do I use it vacuum pump?

What is a gas ballast and how do I use it?

On the initial pull of vacuum on a system, the gas ballast is open allowing the initial volume of air in the system to bypass the oil so as to not contaminate the oil immediately. When the pump starts to quiet down, close the gas ballast and the pump will start reducing atmospheric pressure in the system to boil the moisture and non-condensables.