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.
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.
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.
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.
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.
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.
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.
There are 25,400 microns in an inch. Therefore, with a compound gauge reading 0 inches to 30 inches, there are 762,000 microns.
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.
The blank-off valve acts no different than a water valve. Open it, and with the pump running you will get your desired vacuum. Close it, and with the pump running there is no vacuum.